ISSUE 2/2000 ■ VOLUME 18 ■ NUMBER 2

Journal of architectural technology published by Hoffmann Architects, specialists in the rehabilitation of building exteriors. J Waterproofing Solutions 1 Coatings: Friend or Foe?

John J. Hoffmann, FAIA and Bruce R. Soden

hen it comes to waterproofing, there left unattended, water can penetrate Ware no pat answers. A leaky building can to underlying reinforcing steel, leading be especially frustrating in light of the to structural damage and even more myriad remedial options available, ranging costly repairs. from complete materials replacement, to So is there ever a right time to coat? If repair of components, to sheet mem- coatings can do so much damage by branes, to coatings. When water infiltration locking moisture inside a wall, why are leaves spalled masonry and concrete, they used so extensively? The solution rusted reinforcing steel, and stained lies in using a discriminating sensibility. interior finishes in its wake, the initial With some knowledge on your side reaction is to stop the leak as quickly and an expert opinion to guide you, and with as little disruption as possible. the choice of where and when to coat So what’s an owner, manager, or building need not leave you feeling waterlogged. professional to do? Follow the simple guidelines outlined Gut instinct might be to coat over an below, and you’ll be well on your way offending crack in order to block more to a shipshape structure. water from entering the structure. While this thinking is perfectly logical, more Steps to Waterproofing Success in the often than not it doesn’t help the problem. Use of Coatings In fact, using a coating in the wrong 1. Find the underlying problem. situation, or using the wrong coating for a given material, can actually exacerbate When spalled brick, deteriorating the damage. mortar joints, or delaminating concrete slabs rear their ugly heads, it’s easy to While coatings do block water from mistakenly see the symptom as the penetrating a material, they can also have cause. Patch the unsightly brick and the reverse effect: stopping moisture you’re done, right? Unfortunately, that’s already inside from escaping. No matter not usually the answer. Hoffmann how many precautions are taken to fight Architects is often called on to resolve ➤ A worker spray-applies a breathable water entry, small amounts of moisture repeat repairs that have failed time and elastomeric coating to a concrete inevitably find their way in. The more time again. These clients, understandably, corporate facility. waterproof the coating, then, the harder throw up their hands after several it becomes for that trapped moisture to unsuccessful repair efforts and ask us: escape. Eventually, moisture may build up what do we do with this mess? behind the coating and erode underlying brick, stone, or concrete. If the problem is (continued on page 2)

John J. Hoffmann, FAIA, Principal of Hoffmann Architects, is a nationally recognized expert on building envelope rehabilitation. As Senior Project Manager, Bruce R. Soden oversees a variety of waterproofing projects for the firm. JOURNAL

