Tag Archives: Water repellent

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

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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.

Testing the Test: Water Repellents

by David H. Nicastro, PE

Water repellents can be confusing, from the imprecise terminology (i.e. sealers versus coatings versus sealants) to the wide variety of chemistries available. There can also be a stigma associated with repellents—many consultants are concerned about negative side effects from applying a material to the outside of a porous material, potentially impeding vapor drive from the interior.

Caution is always prudent, especially with historic buildings that can be permanently damaged by wrong-headed remediation. With reasonable care, however, appropriate repellents can be selected to provide a range of benefits, including:

  • water repellency;
  • preventing mildew growth;
  • reducing efflorescence staining;
  • preventing graffiti from adhering;
  • protecting concrete from freeze-thaw damage and corrosion of embedded reinforcing steel; and
  • stopping compounds in concrete panels from leaching onto glass, where it converts into insoluble surface deposits.

Some repellents are catalyzed so they cure on any substrate (which requires masking unintended surfaces, like windows), while others require a reaction with a specific substrate to cure, such as the high pH of concrete. Some formulations deteriorate in sunlight faster than others, requiring reapplication after five to 10 years.

Several products use room-temperature-vulcanizing (RTV) silicone, diluted with a solvent; the resulting liquid with five to 15 percent solids can be considered ‘hybrids,’ falling between a typical penetrant and a film-forming coating. In addition to the benefits listed, these robust products have better durability and can be integrated with silicone sealant on challenging joint substrates, like rough aggregate precast concrete panels. Spray-applied after the joint sealant cures, testing indicates the chemically compatible silicone repellent fills micro-voids between the sealant and the aggregate that would otherwise leak.

However, these advantages come at costs—the products are more expensive than traditional repellents, they may darken substrates, and they have a strong solvent odor during application.

Although repellents are usually considered to be clear, the author’s firm has worked with manufacturers to add colored dye, including emerald green and obsidian black, to certain repellents so they can enhance the appearance of a faded façade.

David H. Nicastro, PE, is the founder of Building Diagnostics Inc., and leads the research being performed at The Durability Lab. He can be reached by e-mail at dnicastro@buildingdx.com.

To read the full article, click here.

Testing the Test: Water Absorption with RILEM Tubes

All images courtesy Building Diagnostics Inc.

All images courtesy Building Diagnostics Inc.

by Adrian Gerard Saldanha and Doris E. Eichburg

Water repellents are often applied to exterior walls to reduce absorption. A common question from building owners is, “When does the repellent need to be re-applied?” Since water repellents are clear, visual inspections are not useful to evaluate their durability. A simple field test frequently used to measure the effectiveness of water repellents is the RILEM tube. But is this widely used test reliable?1

RILEM uptake tube attached to substrate with putty, graduated from 0 to 5 ml.

RILEM uptake tube attached to substrate with putty, graduated from 0 to 5 ml.

The RILEM tube test was adopted in the United States in the early 1980s by the water repellent manufacturing industry to assess water absorption properties of walls and other substrates, with or without treatment. Simply put, the test measures the quantity of water absorbed by a particular substrate over a given time through an uptake tube. The uptake tube is sealed to the substrate with putty (Figure 1).

RILEM was an acronym for the original French name of a European organization founded in 1947 to promote scientific co-operation in the area of construction materials and structures. A RILEM technical committee developed “Test No. II.4 Water Absorption Under Low Pressure (Pipe Method)”—now commonly known as the RILEM tube test—and explained its uses in a 1980 report.2

The hydrostatic head developed by the column of water in the tube can be correlated with wind-driven rain of a certain speed. This relationship is not linear; pressure is proportional to the square of velocity, so the wind speed per 1 ml (0.04 oz) of water at the bottom of the tube is about twice that at the top of the tube.

The tubes described by RILEM in its 1980 report were shorter (98 mm [3.9 in.] from the center of the round cylinder to the top reading mark, labeled ‘0’), and were graduated from 0 to 4 cc (about 0.14 oz). The tubes readily available today are longer (about 120 mm [4.72 in.]) and graduated from 0 to 5 ml (about 0.17 oz). The 0-ml line (top of tube) correlates to 158 km/h (98 mph) and the 5-ml mark (near the bottom of the tube) correlates to 72 km/h (45 mph). Tubes have also been produced with graduations in wind speed.

Testing the test
Although widely used, there is currently no industry standard on how to perform a RILEM test. ASTM International has reported plans to develop an uptake tube test method for water repellents, but that standard is years away.3

The authors found manufacturers use different time intervals for their readings, different amounts and types of putty to attach the tubes, and different initial water fill levels. Therefore, RILEM tests were performed in a laboratory setting to assess whether those differences matter—essentially, ‘testing the test.’ The parameters included:

  • varying the initial water level;
  • constant pressure (refilling the tube during testing) versus diminishing pressure;
  • tube design—horizontal, vertical, short, and long;
  • altering the water/specimen contact surface area; and
  • different putties.

