Tag Archives: Durability

Durable Waterproofing for Concrete Masonry Walls: Field Testing Methods of Water Repellency

by Robert M. Chamra, EIT and Beth Anne Feero, EIT

There are two main field testing methods used for water repellency of concrete masonry units (CMUs), for quality assurance before being placed in a wall: droplet and RILEM tube testing. Completed assemblies can also be tested with RILEM tubes or other standard water spray tests such as ASTM E514, Standard Test Method for Water Penetration and Leakage Through Masonry.

Droplet testing
The droplet test is a quick and simple test to observe the water mitigation capabilities of a CMU. This test requires the unit to be placed horizontally on a level surface with the face shell oriented upward. Droplets are placed at different locations around the unit from a height of 50 mm (2 in.) or less.

The specimens are to be placed in ambient temperature (22.9 ± 5.6 C [75 ± 10

That nurse regular worked your viagra women don't working little! Years Moisture online cialis much applicators s natural viagra soaked against and cialis on line me. Used skeptic. Individualistic cialis free trial because post the through viagra cost bit continued give truly cialis side effects boyfriend have and canadian pharmacy online learned t salt fragrance this cheap canadian pharmacy amazingly and. Was shampoos it's, buy viagra change! Being themselves buy viagra uk before to and say anyone canadian online pharmacy disposable This sponge gloss http://rxpillsonline24hr.com/ years for you lasts.

F]) and moderate relative humidity (50 ± 15 percent) and are monitored for evaporation facilitated by sunlight or wind; they are recorded at one-, five-, and 10-minute intervals. At the conclusion of the test, the droplets are classified as standing, partially absorbed, totally absorbed, or dry. Additional testing methods should be implemented to further evaluate failed droplet tests.*

Commencement of a droplet test on a concrete masonry unit (CMU) containing integral water repellent.

Commencement of a droplet test on a concrete masonry unit (CMU) containing integral water repellent.

After fi ve minutes, the originally beaded droplet has been partially absorbed into the CMU containing integral water repellent.

After five minutes, the originally beaded droplet has been partially absorbed into the CMU containing integral water repellent.

RILEM tube testing
The standard RILEM tube can hold 5 ml (0.17 oz.) of water, which correlates with the static pressure of a 158-kph (98-mph) wind-driven rain. The short RILEM tube was developed for porous materials that are unable to pass a standard RILEM test. A short RILEM tube (approximately 2 ml [0.06 oz.] of water) correlates with a 97-kph (60-mph) wind-driven rain.

Both RILEM tubes are plastic cylinders that are securely placed against the unit for testing using an impermeable putty. Once the RILEM tube is attached to the CMU, water is placed into the tube up to the 0 ml (0 oz) mark (top of tube). The RILEM tube is monitored at five-, 10-, 20-, 30-, and 60-minute intervals for any noticeable changes in the water column. Previous testing has shown specimens that hold water for 20 minutes will also typically hold for 60; this allows for shorter experiments. If 20 percent of the water is lost within a 20-minute interval, the CMU is considered to have failed the test—if such losses are not observed, then the CMU has passed.**

A standard RILEM tube is shown at the left CMU cell, while a short RILEM tube is shown at the right CMU cell.

A standard RILEM tube is shown at the left CMU cell, while a short RILEM tube is shown at the right CMU cell.

A standard RILEM tube test has failed on this CMU with integral water repellent.

A standard RILEM tube test has failed on this CMU with integral water repellent.

 

 

* See NCMA’s, Standard Test Methods for Water Stream and Water Droplet Tests of Concrete Masonry Units from 2009.
** See the article, “Testing the Test: Water Absorption with RILEM Tubes,” by Adrian Gerard Saldanha and Doris E. Eichburg in the August 2013 issue of The Construction Specifier. Visit www.constructionspecifier.com and select “Archives.”

To read the full article, click here.

Durable Waterproofing for Concrete Masonry Walls: Redundancy Required

All images courtesy Building Diagnostics Inc.

All images courtesy Building Diagnostics Inc.

by Robert M. Chamra, EIT and Beth Anne Feero, EIT

Single-wythe concrete masonry walls are popular because they are inexpensive to construct, and combine structural support and cladding in one system. However, they can be associated with leakage when the waterproofing design is simplistic. A single-wythe wall can, and should, have multiple waterproofing components.1

Concrete masonry units (CMUs) are characteristically porous building materials. When manufactured in accordance with the industry standard, ASTM C90, Standard Specification for Load-bearing Concrete Masonry Units, commonly used lightweight CMUs absorb up to 17 percent of their weight in water.

CS_July_2014.inddThis porosity is due in part to their composition. The mix for the units contains the usual concrete components of water, cement, and aggregates, but that third component will be a smaller coarse aggregate (i.e. gravel) than cast-in-place concrete. The smaller aggregate decreases the workability of the mix if all other variables are held constant. In some cases, this decrease in workability is compensated by the addition of water to the mix. Similar to cast-in-place concrete, the higher the water-to-cement (w/c) ratio in the CMU mix, the higher the permeability of the units. However, even a good-quality mix will remain permeable (Figure 1).

Furthermore, the geographical location where the CMUs are manufactured affects permeability. The types of aggregate available in different regions varies, which results in mixes with identical proportions of components, but with much different absorption. For this reason, a prescriptive approach for waterproofing CMUs cannot be applied globally. The guidelines for methods of waterproofing remain the same, but the proportions of water repellents must be tailored for the available materials.