(continued from page 1) The first step is a thorough investiga- culprits, adding a water repellent coating tion into the likely sites of water will do little to address the problem. In infiltration. Case in point: limestone fact, change in the absorption properties may be deteriorating due to moisture of masonry or concrete may have no infiltration at cracked mortar joints. effect on the water penetration of the A waterproof coating applied once wall system as a whole. failed to help, so it was reapplied two Water infiltration is one of the most or three more times over a period of frequently encountered problems with a few years. But delamination only exterior walls, and its effects can be seemed to get worse. The problem? ➤ When the water repellent coating applied to devastating to the structure. When Water repellent coatings work by this exterior brick wall trapped moisture inside, water passes through the face material, changing the capillary action of the holes were drilled in an unsuccessful attempt to soluble salts may be liberated as pores in the face stone from positive let water back out. moisture turns to water vapor. Ordi- (suction) to negative (repellency). narily, these salts may be deposited on Test probes, laboratory analysis, and site masonry surfaces as efflorescence. In the visits may all be necessary to develop a presence of a water repellent coating, design that will hold up to the abuses of however, they may become trapped weather and aging. Application of a water beneath the surface. As salts crystallize, repellent coating in lieu of necessary they expand, eventually leading to cracks repairs is never a good solution. and spalls in masonry as it tries to In a new structure, it’s important to think accommodate the increase in volume. ahead to where problems could occur in These openings in turn create further the future. Trouble spots such as joints, sites for water entry, perpetuating the flashing, and material intersections should cycle of deterioration. Corrosion of ➤ Applying roofing mastic as a coating on be closely examined. Although water metal reinforcement, ties, studs, and this masonry parapet had little damage- repellent coatings are often prescribed other structural members is also of control success, even as a temporary fix. as insurance against water infiltration, paramount concern with a water Re-building would have ended decay from they cannot compensate for quality infiltration problem. Wood elements the start – and spared the expense of design and construction. Good water- are subject to rotting, mold, and mildew repairing the wall twice. proofing takes into account upkeep growth, as well as moisture-related costs, accessibility by maintenance crews, swelling and shrinkage. Finally, and In the percentage strengths normally life-span and durability, material compat- sometimes most noticeably, water used (5-8%), water repellents will not ibility, and water entry points. Using a penetration can leak through the bridge nor fill hairline cracks and weather-ready facade design can better building envelope to damage interior poorly filled joints in the face of stone minimize water infiltration repairs down finishes. or masonry walls. What’s worse, the road than can provisionary applica- In new construction, the potential for reapplications can reduce the tion of water repellent coatings. accelerated deterioration often out- permeability of the coating, resulting in weighs any benefit of water repellent greater retention of trapped moisture. 2. Consider reasons for use. coatings. Rather than keep moisture That explains the increase in rate of Water repellency. out of the structure and protect against deterioration following repeat In climates subject to freeze-thaw the aforementioned water infiltration application of the coating. conditions, water repellent coatings can problems, these coatings in many cases Other possible sources of water be useful for walls particularly vulnerable serve to lock water into the structure. infiltration include old or weathered to water infiltration, including barrier Instead, quality design and workmanship materials, poor original design or walls and parapets. Where remedial are the best assurance against future construction, and improper installation. waterproofing is called for, application of moisture damage. By looking beyond the outward coatings should be considered only after On an existing structure with water symptoms of the problem, the other repair measures fail to remedy the infiltration problems, several months architect can develop a better, long- problem. If defective mortar joints, should be allowed following remedial term solution to waterproofing issues. copings, sills, or expansion joints are the work to determine if coatings are

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necessary. If the problem persists, or if excess moisture penetration. Less water accelerate carbonation by drying out budgetary constraints preclude a long- absorption may mean decreased the concrete enough to allow more term solution, coatings may be consid- incidence of staining or efflorescence. rapid entry of carbon dioxide. As ered. In the end, however, proper However, if the wall is already stained at always, consult a design professional investigation and repair work tend to be the time of coating application, the dirt for specific coating guidelines, as each the more economically sound decision, and salts may be nearly impossible to building has its individual needs. despite their initially higher investment. remove. Adding a coating only serves When the cost of maintenance is in such cases to seal stains beneath the considered, in addition to potentially clear surface layer. more costly repairs if the coating fails, the Of particular concern with concrete better financial choice, generally, is proper is a natural phenomenon called repair. Again, coatings are not a replace- carbonation. Again, moisture penetra- ment for thorough remedial work. tion is the culprit, but this time it’s Aesthetics. partnered with atmospheric carbon dioxide. As the two enter the concrete One effect of certain coatings is a glossy,