The first problem was to find a suitable substrate for repeated testing; the volume of water absorbed in a fixed time is a material property. Concrete masonry units (CMUs) were found to be too porous before treatment (and, interestingly, even after treatment with one repellent intended for CMUs). Clay paver tiles were found to be ideal specimens, absorbing water slowly but distinctly, with measurable differences before and after treatment.

Short RILEM tube, graduated in wind speed.

Short RILEM tube, graduated in wind speed.

Untreated clay tiles took an average of eight minutes to absorb 5 ml of water. To study the absorption of water over time, and to evaluate whether conclusions depended on the duration of the tests, readings were taken every minute for graphical presentation. Distilled water was used for all tests. Various repellent types were tested. (For more on this topic, see “Water Repellants”).

Varying the water level in the tubes
The original test recommendations described by RILEM permit flexibility in deciding the water level in the uptake tube based on likely rain exposure conditions and durability requirements of the substrate. This is reflected in manufacturers’ literature that recommends testing with only 3 ml (about 0.1 oz) of water in the tube for certain repellents on extremely porous substrates.

Short tubes are available for this purpose, and have essentially the same geometry as the regular tubes (Figure 2); during testing, there was no difference between the fully filled short tubes and partially filled regular tubes. However, the authors confirmed fully filled tubes drained into the clay tiles faster than the partially filled ones because the applied water pressure is greater. This can lead to erroneous interpretations about absorption when the test time is short (Figure 3).

Constant head pressure
A more severe test method is to refill the tube at regular intervals as water is absorbed by the substrate, measuring the water added. Since the higher pressure is maintained (rather than diminishing as the water level falls), more absorption would be expected to occur in the same time. This method is not commonly used in the field, but it represents one of the myriad ways this test has been modified by different users.

Horizontal tubes
‘Horizontal’ tubes (actually mounted vertically) are convenient for testing horizontal surfaces, like concrete slabs. The opening of the uptake tube is co-axial with the vertical column of water. From the authors’ testing, no significant difference was observed in the readings obtained from the two tube orientations on the same sample (Figure 4).

As shown by this graph, fully-fi lled uptake tubes drain quicker than partially fi lled tubes because of the higher hydrostatic pressure.

As shown by this graph, fully-filled uptake tubes drain quicker than partially filled tubes because of the higher hydrostatic pressure.

The absorption rate with horizontal and vertical tubes is essentially the same.

The absorption rate with horizontal and vertical tubes is essentially the same.

 

 

 

 

 

 

 

 

 

Altering the contact area
Assuming water travels through the substrate at the same velocity in all directions, the shape of the water absorbed in the substrate is initially cylindrical, and gradually approaches hemispherical.4 The geometrical boundary condition of the infiltrating water is complex and variable, and can contribute to inaccurate results.5

The contact area between the tube and surface, through which water flows into the test substrate, is bordered by putty. Larger openings lead to a higher rate of absorption as compared to smaller openings that cause a lower rate of absorption;6 therefore, putty that accidentally fills a portion of the contact area will appear to reduce the absorption. These results were confirmed by testing (Figure 5). The contact area can be recorded after the test by taking an imprint of the putty using an ink pad.7

Testing procedure recommendations
Small changes in attaching the uptake tube or performing the readings may lead to different results. The authors have the following recommendations regarding the testing.

A smaller contact area leads to lower rate of absorption.

A smaller contact area leads to lower rate of absorption.

Attaching the tubes
The supplied putty was used to attach tubes to the substrate during testing, as well as a butyl adhesive. Both adhesives worked, with similar difficulty in achieving a seal. Water leaking from the putty, instead of absorbing into the substrate, can dramatically change results (Figure 6). Therefore, it is important to watch for leaks during testing, and repeat the test if water is lost.

Both adhesives left oily stains on the substrates, the putty more than the butyl. The stains are not only unsightly, but also affect the substrate’s water repellency, and influence future repeated testing at the same location.8 It is recommended to perform an initial test in an inconspicuous area whenever possible.

Testing before and after a repellent is applied should be performed at the same locations for comparison. The same amount of putty (contact area) should be used for each test and care should be taken to ensure the opening is not covered by putty.

Filling the tubes
Air bubbles can affect results, and should be avoided. The authors found having the tip of a plastic squeeze bottle in physical contact with the back of the tube while filling it to the zero mark is the easiest way to prevent air bubbles. If air bubbles are present, the test should be repeated.

Timing
A timer should be started after the water is filled to the zero mark. The absorption that occurs before then is not usually taken into account, but it may affect the accuracy of measurements under five minutes.9

RILEM recommends readings at five-minute, 10-minute, 15-minute, 30-minute, and one-hour intervals, but also mentions in-situ measurements can be limited to the first three readings. Several repellent manufacturers require final readings at 20 minutes. In the authors’ testing, the results at 20 minutes were indicative of the results at an hour, so the longer test time does not appear to be necessary.

Even a slow drip from the putty may change results, so the test should be monitored for leaks.

Even a slow drip from the putty may change results, so the test should be monitored for leaks.