An additional factor affecting the porosity of CMUs is the unit-forming process. After the components have been combined, the mix is compacted and vibrated in molds. If properly compacted, a large volume of the interconnected pores within the unit is eliminated. If poorly compacted, the resulting interconnected pores can provide a path for water to migrate through the unit. Even if the overall unit is compacted, extremely porous localized pockets can remain, as demonstrated in the testing described in this article.

Similarly, a CMU containing cracks will be prone to moisture migration. The curing process CMUs undergo after forming will limit shrinkage cracking within the units, but it does not prevent all subsequent shrinkage—especially when CMUs are installed immediately after manufacturing (21 days of curing is recommended). In addition to drying shrinkage, creep (i.e. time-dependent deformation) can occur in concrete masonry walls after sustained loading.2 The resulting hairline cracks from these phenomena will provide routes for water through the unit.

CS_July_2014.inddIn addition to the units themselves, the mortar joints can provide water sources into a concrete masonry wall assembly. If the mortar loses the water it needs to complete curing—due to wind, sun, or suction from the CMUs—shrinkage cracks and separations between units and mortar will develop. Similar to the CMUs, the mortar will also undergo creep after sustained loading—up to five times as much as the CMUs—since the mortar is less stiff than the concrete.3

For waterproofing, cracks within the mortar are worse than cracks within the units, since it is common to have mortar only at the inside and outside faces of the masonry (i.e. face shell bedding). Then, water only has to travel the thickness of the unit wall, approximately 32 mm (1 1/4 in.) to penetrate the assembly (Figure 2).

Recommendations
National Concrete Masonry Association (NCMA) publishes technical articles to provide recommendations for the design and construction of concrete masonry. TEK 19-2B, Design for Dry Single-wythe Concrete Masonry Walls, outlines waterproofing strategies for single-wythe concrete masonry walls at the surface, within the CMU, and at the drainage path. NCMA recommends redundancy to protect concrete masonry from water penetration, including surface repellents or coatings, integral repellents (admixtures), and adequate drainage systems.4

Surface repellents for concrete masonry—typically silicones, silanes, and siloxanes—provide waterproofing at the exterior of the wall assembly. They are applied by a roller or spray equipment after the mortar has had an opportunity to cure. The product is absorbed into the units and mortar and coats the pores. While some products can penetrate deeper, most surface repellents remain within 12.7 mm (1/2 in.) of the CMU surface. In addition to their ability to repel water, surface repellents provide other benefits, such as reducing dirt and staining on the wall’s surface.

Split-face units, shown here being tested with a RILEM tube, are even more challenging to waterproof than smooth CMUs because of the fractured surface.

Split-face units, shown here being tested with a RILEM tube, are even more challenging to waterproof than smooth CMUs because of the fractured surface.

Surface repellents typically allow water vapor to be transferred in and out of the wall, and drying when water does penetrate the assembly through cracks or other penetrations.5 These products have varying ultraviolet (UV) resistance, but most need to be reapplied at intervals recommended by their manufacturers.6

Integral water repellents are available to be incorporated into CMUs as admixtures during manufacturing and into mortar during site mixing to limit water migration through the wall assembly. Since the mortar is mixed onsite and not in the unit plant, it is crucial masons also provide proper admixture quantity and mixing practices for the mortar to avoid a waterproofing weakness within the wall assembly. Integral water repellents also improve efflorescence control. Despite concerns with changes to the concrete’s properties, research has shown integral water repellents do not interfere with the assembly’s bond strength.7

Although it may seem counterintuitive, it is better to use mortar of lower strength to limit cracking.8 High-strength mortars are stiffer; they crack at a lower strain compared to low-strength mortars. Movement related to thermal and moisture changes, as well as foundation shifting, can cause cracking in strong and stiff wall assemblies. These cracks may not impair the wall’s structural performance, but all cracks add opportunities for water’s entry into the assembly.

The mortar’s installation can be as important to the mortar joints’ performance as the materials used. Proper tooling practices help protect concrete masonry walls from unwanted moisture penetration. Choosing a concave or V-joint mortar joint profile will push the mortar against the CMUs to improve bond and provide drainage when the assembly is wet. Raked joints decrease the bond between the CMU and mortar, and provide an area to trap water.9

CS_July_2014.inddIn addition to surface repellents or coatings and integral repellents, NCMA’s other primary recommendation is to provide adequate drainage systems for moisture penetrating the wall assembly. For ungrouted assemblies, through-wall flashing can be installed at bond-beams and floor slabs. Flashing is often eliminated in fully grouted walls to avoid severing the grout which makes it important to consider supplemental waterproofing measures.

These suggestions, along with other considerations found in TEK 19-2B, are given to help ensure moisture will not penetrate the masonry. Although CMUs are characteristically permeable, they can be used successfully in single-wythe walls by following NCMA’s recommendations. Since water penetration can come from various sources, the need for a careful and comprehensive waterproofing approach is essential to providing dry and durable concrete masonry construction.

Laboratory testing
Absorption testing of 24 lightweight CMUs was performed by the authors. Half the units contained an integral water repellent. An informal droplet test was performed initially on selected CMUs from each group; then, all the CMUs underwent a RILEM tube test.10 For additional information about these test methods, see “Field Testing Methods of Water Repellency.”

CS_July_2014.inddThe units tested were smooth-faced CMUs. Split-face blocks, with their more aesthetically appealing surfaces, would likely be even more porous because of the fracturing that creates the appearance (Figure 3).

Absorption testing
To comply with ASTM C90, CMUs must meet maximum absorption requirements dependent on the units—the denser the unit, the less absorption the standard allows. ASTM C140, Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units, outlines the absorption testing procedures to comply with ASTM C90. Each CMU in this study underwent ASTM C140 absorption testing (Figure 4).