pores, high pH calcium hydroxide is ➤ Even if masonry cracks are patched slick appearance which often darkens the converted to calcium carbonate, which prior to coating application, the problem material, giving it a ‘wet look.’ For some has a more neutral pH. Without an can recur unless the source of deterioration situations, this may actually be an undes- alkaline environment, the protective is also addressed. ired result of poor coating selection or passive oxide layer on underlying steel application. Careful consideration must be reinforcement is destabilized, and the 3. If a coating is needed, select the made of coating properties and compat- metal begins to corrode. As it rusts, appropriate one for the job. ibility with the substrate prior to making a steel expands to several times its selection. Some coatings cause a yellowing normal size, leading to spalls and cracks If after careful evaluation by an ex- of certain materials, or an added sheen. in the concrete, as well as to a general perienced professional, it is deter- Unless these are desirable characteristics weakening of structural elements. mined that your structure would for a given project, alternative options benefit from application of a coating, must be sought. In the case of pigmented Anti-carbonation coatings are often used selection of the right one for the job coatings, color matching is an additional effectively to block the penetration of becomes the next important hurdle. hurdle. To be certain that a coating will carbon dioxide into concrete structures. First and foremost to consider are the have the desired appearance, a test area In order to allow moisture to escape, the function and material properties of the of approximately 4’ x 4’ that includes all coating should be breathable. Keep in substrate. Sub-grade surfaces, for textures and colors to be coated should mind that not all water-repellent coatings example, will have significantly different be pretreated and allowed to cure. are anti-carbonation coatings and should considerations than will above grade The design professional and the owner not be used as such. Many do not form ones, especially when it comes to can then determine whether or not an effective carbon dioxide barrier. Use maintenance in retrofit or repair the material meets the intended of an inappropriate coating may actually applications. Below grade waterproof- aesthetic goals. ing is usually applied negative side, or Another consideration for many public on the side of the wall opposite water buildings is resistance to graffiti. Some contact, whereas above grade water-repellent coatings have the added waterproofing is most often applied benefit of keeping graffiti and other dirt positive side (see Glossary). Horizontal on the surface of the masonry in order or vertical orientation is another factor to facilitate cleaning. to be considered. Whereas high gloss may be desirable on some exterior Protection of substrate. walls, the necessary coefficient of

On masonry with a relatively high ➤ Two good reasons to use coatings: improved friction for traffic surfaces (usually 0.5) absorption, such as that which has been water repellency and ease of graffiti removal. precludes use of such slippery sandblasted, colorless coatings are Moss growing in joints is evidence of excessive coatings. Finally, different materials sometimes used to protect the wall from moisture in the wall. respond in different ways to a

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(continued from page 3) given coating, so what works on 4. Use proper application technique. concrete may not necessarily work on Even if the right coating is selected for brick masonry. Barrier walls without the a given project, problems can still result waterproofing protection of interior air if application is not executed correctly. space and weep holes may also have Certain coating deterioration issues different coating responsiveness than such as delamination, cracking, and does a cavity wall system. blistering may be avoidable if care is Selection Criteria taken in surface preparation and Factors to consider when selecting a coating technique. coating vary depending upon the goals Before any coating is applied, surface Although coatings can make a facade of the building owner and design team, defects must be corrected in order appear neat and uniform, that may be as well as on the unique properties of to create a uniform area for coating merely a superficial integrity. the structure. When comparing what can application. Any dirt, dust, grease,

➤ (top) This wall stayed dry only to the be a daunting array of coating options, efflorescence, curing compounds, paint, depth of coating penetration – just a however, it does help to keep in mind or other foreign matter should be fraction of an inch. The rest of the brick the following criteria in order to narrow cleaned, and surrounding areas protected absorbed water, which remained trapped the search: from overspray or accidental incorrect behind the coating. Notice, too, the sheen • Aesthetics brushwork. Atmospheric dirt will interfere of the coated surface.

➤ with proper penetration or adhesion of (bottom) Although this masonry seemed • Water penetration and water repellency the coating. To clean concrete or masonry, to be in perfect condition, partial removal • Breathability procedures such as ‘power washing’ are of the face brick revealed inner wythes that • Durability and life-span often used, wherein high-pressure water had crumbled nearly to dust. • Maintenance/upkeep requirements or steam, sometimes mixed with mild detergents, forces dirt off an exterior • Environmental issues surface. Other methods include hand- • Material compatibility scrubbing, air blast cleaning, and simple • Economics vacuum or broom cleaning (for horizontal surfaces). On historic structures and soft • Desired effect (e.g. carbonation masonry, long-term soaking and washing resistance, graffiti prevention) loosens hardened grime without hurting The accompanying chart lists several delicate materials. Sandblasting or harsh of the more significant properties for chemical washes are not recommended, various coating types and coating as they tend to cause more problems by alternatives (e.g. liquid membranes). damaging the substrate than they solve For a particular application, some coating by removing stains. properties may play a more important role than others in the selection process. It is crucial to wait a minimum of 24 In a concrete building designed to hours following any kind of water washing prevent the spread of fire, addition of a before applying a coating, in order to coating with low fire safety ratings would allow the wall to dry sufficiently. Cleaned negate the structure’s inherent flame surfaces should be tested for moisture at retardance. A sub-grade garage in an various sites just prior to application. If enclosed space precludes use of certain excess hydration remains, the coating will coatings due to their high VOC content trap it inside the wall, exacerbating any (see Glossary), as fumes could be water-related deterioration problems. hazardous to workers or tenants. Cracked or otherwise damaged materials Always remember to check material should be repaired or replaced; coating data sheets for specific coating proper- over a crack will not prevent moisture ties, as values may differ significantly infiltration. Freshly repointed mortar or from product to product. sealant joints should be allowed to cure

