Tag Archives: Concrete

A Well-cast Stone (in Concrete)

slaton patterson FAILURES
Deborah Slaton, and David S. Patterson, AIA

Cast stone is a highly refined architectural precast concrete manufactured to resemble natural building stone. Its popularity was related to the rapid development of the portland cement and concrete industries in the late 19th century, with numerous patents taken out for a range of related products.

Employed as a cost-effective alternative to building stone for architectural ornaments or wall claddings, the material is fabricated with various mixes to resemble different natural stone types. Similar to precast, it is subject to failures including surface erosion (i.e. weathering of paste and aggregate), crazing (i.e. fine hairline cracking), cracking, and delamination.

Deterioration may result from corrosion of embedded metals, as well as cyclic freezing and thawing. Issues during fabrication may include improperly graded aggregate (resulting in an overly porous material vulnerable to deterioration) or poor compaction, consolidation, or curing, which can lead to delamination and other distress.

The cast stone cornice on this 1920s building is severely deteriorated due to water infiltration through open joints and cracks, and corrosion of steel reinforcement. The dark gray area is a failed cementitious patch. Photos courtesy Kenneth M. Itle

The cast stone cornice on this 1920s building is severely deteriorated due to water infiltration through open joints and cracks, and corrosion of steel reinforcement. The dark gray area is a failed cementitious patch. Photos courtesy Kenneth M. Itle

Corrosion of embedded, unprotected steel can lead to cracking and delamination. Ferrous staining may indicate presence of corroding metal within or behind the cast stone units. Where steel reinforcement and anchorage components are located too close to the cast stone surface, spalling of the adjacent cast stone can occur. Less common problems include:

  • deterioration of specific components of the cast stone (e.g. aggregate, cement);
  • reaction between components (e.g. alkali-silica reaction);
  • fading or deterioration of pigmented facing layers; and
  • failures due to improper mix proportions or use of inappropriate admixtures.

Repair procedures for cast stone should follow methods and techniques for precast concrete. Corroding embedded metals should be exposed, cleaned, and coated, or removed and replaced. New reinforcement or anchorage should be stainless steel, if possible. Patching materials must be compatible with the original mix—compositional analysis of samples of the existing cast stone and preparation of trial repairs are required to achieve an aesthetic match.

This cast stone coping on a 1990s building exhibits significant cracking attributed to water infiltration, corrosion of embedded steel, and cyclic freezing and thawing.

This cast stone coping on a 1990s building exhibits significant cracking attributed to water infiltration, corrosion of embedded steel, and cyclic freezing and thawing.

A delaminated facing layer can sometimes be repaired by through-face pinning with fine diameter stainless steel anchors. Cleaning procedures for cast stone should use the gentlest approach possible. After repair or cleaning, clear penetrating sealers may be appropriate to reduce moisture infiltration in cast stone.

Severely deteriorated units cannot be repaired. In these cases, research and analysis of the original cast stone can help develop an appropriate mix to match color and texture for the replacement unit. As with concrete, the durability of new cast stone can be enhanced by using air entrainment; quality control during fabrication is essential.

The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect those of the CSI or The Construction Specifier.

Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates, Inc. (WJE) in Northbrook, Illinois, specializing in historic preservation and materials conservation. She can be reached at dslaton@wje.com.
David S. Patterson, AIA, is an architect and senior principal with WJE’s Princeton, New Jersey, office, specializing in investigation and repair of the building envelope. He can be e-mailed at dpatterson@wje.com.

Specifiers cautioned in use of adhesive anchors

by Gary Higbee, CSI, AIA

Contractors in Arizona participate in an American Concrete Institute-Concrete Reinforcing Steel Institute (ACI-CRSI) adhesive anchor installer certification program. Photo courtesy ACI Arizona Chapter

Contractors in Arizona participate in an American Concrete Institute-Concrete Reinforcing Steel Institute (ACI-CRSI) adhesive anchor installer certification program. Photo courtesy ACI Arizona Chapter

Designing proper construction details is an important part of architecture and engineering practice that involves more than just a grasp of building technology. If designers are not also alert to market conditions, then their details—no matter how elegant—can be ineffective and hinder the pace of a project. Overlooking the complications surrounding the specification of adhesive anchors is a prime example, as recent code changes regarding their use threaten to stall building projects in some of the United States’ largest jurisdictions.

The complications stem from the International Building Code (IBC) referencing a provision in American Concrete Institute (ACI) 318-2011, Building Code Requirements for Structural Concrete, requiring workers installing adhesive anchors in certain orientations to have ACI certification. In big construction markets poised to enact the provision, such as New York City, contractors are finding a lack of opportunities for their installers to become certified places them in an impossible position. They cannot use adhesive anchors on jobs unless their installers are certified, and if they install without certification, they risk a violation or stop work order.

How did this problem arise? It seems the only path to certification is by completing ACI/Concrete Reinforcing Steel Institute (CRSI) Adhesive Anchor Installation Certification Program—a two-day course costing from $500 to $900 per person and requiring success in both written and skills tests.

The hurdle is ACI restricts the training and testing to entities it designates. Typically, these are ACI chapters, which, in the larger construction markets are ill-equipped to handle the volume of requests. In New York City, the group tapped to provide this training (one of only three sponsoring groups throughout the state) is only able to certify 15 to 20 installers each month.

With many building trades installing adhesive anchors, this will only produce a small percentage of certified installers needed in the city for projects getting underway in 2015. Solutions such as sending installers to programs out of the city for certification are unlikely to make a dent in the need and only add to the training’s cost. Since ACI developed the certification requirement in response to the anchor failures that caused the collapse of several ceiling panels in the Boston Tunnel of Big Dig infamy, it is surprising this deficiency has not received more attention.

Impact on the industry
The bottleneck resulting from this shortage of training opportunities has the potential to interrupt construction schedules citywide. In correspondence with Louis J. Coletti, president/CEO of the Building Trades Employers Association (BTEA), the author was warned “at least 40,000 tradespersons must be certified by the effective date of the new code if we are to avoid stalling major public and private projects in the city.”