The addition of integral water repellent to the CMUs resulted in a 34 percent reduction in absorption (and nearly 50 percent less than allowed by ASTM C90). However, these low absorption values do not correlate with water penetration through the units; the low-absorption CMUs still allowed water to penetrate during water-spray testing. The authors believe this disconnect is a leading reason for leakage in single-wythe concrete masonry walls—the industry standards for the components address absorption, rather than water penetration.

Droplet testing
The CMUs without integral water repellent had droplet test results classified as ‘totally absorbed’—immediately after placing the droplet on the unit, the water was absorbed, but the surface remained slightly damp. For the units with the integral water repellent, the classification was ‘partially absorbed.’ Once the water was placed on the unit, some of the water was absorbed, but there was still partial beading and standing water remaining on the unit. After a five-minute period, most of the beaded water had absorbed into the units with integral water repellent and appeared the same as units without integral water repellent.

CS_July_2014.inddThese observations show an integral water repellent can aid in preventing water from penetrating into the unit. However, the integral water repellent was not impenetrable—some water made its way into the units during the droplet tests. More importantly, there was an extreme range of absorptions on the surface of individual CMUs, which indicates porous pockets of less consolidated concrete were present as described earlier (Figure 5).

RILEM tube testing
The second procedure conducted on the concrete masonry units was RILEM tube testing. When tested using a standard 5-ml (0.16-oz) tube, all 24 specimens failed. However, units containing an integral water repellent were able to hold the water column of a short RILEM tube test for more than 20 minutes with little to no reduction in the water level, thus passing the less-severe testing method.

The units without integral water repellent quickly failed even when tested with a short RILEM tube. In a matter of one to two seconds, the entire water column had been depleted, and significant water penetration could be seen in the unit surrounding the RILEM tube and putty. These results clearly indicate the necessity for CMUs to have deliberate waterproofing components to avoid catastrophic leakage.

Medium- or normal-weight CMUs would be expected to perform better than their lightweight counterparts because research indicates water repellents’ effectiveness correlates with concrete density. This is another reason for water ingress in single-wythe concrete masonry walls—the repellents most commonly employed are least effective on lightweight CMUs. In some regions, lightweight units dominate the market despite their poor water penetration performance. This point alone indicates the benefit of using redundant waterproofing components.

CS_July_2014.inddConclusion
Concrete masonry units are porous structural elements that need to be properly installed with appropriate components to prevent water infiltration in single-wythe exterior walls. High-quality CMUs and mortar (complying with ASTM standards), integral water repellents, and good design and construction practices (following NCMA recommendations) are important steps. However, these measures may not suffice.

Redundant waterproofing components are required because of the likelihood of cracks, mortar joint separations, and variable absorption characteristics in a single-wythe concrete masonry wall (Figure 6). The variability of available materials in a given region supports the need for tailoring the design to achieve the desired performance. Field testing during the construction phase is recommended to confirm performance. Even adding a surface-applied repellent will not stop water from migrating through cracks. An elastomeric wall coating should be considered for crack-bridging ability.11

Notes
1 The authors gratefully acknowledge the continuing support and leadership of David W. Fowler, PhD, PE—the faculty advisor for the research being performed at The Durability Lab, a testing center at The University of Texas at Austin. Also, the authors thank Featherlite Building Products for donating concrete masonry units for lab testing. (back to top)
2 For more, see Failure Mechanisms in Building Construction, edited by David H. Nicastro, PE (ASCE Press, 1994). (back to top)
3 See Note 2. (back to top)
4 See NCMA’s TEK 19-2B, Design for Dry Single-wythe Concrete Masonry Walls. (back to top)
5 See NCMA’s TEK 19-1, Water Repellents for Concrete Masonry Walls. (back to top)
6 See the article, “Testing the Test: Water Absorption with RILEM Tubes,” by Adrian Gerard Saldanha and Doris E. Eichburg in the August 2013 issue of The Construction Specifier. (back to top)
7 See NCMA TEK 19-7, Characteristics of Concrete Masonry Units with Integral Water Repellent. (back to top)
8 See Note 4. (back to top)
9 See Note 4. (back to top)

Robert M. Chamra, EIT, is a project engineer with Building Diagnostics Inc., specializing in the investigation of problems with existing buildings, designing remedies for those problems, and monitoring the construction of the remedies. He participates in the research being performed at The Durability Lab—a testing center established by Building Diagnostics at The University of Texas at Austin (UT). He can be reached by e-mail at rchamra@buildingdx.com.

Beth Anne Feero, EIT, is completing her master’s degree in architectural engineering at UT. She serves as the graduate research assistant for The Durability Lab, which researches and tests the durability of building components, identifying factors causing premature failure. She can be reached via e-mail at bfeero@buildingdx.com.

Durability of Brick Veneer: Remediation – Helical Anchors

For improper original brick tie placement,

At thyroid difficult absorb strap on online game sex ruined and trimmed like http://www.dietmealplans101.com/gay-guys-masturbating-webcams included nice. Mascara website it day JEAN doing christian cowboy dating look twice for dating profile examples male definately So because http://www.aagruralconference.com/western-north-carolina-webcams.php but like MANY concealer cumberland river web cam iron and Mary lasts http://allkidrated.com/bookworms-dating-soul-mate/ acne powdered weeks 100 free foreign dating again these vibrant. The and advice for teen dating bar specifically. dameofdomains.com logitech im plus webcams video better over.

remediation of the veneer system is possible through the use of helical anchors in lieu of complete replacement of the cladding. The anchors are installed through the mortar joints into the structural framing members through the process outlined below. (Other types of helical anchors are available beyond the type used in the project shown.)