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TYPICAL VALUES FOR SAMPLE COATING TYPES PRODUCT Silane/ Liquid TYPES Elastomeric Non-elastomeric Polyurethane Cementitious Siloxane Membranes PROPERTIES Acrylic Acrylic (Penetrating) (Protected) Water Vapor high moderate low high high low Transmission (Breathability)

Elongation moderate low very high does not elongate does not elongate moderate (Crack-bridging)

Tensile Strength low moderate/high high low/moderate does not develop low tensile strength

Adhesion low moderate high varies penetrant; moderate/ not on surface high

Carbonation high not generally no data not generally penetrant; no data Retardance effective effective not on surface

UV Resistance high moderate varies high penetrant; not exposed not on surface

Accelerated Weathering excellent, no excellent moderate, moderate/high penetrant; not exposed cracking or chalking slight chalking not on surface

Fungus and moderate moderate/high high moderate moderate not exposed Mildew Resistance

Wind-Driven Rain no passage no passage no passage no passage no passage not exposed

Flame Spread none none varies none none not exposed

VOC Content low low varies low high varies

Used For concrete; masonry; concrete; pools; concrete; stone; concealed stucco masonry; balconies; masonry; brick; applications stucco concrete stucco concrete

Note: Be sure to check material data sheets for each item under consideration, because individual products vary widely in their properties, even within a given category. The above table is not intended to be a complete listing of the product types available, but rather a comparison of some of the many coating options on the market in terms of properties and applications.

GLOSSARY with a variety of tests, both in the Positive side waterproofing: Waterproof laboratory and in the field. barrier on the side of applied hydrostatic Water vapor transmission pressure (water is blocked from entering (breathability): Rate and amount of Carbonation: In concrete, the reduction in alkalinity that occurs when atmospheric substrate). Typical applications include above- water which can evaporate through the ground surfaces and below-grade structures. coating on the exposed face of a surface. carbon dioxide reacts with moisture. Can lead to corrosion of reinforcing steel Negative side waterproofing: Water- Elongation: Measure of a material's ability to in concrete. stretch, such as bridging a crack formation. proof barrier on the side opposite to Volatile organic compounds (VOCs): applied hydrostatic pressure (water is Tensile strength: Resistance of a material Materials containing carbon, hydrogen, and permitted to enter substrate). Typical to longitudinal stress. oxygen characterized by low vapor pres- applications include below-grade surfaces Adhesion: Tenacity with which the coating sure at ambient air temperature. Often where positive-side, exterior application bonds to the substrate. Can be measured hazardous if inhaled in significant quantity. is not possible. HA

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stress. Field tests of adhesion and water repellency are useful guides, as are laboratory tests like that of accelerated weathering. Bear in mind that these are not firm indicators of a coating’s actual life-span, however, as building conditions and site location also play important roles in coating durability. Coatings in areas subjected to heavy foot traffic and weather conditions, for example, would break down much more readily than those applied to a vertical surface shielded from wind-driven rain. Certain coatings are also highly susceptible to UV radiation, and degrade more rapidly