For specifiers, steering clear of adhesive anchors in favor of other types is a way to elude this glitch. However, in some applications, these products may be the preferred, or only acceptable, anchorage method because of the superior holding power in cracked or damaged concrete. Thus, it is important to clarify not all adhesive anchor installations require the installer to be certified. Only when anchors are installed in a horizontal or overhead orientation and under a sustained tension load is the ACI requirement applicable.

Due to the history of failures in these orientations, ACI requires special inspection. This adds to both the project team’s responsibilities and expenses. The architect and engineer must identify on plans filed with a building department those adhesive anchors for which special inspection is required. Subsequently, the owner must engage an independent testing laboratory to perform the inspections, which ACI 318-11 requires to be continuous—meaning no drilling and installing of adhesive anchors should occur unless an inspector is observing the installers’ procedures.

The special inspector must furnish a report to the engineer of record and to the building official affirming whether the installation procedures and materials covered by the report conform to the approved contract documents and the manufacturer’s printed installation instructions. However, before any installation is performed—and this is critical—the inspector must verify the installer’s certification. This circles back to the original problem: limited opportunities for installers to get certified.

While the designers and owners incur added costs and responsibilities, only the contractors are accountable for maintaining certified personnel to perform the installations. If construction activity is to move forward without expensive delays, these contractors must be able to find certified installers.

Until alternatives—such as moratoriums on enforcement, and permitting other qualified entities to conduct the certification training—are in place to address this looming problem, designers should be alert to the potential for added costs and delay when specifying adhesive anchors for installations requiring special inspection.

GaryHigbeeAIAGary Higbee, CSI, AIA, is the director of industry development for the Steel Institute of New York (SINY) and the Ornamental Metal Institute of New York (OMINY). Formerly the assistant director for technical services with New York State’s Building Codes Division and in architectural practice for three decades, he served in various capacities throughout this period on NYS, HUD, and ICC code drafting and development committees. Higbee is a member of the American Institute of Architects (AIA), American Institute of Steel Construction (AISC), American Society of Civil Engineers (ASCE), along with other national associations. He can be reached at higbee@siny.org.

Innovation with Insulating Concrete Forms

Photo courtesy Nudura Insulated Concrete Forms Ltd.

Photo courtesy Nudura Insulated Concrete Forms Ltd.

by Andy Lennox

In the construction industry, ‘innovation’ can be viewed as speed or efficiency of construction, increased durability, sustainable, new materials, systems, or processes. While innovation can also translate into safety and other aspects, it is generally spurred by economic benefit—for example, the speed of construction is a major driver, as its achievement offers cost advantages from labor, financing, and occupancy perspectives. Such is the case with insulating concrete forms (ICFs).

The ICF technology has been in the North American market for almost a half-century. It has recently made great strides over the past 25 years in the residential realm as market forces—such as lumber’s fluctuating price—have put the industry in the position of looking for other material solutions. However, over the last decade, there has been a move to use ICFs in commercial and high-rise residential applications. ASTM E2634, Standard Specification for Flat Wall Insulating Concrete Systems, describes the requirements for the manufacture of units for walls with uniform cross-sections. The respective concrete standard is American Concrete Institute (ACI) 318, Building Code Requirements for Structural Concrete.

ICFs are a permanent formwork system for reinforced concrete construction. The interlocking modular units are dry-stacked into position and filled with concrete. They can be used for almost any concrete wall—interior or exterior, below-grade or above-grade, short or tall. The concept can be seen as the marriage of two proven technologies: concrete mass sandwiched between two layers of expanded polystyrene (EPS) foam insulation.

A traditional exterior concrete wall contains six building components:

● concrete;
● reinforcement bar;
● insulation;
● air barrier;
● vapour barrier; and
● studs/strapping.

ICFs combine these six components into a single building system installed by one crew at the same time. The thermal mass effect of the concrete enhances the insulation’s energy efficiency and the forming system’s airtightness, creating an opportunity for owner/developers to realize savings through the operation of the building.

ICFs can also minimize drywalling and electrical work onsite, but care must be taken with the placing of concrete in any form. Vibration is the key to proper consolidation, specifically around windows and doors. Specially designed door and window bucks are used for ICF systems—some are proprietary and some are site-manufactured.

With innovation, there sometimes are unexpected discoveries with the use of new technology in an application. For example, innovative contractors who used the ICF system in a non-residential application found there were significant constructability advantages with the speed of construction in addition to the high-performance attributes of the ICF wall. In Canada, one Ontario builder saw a significant uptake for the construction of high-rise residential student residences. The speed of construction recognized by the owner/developers provided them with completion dates that not only saved them money, but also achieved the early occupancy they required.

This article highlights growing use of ICFs in four sectors in North America—hotels, mid-rise, schools, and tall walls—to show how the building technology significantly enhanced the speed of construction.

This insulating concrete form (ICF) tall wall bracing mechanically fastens to the concrete core in the wall and provides 2.1-m (7-ft) work and wind bays every 10.7 m (35 ft). Photo courtesy Logix Insulated Concrete Ltd.

This insulating concrete form (ICF) tall wall bracing mechanically fastens to the concrete core in the wall and provides 2.1-m (7-ft) work and wind bays every 10.7 m (35 ft). Photo courtesy Logix Insulated Concrete Ltd.

Building hotels with ICFs can allow construction to advance at a rate of one fl oor per week. Photo courtesy Nudura

Building hotels with ICFs can allow construction to advance at a rate of one floor per week. Photo courtesy Nudura

 

 

 

 

 

 

 

 

Hotels on the horizon
Hotel builders are seeing the benefits ICF construction can offer in various areas. The faster a hotel can open, the sooner its owners start generating revenue. With insulating concrete formwork, construction typically progresses much faster than traditional concrete masonry unit (CMU) block construction—this factors in ICFs being insulation, forming, and attachment surfaces all in one, whereas the block is but one component. In other words, ICFs combine formwork, structure, interior and exterior strapping, and air and vapor barriers, resulting in more efficient construction with less sub-trade congestion onsite. On average, installers are able to complete a floor a week, depending on the project size. The various manufacturers provide specialized training for the application of their proprietary system.