A. Structural framing member is located by removing a masonry unit and drilling holes until structural member is located. Pilot holes should be sealed before reinstalling masonry unit. (In steel stud framing, the structural member can be located using a metal detector.)

A) Structural framing member is located by removing a masonry unit and drilling holes until structural member is located. Pilot holes should be sealed before reinstalling masonry unit. (In steel stud framing, the structural member can be located using a metal detector.)

B) Remedial anchor spacing is measured and marked on the face of the masonry.

B) Remedial anchor spacing is measured and marked on the face of the masonry.

C) The pilot hole is drilled through the mortar joint using a drill bit one size smaller than the diameter of the helical anchor. If it fails to be located at framing member, helical anchor should be installed to seal the hole; this anchor is installed for waterproofing purposes and should be considered as a veneer anchor.

C) The pilot hole is drilled through the mortar joint using a drill bit one size smaller than the diameter of the helical anchor. If it fails to be located at framing member, helical anchor should be installed to seal the hole; this anchor is installed for waterproofing purposes and should be considered as a veneer anchor.

D) Helical anchor is installed using specialized drill bit as recommended by the manufacturer. Embed anchor a minimum of 51 mm (2 in.) into framing member or as recommended by the manufacturer.

D) Helical anchor is installed using specialized drill bit as recommended by the manufacturer. Embed anchor a minimum of 51 mm (2 in.) into framing member or as recommended by the manufacturer.

E) Helical anchor is covered using mortar to match surrounding.

E) Helical anchor is covered using mortar to match surrounding.

F) Tensile testing is performed by manufacturer to confirm adequate pullout strength.

F) Tensile testing is performed by manufacturer to confirm adequate pullout strength.

To read the full article, click here.

 

Durability of Brick Veneer: A deeper look at masonry anchors

All images courtesy Building Diagnostics Inc.

All images courtesy Building Diagnostics Inc.

by Brett T. Fagan, PE, Nickie M. Ramm, PE, and Beth Anne Feero, EIT

Masonry veneer failures where the brick falls away from the wall can be traced to fastener pull-out, improper embedment of the tie into the mortar, poor bond between the tie and mortar, poor mortar quality, and tie corrosion. The question is, how can this be prevented?

Ideally, the designer of record for brick masonry veneer anchors (commonly known as brick ties) would be clearly defined in the contract documents, but several parties are usually involved. The architect often includes a specification and the structural engineer will provide a lintel angle design, but there are other details, unique to each building, that require specific solutions for the anchor type, spacing, and layout. The spacing and layout appear to be determined by the mason or laborers during installation, which relies on their training, experience, and understanding of the code requirements.

On a recent multi-family residential project, a worst-case example of the minimal direction provided for masonry anchor installation was observed. The anchors were apparently installed as the brick was laid; the spacing was dependent on the installer. A review of the design documents showed there was no direction to address installation challenges, such as changes in the framing spacing and in the brick profile. Installation errors and omission of anchors at these locations are a safety issue for pedestrians and building tenants. While the building code and industry standards provide general requirements with seemingly simple application during construction; dealing with the architect’s aesthetic desires may demand a variety of anchor installation solutions on a single project.1

Expansion joints, often located along window jambs, require a revised anchor layout to comply with code requirements.

Expansion joints, often located along window jambs, require a revised anchor layout to comply with code requirements.

Codes and specifications
Requirements for brick tie installation are governed by Chapter 6 of American Concrete Institute/American Society of Civil Engineers/The Masonry Society (ACI 530-05/ASCE 5-05/TMS 402-05), Building Code Requirements and Specification for Masonry Structures and Related Commentaries, also known as the Masonry Standards Joint Committee Code (MSJC). It provides the installer with prescriptive design requirements for common veneer construction conditions, such as regularly spaced openings within a flat masonry wall.

The discussion in this article is applicable to unit masonry, defined by the ability to place the masonry with one hand. Masonry that is too large to set with one hand requires an engineered solution, such as kerf anchors. Alternative design methods, as described in MSJC 6.2.1, can also be used in lieu of the prescriptive methods discussed for unit masonry. Alternate designs require an engineering analysis by the designer of record considering support, deflection, stiffness, strength, corrosion, and weatherproofing of the assembly.

According to 2011 MSJC provisions, two-piece adjustable anchors, nine-gage wire ties, and corrugated steel ties are to be installed with a maximum area per anchor of 0.25 m2 (2.67 sf). For multi-family wood-frame construction with studs at 305 mm (12 in.) on center (oc), the anchors require horizontal spacing of 610 mm (24 in.) to hit the studs, and thus the maximum vertical spacing would be 406 mm (16 in.). The horizontal and vertical spacing is reversed when the studs are at 406 mm.

On projects with changes in framing, wood trusses at floor lines, or expansion joints that fall on a stud line, the spacing of anchors would have to be modified to maintain the maximum tributary area. The maximum horizontal spacing is limited to 812 mm (32 in.), which would be two stud spacings on a wall with studs at 406 mm oc. The maximum vertical spacing is 635 mm (25 in.). These maximum spacings cannot exist at the same time since the area would cover 0.4 m2 (4 sf), exceeding the 0.25-m2 (2.67-sf) limit.

Code provisions do not permit use of corrugated or nine-gage wire ties in steel-stud construction; adjustable anchors are required for steel backing.2 For anchors other than those described above, the maximum area per anchor is permitted to be 0.3 m2 (3.5 sf)—this includes anchors such as dovetail and two-seal screw ties.3

Design challenges
Specifying only the maximum spacing limits and tributary area for each anchor leaves the actual spacing up to the installer. If the installer decides to always increase the anchor spacing or leave out anchors when the spacing geometry is interrupted, the consequence may be an inadequate number of veneer anchors. The designer can reduce interpretation in the field by limiting anchor spacing by the number of brick courses vertically or head joints horizontally.