A case study on durability
To evaluate a repellent’s durability, it is essential to measure its effectiveness over time. Laboratory testing of cores removed from a treated building façade would be the most definitive method, but taking cores at intervals is expensive and disruptive. Water beading on a surface is often considered as a measure of repellent effectiveness, but it does not correlate with actual absorption (except immediately after treatment)—water can still absorb into a substrate that exhibits surface beading, and vice versa.

Field testing with RILEM tubes is a practical approach to confirming durability, and can be reliable when the variables discussed earlier are fully considered, as illustrated in a case study. A multi-story commercial office building constructed in 1989 has limestone panels cladding the lower three floors. The inferior quality limestone suffered significant erosion, discoloration, and organic growth due to high moisture absorption.

A water repellent had been applied to the limestone during original construction, but it had degraded. By the time of the study in 2001, cleaning the façade had become increasingly difficult. As the limestone eroded so easily, research and testing were required to find the least aggressive method of removing the existing sealer, dirt, and organic growth.

Several mockups were performed using various chemical and abrasive cleaning methods. The chemical cleaning was burdensome and required harsh acids. Sanding the panels was the most effective and least expensive method. Any stains that remained after sanding were removed with a biological stain remover. Following the cleaning, a clear, water-based siloxane water repellent was applied; the manufacturer provided a 10-year guarantee in 2003.

RILEM tests on limestone cladding, measuring performance of the water repellent at the same locations.

RILEM tests on limestone cladding, measuring performance of the water repellent at the same locations.

RILEM tests were performed after cleaning the limestone but before applying the water repellent. The limestone absorbed the water in the tubes within 30 minutes at all locations; three out of the five test tubes absorbed the water within 15 minutes. RILEM tests were then performed at the same locations after the water repellent was applied and cured; no water was absorbed after one hour. RILEM tests continue to be performed at regular intervals at the same locations; the last tests in September 2012 still showed zero absorption (Figure 7). The repellent will be re-applied once the limestone measurably absorbs water, indicating it is losing effectiveness.

Conclusion
Despite the range of variables that can affect results, RILEM tubes can be used reliably to test the resistance to water absorption of a substrate over time, which is the key to determining the durability of a water repellent. Locations should be selected that can be tested at regular intervals over the repellent’s service life. Results from successive tests can then be compared to indicate whether treatments are still effective or need re-application.

It is important to perform the testing in a consistent manner to get reliable results. Small changes in the testing locations, application of the RILEM tubes, or reading intervals may lead to differing results. Although there are numerous publications about RILEM tests, the authors have found no current published industry standard. Standardization should improve the uniform interpretation of results and increase the test’s use.

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. The authors also thank Fran Gale, director of the Architectural Conservation Laboratory at the University of

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Texas School of Architecture, for her technical guidance. (back to top)
2 See the 1980 report, “Tentative Recommendations: Recommended Tests to Measure the Deterioration of Stone and to Assess the Effectiveness of Treatment Methods,” by RILEM Technical Commission 25-PEM. (back to top)
3 This can be found in ASTM WK27132, New Practice for Effectiveness of Field-applied Water Repellent Treatments Using a Water Uptake Tube, by ASTM Committee D01.47 on Concrete, Stone, and Masonry Treatments. (back to top)
4 See the Roel Hendrickx article, “Using the Karsten Tube to Estimate Water Transport Parameters of Porous Building Materials,” published in the 2012 Materials and Structures Journal (Springer Netherlands). (back to top)
5 See “Non-Destructive Determination of the Penetration Depth of Impregnation Materials” by Gerd Pleyers and H. Rainer Sasse, as part of ASTM STP 1355-1999, The Use of and Need for Preservation Standards in Architectural Conservation. (back to top)
6 See “Measurement Techniques” by E. De Witte, et al., which appeared in Evaluation of the Performance of Surface Treatments for the Conservation of Historic Brick Masonry Research (report No. 7, published in 1996 by the European Commission). (back to top)
7 See “Consolidants Lab Tests, Evaluating Performance & Durability” by Alice Custance-Baker of the Scottish Lime Center Trust (scottishlimecentre.blogspot.com). (back to top)
8 See “Comparison of Non-destructive Techniques for Analysis of the Water-absorbing Behavior of Stone” by Delphine Vandevoorde, et al., delivered at the 12th International Congress on the Deterioration and Conservation of Stone (2012). (back to top)
9 See “Test Methods for the Evaluation of the In-situ Performance of Water Repellent Treatments” by Rob. P. J. van Hees, et al. (Delft University of Technology, 1995). (back to top)

Adrian Gerard Saldanha is completing his master’s degree in construction engineering and project management at the University of Texas at Austin (UT). He is a graduate research assistant in The Durability Lab—a testing center at UT established by Building Diagnostics Inc.—to study the durability of building components, identifying factors causing premature failure. He can be contacted at asaldanha@buildingdx.com.

Doris Eichburg is a principal with Building Diagnostics Inc., specializing in the investigation of problems with existing buildings, designing remedies for those problems, and resolving disputes that arise from them. She also participates in the company’s research group, The Durability Lab. Eichburg can be reached by e-mail at deichburg@buildingdx.com.