Another contributing factor to getting the hotels open sooner is the ability to build in differing climates. Weather can play a key role in any construction project; winter can often halt a job entirely. The versatility with ICFs offers builders the advantage of building year-round. This is because the curing process offered by the forms means concrete can be poured on the coldest days. The EPS foam containing the concrete actually serves to store the natural heat produced inside the concrete core during the hydration or curing process. Studies have proven concrete installed in this condition can be placed and maintained at temperatures as low as −20 C (−10 F), even sustained for as long as three days.1 In such conditions, the process of hydration has been proven to increase to levels as high as 27 C (80 F) within the formwork, based on a concrete core of 160 mm [6 ¼ in.] thick.

National model energy codes, such as the International Energy Conservation Code (IECC), are advancing the way in which commercial and residential exterior wall construction is approached by emphasizing the use of continuous insulation (ci) systems. As the name suggests, these assemblies provide a continuous insulation layer over an entire wall, rather than just in the wall cavities. With other traditional building systems on the market, this ci layer has to be applied, but it is an integral part of ICFs.

In addition to energy performance benefits, ICFs are non-combustible and can offer fire protection ratings of up to four hours. As an added advantage for hotels, the assemblies also provide greater sound attenuation, offering sound transmission class (STC) ratings of up to 55—the material provides a further break than traditional concrete, thanks to the addition of the insulation changing the material density. EPS, the key component of ICF products, is also resistant to mold growth, lowering long-term maintenance costs for owners compared to wood-frame hotel construction.

For this ICF-intensive condominium project, the normal percentage of insulating concrete forms was doubled by incorporating the assemblies for not only walls, but also suspended fl oors and roofs. Photos courtesy Quad-Lock Insulated Concrete Forms Ltd.

For this ICF-intensive condominium project, the normal percentage of insulating concrete forms was doubled by incorporating the assemblies for not only  walls, but also suspended floors and roofs. Photos courtesy Quad-Lock Insulated Concrete Forms Ltd.

Complex reinforcing requirements presented installation challenges overcome by an ICF design offering separate panels and ties that fi t around the rebar.

Complex reinforcing requirements presented installation challenges overcome by an ICF design offering separate panels and ties that fit around the rebar.

 

 

 

 

 

 

 

 

 

 

 

Mid-rise revolution
One great success story in mid-rise ICF construction is the La Concha Pearl condominium project in La Paz, Mexico. ICF installation on this seven-story, 33-unit luxury beachfront development took place over an eight-month period, putting the building into service far ahead of the expected norm in the region. The sales team reported the reduction in the ‘pre-construction’ sales phase, where potential customers had no real building to see, was a huge benefit in persuading would-be residents to buy. If this holds true for other projects, there may be more developers and owners actively requesting ICFs.

In this particular case, the developers, having already made a commitment to minimize the impact on the local community, undertook some re-design of the building to optimize it for ICF, minimizing wasted materials and time onsite. The design phase was also shortened because the ‘flat-wall’ ICF design meant the project engineer could confidently rely on known, published design parameters for poured-in-place concrete structures via American Concrete Institute (ACI) 318, Building Code Requirements for Structural Concrete. Though a departure from the more common masonry block building found in the region, the project engineer and local building officials were well within their comfort zone, meeting no unfamiliar challenges posed by ICFs.

The general contractor, despite starting with only a few experienced ICF hands, was able to offer great training and oversight. His efforts resulted in a doubling of average production over the course of the 240-day installation, cutting the average time-per-floor in half. Crews quickly and eagerly accepted the new technology, taking great pride in learning a new craft.

The La Concha Pearl project is ICF-intensive—the assemblies were employed for both walls and floors, more than doubling the usual amount of concrete forms found on the typical project. Only 43 per cent of the total ICF area was a wall system; the majority was used for the floors.

The general contractor reported that, once shoring was in place, his crew would lay an entire 557-m2 (6000-sf) floor in about three hours, using the ICF T-beam floor forms. Since ICF floor forms replace about half of conventional suspended floor forms, post-pour removal of only primary shoring frames and beams was easily and quickly completed. Resumption of construction on the succeeding upper floors was never delayed, as each floor was fitted with a minimal amount of re-shoring (temporary posts) to carry construction loads through to the ground-floor level.

As an additional note, the La Concha project is situated in an extreme seismic zone. This led the project engineer to an extreme reinforcing bar specification. On lower floors, a double mat of steel, pre-tied into place, was specified. The knock-down design of the ICF wall system allowed the crews to fit ICF components through the pre-tied rebar mats, row by row, without disturbing pre-positioned reinforcing.

Crews often quickly adapt to ICF technology, increasing their production rates as the project progresses.

Crews often quickly adapt to ICF technology, increasing their production rates as the project progresses.

The speed of construction offered with ICFs can mean early completion dates for owners and fi nancial benefi ts. Photos courtesy Logix Insulated Concrete Forms Ltd.

The speed of construction offered with ICFs can mean
early completion dates for owners and financial benefits.
Photos courtesy Logix Insulated Concrete Forms Ltd.

 

 

 

 

 

 

 

 

School sounds
In Pincher Creek, Alberta, a 930-m2 (10,000-sf) private school was built utilizing ICFs. The school board and designers decided on this route for a faster build as well as improved energy, long-term resiliency, and sound efficiency. The contractor was pleased, noted the recorded time spent building with ICF was about half the time of that of a typical wood build, while providing the best in insulation and sound barrier—this latter criterion was especially important given the often-powerful, noisy southern Alberta winds.