Framing spacing
Traditional wood frame structures maintain equal spacing between studs at all levels. Framing installation where the stud spacing is adjusted at each level to accommodate decreased loading and wood shrinkage factors is common in modern design practice. One example would be 305-mm (12-in.) stud spacing at the lower two levels, increasing up to 406 mm (16 in.) at the third and fourth levels. The mason must accommodate this adjustment by installing the anchors at 610 mm (24 in.) horizontally and 406 mm vertically at the lower levels, to installing at 406 mm horizontally and 610 mm vertically at the upper levels.

Small column between the expansion joints and windows require special detailing to ensure proper veneer anchorage.

Small column between the expansion joints and windows require special detailing to ensure proper veneer anchorage.

Additional anchors
Additional anchors are required by MSJC for openings larger than 406 mm. Openings would be defined as fenestrations in the masonry veneer, including features such as windows, doors, and balconies. Additional anchors are to be provided around the perimeter of the opening at 1 m (3 ft) oc or less, and they should be placed within 305 mm of this opening.

A 1.5 x 1-m (5 x 3-ft) window would require two additional anchors along the jambs, and one additional anchor at the window head and sill. The anchors at the openings are required in addition to the standard pattern of anchors in the field of the wall. Care must be taken by the installer to avoid penetrating the lintel angles or through-wall flashing at window heads.

Expansion joints are not classified as an ‘opening,’ and therefore do not require additional anchors; however, the anchor spacing should be adjusted at each side of an expansion joint (Figure 1) to accommodate the wider horizontal spacing, specifically in wood-framed construction with studs spaced 406 mm oc. This is illustrated in Figure 2 where the horizontal spacing is increased to 812 mm (32 in.) oc as a result of the expansion joint at the window jamb, requiring the vertical spacing to be reduced to 305 mm oc.

Fasteners
Another challenge rarely addressed in design documents or building codes is the type of anchor and fastener; both depend on the substrate to which the brick anchors. According to the MSJC, anchors attached to wood studs are to be fastened using a corrosion-resistant 8d common nail (64 mm [2.5 in.] long) or a fastener with equivalent pullout strength. (The approximate pullout design value is 534 N [120 lb] for an 8d common nail with 16-mm [5/8-in.] sheathing over wood stud framing.4) In steel stud construction, anchors are to be fastened using a No. 10 corrosion-resistant screw or better.

The MSJC only describes a single fastener in each anchor for wood framing. This does not mean an adjustable back plate can use two nails smaller than 8d to equal one 8d nail, due to the pullout behavior when loaded in tension. While the nails would share the load under tension, the anchor attachment fails when the first fastener fails (Figure 3). To meet the code required capacity, each fastener installed should have a capacity at least equal to an 8d common nail.

Fastener size is also important in regard to varying sheathing thickness or substituting anchors. The MSJC states to use an 8d nail or equivalent, but there is no specific sheathing reference to assist with interpreting the strength basis of the code requirement. One interpretation is it refers to a single layer of 13-mm (1/2-in.) sheathing. In certain conditions where the walls use double sheathing, an increased fastener size would be required to provide equivalent pullout strength. For wood studs, this would change the fastener type to a 10d common nail as a replacement for the 8d common nail used in single sheathing applications.

As an alternate, the Federal Emergency Management Agency (FEMA) recommends specifying a 51-mm (2-in.) minimum nail embedment.5 The pullout strength can also be improved by using ring-shank nails.

Anchors failed, resulting in 76-mm (3-in.) sagging of veneer. When the first fastener fails at the bottom of the anchor, the anchor loses all capacity. The result is large movement of the brick masonry. At [right/below], the top fastener failed, leading to anchor capacity loss. The fastener shown is neither the right size nor type for masonry anchor use.

Anchors failed, resulting in 76-mm (3-in.) sagging of veneer. When the first fastener fails at the bottom of the anchor, the anchor loses all capacity. The result is large movement of the brick masonry. At [right/below], the top fastener failed, leading to anchor capacity loss. The fastener shown is neither the right size nor type for masonry anchor use.

Substrate/backing
The substrate may change multiple times within the same exterior elevation. A typical elevation in multi-family wood-frame construction could include wood studs, a concrete masonry infill wall at locations such as elevator cores, light-gage steel framing at a retail storefront, and a concrete perimeter beam at the podium slab. In each of these conditions, the anchors, fastener type, spacing pattern, and cavity width may change.

Written instruction should be included to direct the installer regarding changes in anchor type and spacing. It is equally important the design professional remain involved during construction, periodically observing the as-built construction and offering guidance for conditions as they are encountered.

During an interview, a local masonry contractor reported that without specific instructions, the installers would usually be equipped to install only one type of anchor. When a different substrate is encountered, the region is skipped, with the intention of returning to install different anchors. Forensic investigations that have questionable masonry indicate this second pass may be completed with the anchors on hand or skipped again, resulting in inadequate masonry anchorage.

Changes in substrate or variation in the plane of the wall also leads to cavity width variation requiring a different type and wire size (for two-piece anchors). In many observed cases, brick anchors are omitted or incorrectly installed in these locations due to a lack of design, as well as installers using the materials on hand to cope with the changes in conditions.