The ICF walls included the standard 1.2-m (4-ft) frost wall and 2.7-m (9-ft) walls, with 3.7-m (12-ft) walls for the gymnasium. No other form of insulation or vapour barrier was required by using the forms. The gymnasium walls provided an especially strong barrier for sporting activities with no need for plywood, which would have otherwise been required behind the gypsum in wood builds. The solidness and strength of rebar-reinforced ICF blocks was a definite factor in the choice to employ this construction methodology.

During construction and concrete pouring, use of ICF bracing made it easy to straighten walls while providing solid, safe scaffolding for construction workers. The design of the block makes it a quick and efficient to attach the upright channels for bracing utilizing simple screws. Workers have a safe platform to work from, with a built-in hand rail and no need for tie-offs that would normally be used with other construction scaffolds.

The school board was satisfied with the decision to choose ICFs in the construction of the school. In the few years since completion, there have been no complaints or issues. The fewer labor-hours in the building of the school continues to be a deciding factor for the contractor and architect as they have since used ICFs in other construction business and plans design.

Whether for retail or hospitality applications, completed ICF projects should yield sustainable, resilient, comfortable, and effi cient buildings.

Whether for retail or hospitality applications, completed ICF projects should yield sustainable, resilient, comfortable, and efficient buildings.

Photo courtesy Nudura Insulated Concrete Forms Ltd.

Photo courtesy Nudura Insulated Concrete Forms Ltd.

 

 

 

 

 

 

 

 

Greener education
Richardsville Elementary (Warren County, Kentucky) is the first net-zero ICF school in the United States. Designed by Sherman-Carter-Barnhart Architects and engineered by CMTA, this building was constructed to be a two-story, energy-efficient structure that incorporates renewable materials and insulated concrete forms for its superior building envelope.

Generating its own energy, the 6715-m2 (72,285-sf) Richardsville is the next generation of educational building standards, and a valuable tool to educate students on energy and water conservation as well as the value of recycling. The project is designed to use only 18 kBtu/sf annually—75 percent less than the nation average standard set out by American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings.

Richardville was a learned lesson from previous schools built with ICFs elsewhere in the Bluegrass State. During construction onsite, the Warren County School District experienced reduced time in construction schedules. With CMU-constructed schools, running electrical can add to the construction schedule. Tyically, conduit has to be placed and fished through the walls. ICF construction offered this project’s electrical contractors the ability for quick installation times and having the wiring easily accessible on the face of the wall.

Tall walls
Retail chain Cabela’s is one the world’s foremost outfitters of hunting, fishing, and outdoor gear. Looking for energy efficiency and lower long-term operating costs, its architectural firm specified insulating concrete forms for the exterior walls of a new facility in Saskatoon, Saskatchewan. As the project progressed, it became evident ICFs not only delivered high-performance tall walls, but also a faster build.

This Cabela’s store measures about 64 x 64 m (210 x 210 ft) with the exterior tall walls ranging from 8.8 to 9.5 m (29 to 31 ft) in height. The wall’s assembly included six construction steps:

● concrete core;
● steel reinforcement;
● exterior and interior insulation;
● air barrier;
● vapor barrier; and
● stud work/furring strips.

According to 2014 RS Means data, if these walls were built with CMUs and finished to the same degree, the expected labor rate to build a comparable wall assembly would be 0.217 man-hours per square foot. On this particular job, however, the ICF installation crew recorded a labor rate of 0.109 labor hours per square foot. This suggests the walls were completed using half the labor that would have been traditionally required.

Several factors contributed to this speed. For example, the exterior tall walls were designed for maximum efficiency. The 203-mm (8-in.) concrete core provided sufficient room for rebar placement and concrete consolidation. The horizontal rebar was specified at 406 mm (16 in.) on center (oc) to be consistent with the course height of the ICF system.

By specifying the vertical rebar at 20m at 406 mm oc (versus, say, 10m at 203 mm oc), less bar had to be handled and placed, resulting in lower labor costs and easier and quicker concrete consolidation. Further, the designers were mindful of the ICF block dimensions in order to minimize the time spent cutting the blocks to make them fit.

Unassembled (i.e. knockdown) ICF blocks were assembled around the pre-built rebar cages used in the pilasters every 6 m (20 ft) of tall wall. This was much faster than the alternative method of building the rebar cages around the in-situ ICFs. Rugged rebar chairs built into the webs enabled the 6-m lengths of horizontal rebar to be quickly ‘snapped into place’ by a single crew member. Additionally, slide-in end caps quickly terminated wall sections and created vertical seams for expansion control.

Contact lap splices were used in the corners to allow concrete to easily flow through the corner forms. Use of running bonding (as opposed to stack bonding) was also maximized to reduce the installation and removal of temporary form support on both sides of the tall walls. Protecting the interlock during the concrete pours also eliminated any potential delays during subsequent course placement.

Further, the tall-wall scaffolding bracing system (which can be used to brace ICF walls up to 38 m [125 ft] without additional engineering) had many additional time-saving features. For example, it quickly connected directly to the concrete core providing an improved safety factor (required by Occupational Safety and Health Administration [OSHA] standards) and the ability to quickly precision-plum the walls.

As the guardrail was attached, no tie-offs for the crew members were required. The scaffolding’s wind-bays, which also function as 2.1-m (7-ft) work-bays, were located every 10.1 m (35 ft)—this means material was easily available at high heights. With extra scaffolding onsite, sections could be erected while others were being taken down.

Conclusion
Insulating concrete form applications are only limited by the designers. Some applications may require small redesigns to handle the structural loads, but many of these formwork systems have specially designed blocks or sections to deal with any unusual details. Technological advances are also allowing the creation of larger units, which will speed up construction even more.

The recent formation of the Council of ICF Industries (CICFI) is also expected to yield additional resources for building owners and project team members interested in exploring the suitability of this material. The group represents itself as the voice of the North American ICF manufacturing industry, and will serve as the information source for all information about the forms.

Notes
1 For more, see the report, “Cold Weather Construction of ICF Walls” by John Gadja (Portland Cement Association [PCA], 2002). (back to top)

Andy Lennox is a vice president of Logix Insulated Concrete Forms Ltd. He has worked in the ICF industry for 17 years in various sales, marketing, and management capacities. Lennox is the inaugural chair of the Council of ICF Industries (CICFI). He can be contacted by e-mail at andy@logixicf.com.

Association Cooperation

In the October issue of The Construction Specifier, authors Ward R. Malisch, PhD, PE, and Bruce A. Suprenant, PhD, PE (both of the American Society of Concrete Contractors [ASCC]) wrote our cover story, “Bridging the Specification Gap between Divisions 03 and 09: Concrete and Floorcovering Associations Unite.” The piece looked at how their association teamed up with six other flooring groups to find a solution to a ‘specification gap’ between Divisions 03 and 09 in terms of floor surface flatness requirements.

For space reasons, we had to hold off including a little more background on how these associations collaborated. That ‘missing’ information follows, in the words of Malisch and Suprenant:

The impetus for developing the American Society of Concrete Contractors (ASCC) Position Statements came from a group of contractor members who became aware of a paper published by a national wood flooring organization—not, it should be noted, the National Wood Flooring Association (NWFA)—that stated the organization did not believe in F-numbers and felt they should not be used to measure slabs for gym floors. Rather than trying to decide how they could build a floor that meets unreasonable requirements, ASCC contractors realized they needed to spend their time and resources to educate the industry on the limitations of concrete floors. Thus was born this series, including ASCC Position Statement 6, Division 3 versus Division 9 Floor Flatness Tolerances.

Then, rather than continuing to fight their fellow contractors in the floorcovering industry, ASCC made an effort to get them on board, realizing the greater strength of a united front. ASCC first approached NWFA. With only minor rewriting, that association was eager to endorse the Position Statement.

“For the first time, instead of disagreeing, the two sides have come together to find a common solution to a problem that has cost both groups hundreds of thousands of dollars in rework,” said NWFA president/CEO Michael Martin.

Shortly thereafter, ASCC invited the National Tile Contractors Association (NTCA) to participate in a panel discussion on this topic featuring contractors and technical personnel from both disciplines. Both sides acknowledged the wisdom of a bid allowance to compensate for the incompatibility of the measuring methods, and NTCA became the second flooring association to sign on.

Bart Bettiga, NTCA executive director, commented on the reasons for the document’s usefulness.

“It is our belief this position statement is one of the most important documents we have supported in the past several years,” he said. “This statement accomplishes its goals on many levels. It educates the construction professional about important considerations that must be taken when specifying floorcovering products over concrete substrates.”

“The most important point emphasized in this position statement centers on the disparity related to meeting industry standards in the respective divisions,” Bettiga continued. “Equally important is the call for communication between the related parties and for a proactive approach to be determined prior to the commencement of the work. We strongly support the use of this statement to our members in their communication to the general contractor and architect/specifier on their projects.”

These two organizations were followed by the Flooring Contractors Association. Then, last year, Scott Conwell, director of industry development and technical services for the International Masonry Institute (IMI) contacted the ASCC, asking to add the group’s name, along with those of the Tile Contractors Association of America (TCAA) and the International Union Of Bricklayers and Allied Craftsmen (BAC) to the list of supporters.

“This ASCC Position Statement succinctly brings to light the disparity in requirements for floor flatness between the concrete and the ceramic tile trades,” says Conwell. “The paper effectively brings expectations in line, leading to increased cooperation on the job site to make any corrections to the floor that may be necessary prior to installation of the tile finish.”

Two trades with distinctively different practices and obstacles to overcome but with one goal: to deliver a high-quality product to a satisfied owner.

Don’t Seal Your Fate: Considerations for parking garage surface treatments

All photos © Hoffmann Architects Inc.

All photos © Hoffmann Architects Inc.

by Lawrence E. Keenan, PE, AIA and Robert A. Marsoli Jr., EIT

Elastomeric traffic-bearing membranes have soared in popularity over the past decade. But, what should designers know before specifying one at a parking facility?

It is true parking decks must be protected from the harmful effects of moisture and chlorides, but there is a growing misconception installing a traffic-bearing membrane is a one-way ticket to the garage equivalent of immortality. While a traffic-bearing membrane may be the best option for many situations, it is a big-ticket item, and thorough consideration is necessary to determine whether this costly investment is suited to the garage’s needs.

In order to withstand the punishing abrasion which a parking deck must endure, the traffic-bearing membrane must be hard and durable. At the same time, the membrane must be soft and flexible to bridge over moving cracks and joints without failure. However, traffic-bearing membranes are not perfect. Since hard membranes are generally inflexible, and more pliable membranes do not hold up well to abrasion, choosing the right membrane is a balancing act. Additionally, there are locations where no membrane performs well, such as those areas requiring a flexible membrane, yet are subject to snow plows.

Identifying product properties and applying appropriate selection criteria can guide the specifier in developing a customized system that will provide immediate protection, while also considering future treatment options.

For this parking lot, cracks are routed and sealed as part of a concrete repair project.

For this parking lot, cracks are routed and sealed as part of a concrete repair project.

This test core shows epoxy penetration to the bottom of a crack, as indicated by the arrows on the concrete.

This test core shows epoxy penetration to the
bottom of a crack, as indicated by the arrows
on the concrete.

 

 

 

 

 

 

 

 

Sources of deterioration
Since the interior and exterior of parking structures are exposed to the elements, they are more susceptible than other types of buildings to deterioration due to moisture, temperature cycles, and contaminants. Even the best designed and constructed garages need help to survive this onslaught of corrosive forces.

Water is at the heart of most parking deck deterioration. Moisture can facilitate reactions between certain aggregates and alkali hydroxides in the concrete, creating a cycle of expansion, cracking, and further moisture intrusion. Alkali-silica reaction (ASR) is difficult to stop once it has developed. Other minerals, notably sulfates, migrate via penetrating moisture and can lead to formation of gypsum, which can lead to softening and loss of concrete strength, and ettringite, a crystalline mineral the formation of which can result in an increase in solid volume, creating expansive forces that cause cracking and a loss of cohesion and strength in the concrete.