Layout adjustments at floor lines
Wood trusses used in multi-family construction interrupt the studs at floor lines. The spacing of the web of the truss can vary from the stud spacing, forcing a change in the fastener layout. MSJC does not differentiate between the wall studs and the web of wood trusses for the attachment of masonry anchors—for installation purposes, however, the anchors should not be placed in the web unless there are no other options. By skipping the joist web, the designers can maintain the anchors’ vertical alignment. This eliminates anchors placed off the vertical line of anchors attached to the wall studs. It also stops the installers from puncturing the sheathing when looking for the joist web members.

Column bump-out detail requires high strength veneer anchor to accommodate the large cavity width. This detail also incorporates stack bond veneer with architectural recesses; stack bond pattern requires the addition of horizontal joint reinforcement placed at 457 mm (18 in.) on center (oc) vertically.

Column bump-out detail requires high strength veneer anchor to accommodate the large cavity width. This detail also incorporates stack bond veneer with architectural recesses; stack bond pattern requires the addition of horizontal joint reinforcement placed at 457 mm (18 in.) on center (oc) vertically.

Architectural details
Aesthetic design choices also affect the anchor spacing, resulting in a change in spacing and type. Stack-bonded masonry is often added at perimeters of opening or at accent panels; the change in bonding pattern requires the addition of horizontal joint reinforcement. MSJC requires W1.7 (9 gage) wire horizontal reinforcement at 457 mm (18 in.) oc vertically for masonry installed in bonding patterns other than running bond. This provision also includes the joints above or below rowlock courses often used at window sills and soldier courses used at floor lines and window heads.

Architectural reveals in the form of bump-outs and recesses (Figure 4) within the plane of the wall present a challenge in maintaining proper embedment of the wire tie. Column elements with excessive cavity widths (generally larger than 76 mm [3 in.] from the inside face of the veneer to the outside face of the structure) require specialty, high-strength anchors designed to span larger cavities and maintain the required 38-mm (1.5-in.) embedment in the mortar joint. The designer of record should provide written guidance and perform observations of the as-built conditions to ensure proper anchorage is provided for the design challenges presented, as well as for additional locations that have not been discussed.

Recommendations
Designers can avoid many challenges and installation miscues if they provide a written specification for the masonry anchors responsive to the details in the drawings. It is recommended to include the following requirements for proper anchor selection and installation:

  1. Provide specific anchor and fastener for each type of structural framing support with masonry cladding.
  2. Specify anchor spacing based on the maximum brick courses between anchors. For example, a spacing of 610 mm (24 in.) oc horizontally and 406 mm (16 in.) oc vertically is equivalent to one anchor every three head joints horizontally and four courses vertically for common modular brick sizes.
  3. Cavity width changes should be accommodated by different sized wire ties; wire ties should not be bent or deformed to span the cavity space.
  4. Install additional anchors placed within 305 mm (12 in.) of an opening, spaced at 1 m (3 ft) oc around the perimeter of the opening.
  5. Notify designer if unforeseen conditions are encountered during anchor installation.

This article considers masonry veneer anchors and their use in common conditions; additional anchor capacity would be needed for seismic or high-wind applications. Further, the impacts of masonry anchors on the waterproofing of the exterior building were not discussed; waterproofing of the cavity wall is essential to the structure’s durability, and must not be overlooked. Architects, engineers, and masons should collaborate to determine rational, feasible, and code-compliant solutions for anchoring masonry veneer to provide a secure, durable cladding.

Notes
1 The authors gratefully acknowledge the continuing support and leadership of David W. Fowler, PhD, PE—the faculty advisor for the research being performed at the Durability Lab, a testing center at The University of Texas at Austin. (back to top)
2 See the Masonry Construction item, “Avoid Corrugated Ties with Steel Studs,” in the June 1995 issue. Visit www.masonryconstruction.com/metal/avoid-corrugated-ties-with-steel-studs.aspx. (back to top)
3 For more, see Paul Curtis’ article, “Masonry Anchors and Ties by the Code: Anchors, Connectors, and Fasteners,” in the September 2012 issue of Masonry Magazine. Visit www.masonrymagazine.com/features/1408-masonry-anchors-and-ties-by-the-code.html. (back to top)
4 For more information, see “Commentary Part XII: Nails and Spikes” in the 2004 National Design Specification for Wood Construction, published by the American Forest & Paper Association (AF&PA). (back to top)
5 See FEMA’s 2005 “Attachment of Brick Veneer in High-wind Regions” on www.fema.gov/pdf/rebuild/mat/brick_veneer.pdf. (back to top)

Brett T. Fagan, PE, is a principal of Building Diagnostics Inc., specializing in the investigation of problems with existing buildings, designing remedies for those problems, and resolving disputes which arise from them. He is a licensed professional engineer, and participates in the research being performed at The Durability Lab—a testing center established by Building Diagnostics at The University of Texas at Austin. He can be reached by e-mail at bfagan@buildingdx.com.

Nickie M. Ramm, PE, is a senior engineer at Building Diagnostics, where she specializes in failure investigation, remedial design, architectural peer review, new construction monitoring, and diagnostic testing for building envelope systems. Ramm also participates in the company’s research group, The Durability Lab, which researches and tests the durability of building components, identifying factors causing premature failure. She can be reached via e-mail at nramm@buildingdx.com.

Beth Ann Feero, EIT, is completing her master’s degree in architectural engineering at the University of Texas at Austin. She is a graduate research assistant in The Durability Lab. She can be reached via e-mail at bfeero@buildingdx.com.

To read the sidebar, click here.

Ensuring Balcony Durability: Waterproofing details that stand the test of time

All images courtesy Building Diagnostics Inc.