In northern climates, parking decks are subjected to extreme corrosive and deteriorating environments. Moisture, laden with chlorides from de-icing chemicals, tracks into garages and ultimately soaks into the concrete surface. The dissolved chlorides then migrate to embedded steel reinforcement through the pores in the concrete or penetrate through cracks. Once they reach the steel, the salts cause expansive corrosion, ultimately resulting in unsightly, destructive, and costly deterioration.

Moisture’s ability to transport corrosive chlorides is not its only damaging property. Coupled with cold weather, water can damage concrete decks as it expands and contracts during freeze-thaw cycles. Air entrainment, the deliberate incorporation of microscopic air voids in concrete, releases the internal pressure created by freezing water by permitting moisture to flow from void to void. Although this solution to freeze-thaw degradation has been known for years, garages may inadvertently be constructed with insufficient air entrainment, leading to premature concrete breakdown as freezing water destroys it from the inside out.

Applying an epoxy healer/sealer to a concrete deck can be a quick, effective, lowmaintenance option.

Applying an epoxy healer/sealer to a concrete deck can be a quick, effective, low-maintenance option.

Gravity-feeding an epoxy healer/sealer can repair cracks on a concrete deck.

Gravity-feeding an epoxy healer/sealer can repair cracks on a concrete deck.

 

 

 

 

 

 

 

 

 

 

Deck protection: product types
Technological advances in the chemical industry over the past 30 years have brought concrete sealers a long way from the boiled linseed oil previously used. Today, an industry dedicated solely to concrete protection offers a dizzying array of products to treat concrete before, during, and after production.

Ultimately, the goal of parking garage protection is to stop water from getting into the deck. This may be an over-simplification, but no water means significantly reduced deterioration. The tricky part is water comes in multiple forms. Liquid water is an obvious ‘villain,’ as is the expansive force of ice and snow, but water vapor can be just as damaging.

For example, a chloride-laden deck can actually draw moisture from the air and continue to deteriorate even after the best efforts to keep it dry. In fact, calcium chloride, the most popular and effective of all de-icing chemicals, is commonly used on construction sites for dust control. It is sprinkled onto the dry earth and wets the surface by pulling moisture from the air. Unfortunately, it works equally well at saturating a parking deck.

Remediating the effects of chloride ion attack, freeze-thaw damage, or moisture-driven chemical reactions is both difficult and costly, so preventing any type of water infiltration is a priority. While keeping a garage perfectly dry is an impossible task, through thoughtful product selection, the degree to which moisture can penetrate the parking deck can be limited. For existing parking structures, numerous waterproofing agents that can be applied to the deck’s surface are available.

Penetrating sealers
These liquid-applied treatments, which include silane, siloxane, and silicates, stop water entry by penetrating deep into concrete and forming a barrier that prevents water from entering, limiting chloride ion migration and freeze-thaw damage. These treatments are also vapor-permeable, allowing them to be used at locations where other coatings may be inappropriate, such as slabs-on-grade. Since they are inexpensive and quickly applied, with little or no down-time, penetrating sealers offer a good first line of defense for a parking structure that is in good overall repair. As invisible penetrants working below the surface, these sealers do not affect deck line striping, saving on project duration and cost.

However, these coatings can be short-lived solutions, requiring reapplication every five years or less. They also do not bridge cracks, so they only limit moisture and chloride penetration in intact concrete. Since cracking can be an ongoing process, the ability to bridge new cracks as they form may be important in parking decks that already have evidence of concrete distress.

Methacrylate and epoxy healer/sealers
These coatings both repair cracks and seal pores, so they can be used to restore a deck that has already undergone some deterioration. Low-viscosity methacrylates and epoxies fill the pores in concrete to create a barrier to liquid-water-driven chloride intrusion. They can also be injected or gravity-fed into cracks to structurally heal them. Where desirable, healer/sealers can also limit vapor transmission, although care must be taken not to lock moisture within the deck.

Moderately priced, this class of surface treatments offers a good solution for parking structures starting to show some signs of distress, both to treat deterioration that has already occurred and to prevent continued water-related damage.

Where methacrylate and epoxy healer/sealers fall short is in wet or soiled fractures (to which the materials will not adhere) and moving cracks (which are likely to re-fracture). On parking decks exposed to continuous sunlight, epoxies can degrade quickly under ultraviolet (UV) radiation, so methacrylates should be considered for these areas.

For enclosed parking structures or other areas where fumes might be a problem, offensive odors from methacrylates might prove prohibitive. Unlike the penetrating sealers, healer/sealers are not just ‘coat-and-go;’ surface preparation necessitates shot-blasting, which means increased down time and cost. Also, pavement markings must be reapplied.

Traffic-bearing membranes (elastomeric)
In parking structures with dynamic cracking, shrinkage, or more advanced damage, a traffic-bearing membrane may be the only option to address the ongoing deterioration. Unlike the sealers, these do not penetrate the concrete, but remain on the surface to create a barrier that locks out moisture and chlorides. Most elastomeric membranes have two layers—a base coat that provides the waterproofing protection, and a top coat, which protects the base membrane and provides skid resistance. Together, these yield an attractive, easy-to-clean surface that can give a ‘face lift’ to older, crack-riddled parking decks.

However, a traffic-bearing membrane’s assets are also its downsides. Flexible varieties offer superior crack-bridging, even for moving cracks, but they do not hold up well to abrasion because they are soft and yielding. More rigid varieties, designed to better withstand abrasive forces of heavy traffic, are too stiff to bridge these moving cracks. So while traffic-bearing membranes, as a class of surface treatments may seem to have the ideal combination of properties, in practice no single membrane actually does. Before specifying one of these coatings, the lengthy down-time required for preparation and application, and considerable ongoing maintenance of re-coating or top-coating every five to 10 years, should be considered. Once a traffic-bearing membrane has been installed, it is nearly impossible to return to an uncoated surface in the future.