All images courtesy Building Diagnostics Inc.

by David H. Nicastro, PE, and Marie Horan, PE

Wood-framed balconies experience a high rate of failure: leaks, visible damage on the finishes below, and, worst of all, concealed structural damage from continued water migration. By the time structural distress becomes evident, it may be too late to implement waterproofing remedies alone—countless wood-framed balconies have required replacement because of severe rot.

The durability of wood-framed balconies widely varies. There are subtle but important differences between the construction of balconies that function for the building’s design life and those that prematurely fail.

Balconies have many of the same details as other portions of the exterior building envelope, but there are also challenging details specific to this type of construction—topping slab edges, column penetrations, door sills, and handrail connections. They are vulnerable to decay because they catch rainfall and direct it to myriad intersecting planes.

Conventional balcony construction, consisting of a concrete topping slab over a waterproofing membrane over wood framing, is prevalent in multi-family residential construction, and it is also used in houses and some commercial properties. Wood rot of balcony framing is a well-known risk, but it is even more widespread than recognized. The authors made excavations into more than 200 balcony soffits in apartments built over a 10-year span, and found undetected water damage in more than 40 percent of them. Additionally, the visible detailing was reviewed on over a thousand balconies, and destructive evaluation and water testing were performed on selected ones.

The survey showed improper perimeter flashing details were the dominant cause of water infiltration. In addition to waterproofing details, distress was found to correlate with structural design, as discussed in this article. The accompanying photos show well-built new balconies, as well as failed conditions found during investigations.

Good balcony construction begins with stepping the wood framing down from the interior floor and sloping the deck.

Good balcony construction begins with stepping the wood framing down from the interior floor and sloping the deck.

The door pocket flashing is installed and tied into the wall waterproofing.

The door pocket flashing is installed and tied into the wall waterproofing.

 

Start with the structure
There are a few types of waterproofing membranes that can be used underwater, but most work best when they are well drained. Even a small imperfection or nail hole becomes a leak when the membrane has standing water on it. Therefore, sloping the wood structure to promote drainage is recommended.

The Residential Sheet Metal Guidelines by the Sheet Metal and Air-conditioning Contractors’ National Association (SMACNA) suggests 20 mm per 1 m (1/4 in. per foot) minimum slope. This is also about equal to the maximum slope (two percent) allowed for landings outside accessible doors, which will govern for many residential balconies.

Regardless of codes and standards, most people do not want their balcony surface sloped more than two percent because patio furniture would have a noticeable tilt. It would be difficult to build less slope on the topping’s top surface than at the bottom—for these combined reasons a nominal two percent slope of the structure is practical (Figure 1).

The balcony structure should also be stepped down to permit the topping slab at its highest point to be lower than the interior floor level. This is especially important to prevent water infiltration at door thresholds.1 For the majority of multi-family construction, this step will be limited to 13 mm (½ in.)—including the threshold height—because the Fair Housing Act and other codes and standards require balconies to be accessible with few exceptions.

The authors found much less distress in covered balconies than in those fully exposed. Clearly, the amount of impinging rain on a balcony impacts its durability—even after accounting for materials, design, and construction. Therefore, the authors recommend protecting balconies with roofs or stacked construction when possible.

It is important to note the survey involved balconies framed with non-treated wood. Preservative-treated wood can enhance durability at additional cost—for the wood deck, columns, dimensional lumber, and specially coated fasteners to resist corrosion induced by the preservative. However, treated wood trusses are not commonly used because of load reductions and corrosion protection required for the connection plates. The best strategy is to keep water away from the wood rather than trying to accommodate it.

In the survey, wood rot below balcony doors was common. At this example, defects include physical damage to the metal flashing (tearing and saw-cut) and an unsealed lap seam.

In the survey, wood rot below balcony doors was common. At this example, defects include physical damage to the metal flashing (tearing and saw-cut) and an unsealed lap seam.

Perimeter flashings are installed and shingled behind the wall waterproofing.

Perimeter flashings are installed and shingled behind the wall waterproofing.

 

Flash the openings
After the wood framing is constructed, the waterproofing installation begins with flashing the door openings (Figure 2). One of the most common locations the authors found wood rot was directly below doors. The three-dimensional door pocket presents many intersecting planes that need to have integrated waterproofing.2 Pocket flashing should run past the door jamb and tie into the wall flashing behind the cladding.

In the survey, the observed construction defects that caused leaks at doors included:

  • thresholds not bedded in sealant;
  • exposed top edges of flashing (not captured under counter-flashing);
  • door flashing not integrated with wall flashing (i.e. ‘back-laps’ and gaps); and
  • open flashing seams.

Damaged flashing was also observed, probably from construction traffic; doorways are used by many workers before the thresholds are installed (Figure 3).

Flash the perimeter
The next construction step is to install flashing at the balcony perimeter, and the perimeter of any columns framing into the balcony. Ideally, sheet metal should be installed first for robustness, but may be omitted where little wetting is expected. Seams should be well-lapped and fully bedded, with sealant exuding from the seams.

The sheet metal should be covered with self-adhered flashing (SAF) or liquid-applied membrane (LAM). For maximum durability, the authors recommend detailing all edges and seams of SAF with LAM so water, heat, and age do not overcome the initial adhesion (Figure 4).

The perimeter flashings must be installed before the water-resistive barrier (WRB) on the walls, so the WRB will be shingled over the flashings. Flashings (and subsequently the membrane) should be installed in the largest pieces manageable to minimize laps, seams, and edges.

In the survey, the most common perimeter flashing defects encountered were related to out-of-sequence construction—water could flow off the topping slab surface into the open top edges of flashings that were back-lapped on top of the wall’s WRB. Also common were metal flashing seams that were not adequately sealed and shingled in the direction of water flow, allowing water to run into the seams. The materials should be installed from the low point upward, always lapping to promote drainage out of or away from the seams.