Applying an impermeable coating to the bottom of an elevated deck traps moisture in the slab, leading to accelerated deterioration.

Applying an impermeable coating to the bottom of an elevated deck traps moisture in the slab, leading to accelerated deterioration.

Unable to evaporate through the coated surface, water entering the slab migrates to the reinforcing steel, leading to corrosion and spalls.

Unable to evaporate through the coated surface, water entering the slab migrates to the reinforcing steel, leading to corrosion and spalls.

Cast-in-place vs. precast
To select the best of the available surface treatments for the parking structure’s characteristics, condition, and situation, designers should consider numerous criteria to determine which products offer the best-performing option for the cost, in terms of both initial investment and long-term maintenance.

Over the years, many different types of parking decks have been developed. For the purpose of investigating surface treatment options, deck types can be simplified into two basic categories: cast-in-place and precast concrete. Usually composed of a single, contiguous, reinforced slab of concrete spanning a concrete or steel frame, cast-in-place decks are constructed onsite.

Due to its nature, concrete shrinks as it cures, which coupled with the external restraint stress from the structure to which it is attached, can lead to crack formation. Cracks are water-borne chlorides’ direct route to reinforcing steel. Once established, these cracks form natural expansion joints that open and close with changing temperature and humidity.

Consequently, protective techniques tend to focus on these moving cracks. If cracks are few and the deck is chloride-free, then routing and sealing, and applying a low-cost sealer, may be appropriate. If the deck is riddled with cracks that cannot be adequately sealed, then elastomeric membranes can begin to look like a good option.

Cast off-site under controlled conditions, precast decks are lifted and welded into place after they have cured and partially dried out. Since the concrete used for this type of construction is typically high-strength and denser than its cast-in-place counterpart, precast decks should rarely experience cracking. However, this manner of construction is favored for fast-track projects, and the end result is rarely defect-free.

As these materials are factory-made and must be lifted into place, precast units do not create a single, contiguous, monolithic structure. Instead, the individual members meet at sealant joints. Extending around each precast unit, these joints add up to miles of sealant that must be maintained and periodically replaced. Even if cracking is not an issue, water migration through failed joints can be just as damaging.

Aside from routine sealant maintenance, surface protection requirements are typically minimal and can usually be addressed with simple low-cost penetrating sealers. Heavily cracked decks may be routed and sealed or treated with rigid epoxies or healer/sealers, since these cracks are typically non-moving. However, the precast deck’s irregular surface does not readily lend itself to flexible membrane-type coatings. The leading edge of each panel quickly becomes a wear point, bumping against automobile tires or catching the tip of a snow plow. Protection techniques that soak into the deck and keep the concrete as the wearing surface are preferred.

Painting the underside of a parking deck may not improve its appearance if moisture causes the coating to bubble and peel.

Painting the underside of a parking deck may not improve its appearance if moisture causes the coating to bubble and peel.

In this case, coating patches were used to repair damage from snowplow blades.

In this case, coating patches were used to
repair damage from snowplow blades.

 

 

 

 

 

 

 

 

 

Concrete quality and condition
Knowing the concrete quality offers insight into the type of deterioration to which it would be most susceptible. This is usually achieved by ordering a petrographic analysis of a test sample. A petrographic analysis is an extraordinarily useful tool in determining what is wrong with concrete or predicting what can go wrong in the future. This analysis can detect most durability issues, so the most appropriate level of protection can be selected.

Chloride content is determined by removing concrete samples from varying depths and analyzing them in a laboratory. If chlorides are moving through the concrete quickly, the deck protection system must be aggressively enhanced to stop further migration. If the chlorides have reached the level of the reinforcement, chances are deterioration has already begun and low-cost sealers are no longer an option. Deck protection that retards water vapor intrusion or effectively inhibits corrosion is now necessary.

Age
While there is nothing inherently wrong with old concrete, the life of a deck does tend to follow a natural progression. Unless design or installation defects are an issue, a new deck can be effectively treated with low-cost sealers that limit the intrusion of chlorides through the concrete. Further along in the life of the deck, a more positive barrier, such as a moderately-priced epoxy sealer, may be necessary to retard moisture entry.

Ultimately, if not properly protected, a deck may require a traffic-bearing membrane to provide the best defense. However, as these membranes are costly and require maintenance and periodic reapplication, waiting to address signs of trouble until there are no other options is not the best course of action. Once a deck has begun to deteriorate, the coating can only retard further deterioration, not stop it.

Evaluating the condition of the concrete slab is an important part of the coating selection process.

Evaluating the condition of the concrete slab is an important part of the coating selection process.

Application of a traffi c-bearing membrane can take several days, and re-coating/top-coating may be required every fi ve to 10 years.

Application of a traffic-bearing membrane can take several days, and re-coating/top-coating may be required every five to 10 years.

 

 

 

 

 

 

 

Exposure
Whatever protection system is employed, it must withstand the rigors of its environment. UV degradation may be a problem for some coatings on a top deck. Epoxies, in particular, have difficulties when exposed to direct sunlight. Soft, flexible membranes may not withstand abrasion in high-traffic garages or on a typical turning radius and will fare poorly against snowplows. For example, a coating that looks ‘like new’ after many years in an apartment garage may not withstand a year at an airport or shopping mall.

The damage that can be inflicted by snow removal should not be underestimated. Many coating warranties require snow removal equipment to have rubber tips; others do not cover snowplow damage outright. Unless the garage management operates its own snow removal equipment, coatings at exposed decks will likely encounter a steel plow blade at some point in their service life. There are coating systems tough enough to repel the steel tips, but these super-rigid coatings do not bridge cracks. The best solution depends on finding the right compromise between rigidity and flexibility for a specific situation.

Location
As the adage goes, location is everything. Knowing which surfaces in a parking structure can accept an impermeable coating and which are best left bare is critical to prolonging the life of a garage.

A coating successfully applied to an elevated deck may have disastrous effects in the same garage when applied to a slab-on-grade. As water levels and humidity change, ground moisture seeps up into the concrete slab. Vapor barriers, often installed under slabs-on-grade, are designed to block this moisture from entering the slab. However, in reality, breaches in the barrier or cracks in the slab can still permit water entry. If an impermeable coating is applied to the top surface of the deck, that moisture becomes trapped between two impenetrable surfaces. Unable to escape, the water sits in the slab, leading to chloride and freeze-thaw degradation. Even without a vapor barrier, moisture in the ground rises within the slab and becomes trapped within the deck. Therefore, leaving the slab-on-grade uncoated is the best course of action.

On an elevated deck, that permeability gradient is reversed. Moisture enters the deck from above and migrates through the slab to the underside, where it evaporates. Even with a waterproofing membrane protecting the top surface, the deck is still susceptible to water entering at cracks, joints, and failed coating sections. Coating the bottom of the deck with an impermeable coating invariably leads to trapped moisture and accelerated deterioration. For this reason, the underside of an elevated deck should be similarly treated to a slab-on-grade and left uncoated.

Inappropriately specifi ed or applied coatings can lead to moisturerelated damage that is as detrimental as it is aesthetically unsightly.

Inappropriately specified or applied coatings can lead to moisture-related damage that is as detrimental as it is
aesthetically unsightly.

Cost
While the saying ‘you get what you pay for,’ can be applied to surface protection as well as anything else, in terms of quality material selection and skilled application, it is also true lower-cost systems are usually lower-maintenance alternatives. If an inexpensive sealer would suffice, installing a traffic-bearing membrane because it is the high-end option may mean investing in a costly system that may not perform any better in that situation. Additionally, once the membrane is in place, it must be maintained and eventually replaced.

Aesthetics
While a simple sealer can help prevent water infiltration, it will not change the parking deck’s appearance. On the other hand, an elastomeric membrane transforms the look of the garage and provides a uniform, fresh-looking surface that is easily cleaned of dirt and stains. For a crack-riddled older garage, this can be

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a welcome change. In a newer garage, however, the existing concrete surface is likely fine.

Using paint on the underside of a deck to improve its appearance can have problematic effects, since paint is a type of coating. Many of the concrete paints on the market are epoxy-based and relatively impervious to moisture. Even if a vapor-permeable paint is used, successive reapplications increase the coating thickness and so decrease its permeability. Over time, what was once a high-permeability surface can become surprisingly resistant to moisture migration. With the eventuality of peeling paint, spalls, rust, and cracks taken into account, a deck underside painted only for aesthetics begins to lose its appeal, as compared with a simple, uncoated one still intact.

Coating compatibility
Not all surface treatments are compatible. The parking deck protection specified now may limit future options, so both immediate performance goals as well as long-range planning should be considered before committing to a coating. Any applications already in place should also be investigated.

A ‘quick fix’ to get through the winter, for example, might be a less-restrictive sealer that penetrates the slab—rather than one that coats the surface—because various surface treatments can be applied over it in the future. Epoxy healer/sealers can cover such penetrants, and they provide a good base for membrane systems, should one be installed, down the road. However, once a traffic-bearing membrane is installed there is no way to effectively remove it without damaging the slab surface.

Proper application
Even if the right surface treatment is selected for a given project, problems can still result when the application is not executed correctly. Certain coating deterioration issues—such as delamination and blistering—may be avoidable if care is taken in surface preparation and coating techniques.

Before any coating is applied, surface defects must be corrected in order to create a sound substrate for coating application. Any dirt, dust, grease, paint, or other foreign matter should be cleaned, and surrounding areas protected. To prepare concrete for a penetrating sealer, procedures such as power-washing are often used, wherein high-pressure water or steam, sometimes mixed with mild detergents, forces dirt off an exterior surface. Other methods include hand-scrubbing and simple vacuum or broom cleaning. To prepare the deck surface for healer/sealers or traffic-bearing membranes, shot-blasting is required.

It is crucial to wait a minimum of 24 hours following any kind of water washing before applying a coating, in order to allow the deck to dry sufficiently. Cleaned surfaces should be tested for moisture at various sites just prior to application. If excess moisture remains, the coating may trap it inside the parking deck, exacerbating any water-related deterioration. A damp surface can also cause adhesion problems.

In weather conditions such as extreme heat or cold, wind, or rain, the area must be protected and coatings should not be applied. One must also avoid coating in direct heat of sun, as this may result in rapid drying of the material and cause bubbles or wrinkling. It is important to check the specific temperature range recommended by the manufacturer, as these vary from product to product. Also, keep in mind checking the ambient temperature may not be sufficient as surface temperatures may be significantly hotter or colder.

Conclusion
The preferred protection techniques stop deterioration before it begins. If a parking deck is well-maintained from the start, with sealers applied early and cracks promptly addressed, then surface treatment choices can evolve over time as the garage ages and needs change. However, if conditions are such that distress is advanced and progressing rapidly, more immediate and aggressive action must be taken to slow deterioration and minimize its impact.

Before specifying a concrete coating, one should consider the parking deck type, concrete age and quality, and level of exposure to traffic and weather. A surface treatment must not be specified until the garage’s condition has been assessed through investigation, testing, and evaluation. This can help navigate the array of available coatings. The right parking structure protection program should not only protect the deck today, but also anticipate the maintenance needs of tomorrow.

Lawrence E. Keenan, PE, AIA, is the director of engineering with Hoffmann Architects Inc., an architecture and engineering firm specializing in the rehabilitation of building exteriors. He has extensive experience in parking structure rehabilitation, including investigation, repair, and surface treatment consultation. Keenan can be contacted by e-mail at l.keenan@hoffarch.com.

Robert A. Marsoli Jr., EIT, is a project manager at Hoffmann Architects and has developed remediation solutions for a number of parking garages, from design through administration. He also provides preventive treatment consultation services for new construction. Marsoli may be reached at r.marsoli@hoffarch.com.