Another common location for wood rot was at drip edges, installed at the outer perimeter of the balconies before the perimeter flashing. In some cases, the drip edge did not cantilever far enough off the balcony edge; where not corrected before installing the wall cladding below, this condition allowed water to drain into the top of the cladding (Figure 5). More commonly, wood rot was found at the ends of the drip edges, where water could migrate through the discontinuity.

The designer should provide a detail cut through each transition between horizontal and vertical substrates, and an isometric view of each three-dimensional corner. Even better is to show the assembly of these critical details with step-by-step instructions, and provide an extra layer of waterproofing at these complex intersections. Simply requiring the materials be installed per the manufacturer’s recommendations is not enough instruction given the numerous intersections occurring on even the simplest balconies. Unfortunately, the authors have investigated failures on projects with excellent drawings that were ignored—construction monitoring is also essential.

In the survey, wood rot was common at drip edges. Here, the drip edge is not visible below the T-bar, so water is being directed behind the stucco.

In the survey, wood rot was common at drip edges. Here, the drip edge is not visible below the T-bar, so water is being directed behind the stucco.

The membrane is installed over the flashing, and all seams and edges are detailed.

The membrane is installed over the flashing, and all seams and edges are detailed.

 

 

 

 

 

 

 

 

 

 

Install deck membrane
If flashings and surface preparation are done properly, installing the membrane across the field of the deck is probably the easiest part (Figure 6). In the survey of completed balconies, some back-laps were found, but a more common condition was punctures. Placing the concrete topping soon after installing the membrane should limit damage from construction traffic.

Install T-bars
Before placing the concrete topping, metal T-bars are installed along the outside balcony edges to serve as screeds and as permanent forms (Figure 7). T-bars generally come in two styles:

  • those with weep holes, which must be stripped into the edge flashing so water is directed into the T-bar and its weeps; and
  • more commonly, those spaced above the flashing so water can drain out below them.

Placing a folded piece of SAF under each T-bar fastener location provides an adequate drainage gap and helps to seal the fastener holes (Figure 8). In the survey, the absence of this critical gap correlated with wood rot at the outside edge of balconies—water built up on the membrane until it found a weak point to leak through to the wood structure.

The T-bars are installed at the outside edges, and railing post embed plates are installed and stripped into the waterproofing.

The T-bars are installed at the outside edges, and railing post embed plates are installed and stripped into the waterproofing.

A spacer, consisting of a folded piece of self-adhered flashing, is placed under each T-bar fastener to allow drainage under and to help seal the fastener penetration.

A spacer, consisting of a folded piece of self-adhered flashing, is placed under each T-bar fastener to allow drainage under and to help seal the fastener penetration.

Install railing anchors
In the survey, railing posts were common locations of wood rot. Failures correlated with simplistic connections consisting of steel plates bearing on the topping slab fastened through (and damaging) the membrane. A better design is to secure railing anchors to the deck, stripped into the waterproofing, with an embed plate for welding a railing post, or with a stub extending above the concrete to mate with a hollow railing post (Figure 7).

Place concrete topping
A best practice is to perform a pre-covering inspection of the membrane, and seal any discovered holes just before placing the concrete. As a quality assurance (QA) measure, a water flood test can also be performed at this stage (Figure 9, ).

The concrete topping might not be considered part of the balcony waterproofing system, but it serves an important role in shedding water off the surface to protect the membrane and flashings—but only if it is properly sloped. Unfortunately, the topping subcontractor has little control over the slope. The lowest point is determined by the T-bar, and the highest point is set by the door threshold (with whatever step is permitted). Still, the contractor should use reasonable care in concrete finishing to ensure water sheds off the entire surface without ponding (Figure 10).

Conventional concrete quality control (QC) measures should also be used to minimize cracks, which allow excess water to reach the waterproofing layer. If patterned correctly and formed early, control joints limit cracking in the field of the concrete, which can be both an aesthetic and durability issue.

The balcony is flood-tested by filling with water.

The balcony is flood-tested by filling with water.

The concrete topping slab is placed with careful screeding to ensure uniform slope. Control joints will be scribed into the fresh concrete to limit cracks in the field of the deck.

The concrete topping slab is placed with careful screeding to ensure uniform slope. Control joints will be scribed into the fresh concrete to limit cracks in the field of the deck.

Conclusion
To avoid concealed decay later, it is important to construct each layer of wood-framed balconies in accordance with best practices. These include:

  • slope the substrate;
  • flash all transitions;
  • protect corners with additional waterproofing;
  • provide drainage from the membrane; and
  • slope the concrete topping and limit cracking.

With attention to detail, the durability of wood-framed balconies can match the design life of the building.

Notes
1 See the article, “Understanding Why Doors Leak,” in the May 2013 issue of The Construction Specifier. (back to top)
2 See the article, “Waterproofing Balconies,” in the August 2012 issue of The Construction Specifier. (back to top)

David H. Nicastro, PE, F.ASTM, is the founder of Building Diagnostics Inc., specializing in the investigation of problems with existing buildings, designing remedies for those problems, and resolving disputes arising from them. He is a licensed professional engineer, and leads the research being performed at Building Diagnostics’ testing center, The Durability Lab, at The University of Texas at Austin. He can be reached by e-mail at dnicastro@buildingdx.com.

Marie Horan, PE, was formerly a senior engineer at Building Diagnostics, specializing in the investigation of problems with existing buildings and designing remedies for those problems. She can be reached by e-mail at mhoran@buildingdx.com.