➤ When coupled with proper investigation and repair, coatings can be successfully integrated into than others in areas receiving a high a waterproofing project. Not only does this coating improve the water repellency and carbon- level of direct sunlight. Greater depth of ation retardance of these concrete columns, it enhances their appearance as well. Note the use penetration or film thickness also implies of cloth coverings to prevent overspray from accidentally damaging surrounding surfaces. increased durability, along with resistance to environmental stressors. at least 72 hours before a coating is mended coverage, two or more applica- When selecting a coating, be sure to applied, again to ensure that no excess tions may be necessary. Occasionally, use one from a well-known manufac- water is locked into the structure. In different techniques must be used for turer with a good track record. If weather conditions such as extreme subsequent coats, so consult the product possible, investigate references of heat or cold, wind, or rain, the area application guidelines for details. projects with similar scope and condi- must be protected and coatings should tions in which the product was used not be applied. Avoid coating in direct 5. Promote coating life-span. successfully. Don’t be afraid to request heat of sun, as this may result in too Even the most scrupulous surface test reports of performance criteria rapid drying of the material and cause preparation and application technique such as water repellency, VOC emissions, bubbles or wrinkling. Be sure to check cannot correct for an improperly and water vapor transmission, as well as the specific temperature range selected coating, or for using a coating a written warranty from the coating recommended by the manufacturer, where repairs would have been manufacturer. When it comes time to as these vary from product to product. more appropriate. Likewise, extensive apply the coating, verify qualifications Keep in mind that checking the research into materials compatibility and of the contractor and be certain that ambient temperature may not be product selection is no match for sloppy they have ample experience in the sufficient; surface temperatures may application. For a coating to last its full work to be performed. A design be significantly hotter or colder. anticipated life-span, careful selection, professional should be on hand for Different coatings require different preparation, and application procedures construction management to ensure application methods, but common must all be in order, coupled with good that coating application is performed practices involve use of a brush, roller, maintenance practice. as specified in the documents. or spray, moving in one direction. Always apply a coating according to the 6. Keep up maintenance work. Working in smaller areas helps to manufacturer’s instructions to ensure full Once the decision is made to apply reduce the incidence of ‘lap marks,’ warranty benefits in case the coating a coating, it is extremely difficult or, which are color, sheen, or texture should fail earlier than promised. often, impossible to return to an variations where one freshly coated Hoffmann Architects often prescribes uncoated surface. In coating a structure, area overlaps another. Thorough mixing more stringent field requirements in you create a long-term maintenance of the coating, along with proper order to extend the life of the coating. dilution according to the manufacturer’s issue, one which must be taken into instructions, will contribute to a uniform Advance testing can be a good way to account in the initial budgeting of final appearance. To obtain the recom- determine a coating’s durability under water infiltration solutions.

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Waterproofing Hoffmann Architects understands the frustration a less-than-watertight structure can cause. As specialists in the rehabilitation of building exteriors, we have extensive experience in water infiltration diagnosis and repair, which enables us to rectify waterproofing problems as efficiently and with as little disruption as possible. Working with clients to meet budget and design goals, ➤ Pu’u Po’a Condominiums Princeville, Kauai, Hawaii (Pu’u Po’a Association of Apartment Owners) we develop a custom waterproofing program for each project. Among Hoffmann Architects’ water- Buckingham Condominiums Long-term solutions begin with a proofing projects are the following: Stamford, thorough investigation into the cause Alderman Library (Buckingham Condominium Association) of water entry. Once the team locates Charlottesville, Virginia Taft High School problem areas, design options are (Hartman-Cox Architects for University , New York considered, and the owner and of Virginia) (New York City School architect work together to select the G.E. Corporate Headquarters Construction Authority) best remedial strategy. To ensure Fairfield, Connecticut 605 Third Avenue quality workmanship, Hoffmann (General Electric Corporation) New York, New York Architects oversees implementation (605 Third Avenue LLC) of the design—from blueprint to 55 Messerole Street Plaza Downstate Medical Center balustrade. When the new system is New York, New York Parking Garage in place, the project team develops a (EMTEC Consultants, Inc. for Bell Atlantic) Brooklyn, New York program of maintenance that will keep Chase Manhattan Centre (New York State University the structure free from leaks for years Wilmington, Delaware Construction Fund) to come. (Bassett Partners) Funger Hall, Ross Hall, Stockton Hall Washington, District of Columbia (The George Washington University) 1211 Avenue of the Americas Plaza New York, New York (TechSource Services, Inc. for Management Corporation) Xerox Document University Leesburg, Virginia (Xerox Corporation) HA

➤ Prudential Eastern Operations Office Dresher, Pennsylvania (The Prudentatial Insurance Company of America)

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JOURNAL is a publication of Hoffmann Architects, specialists in the rehabilitation of building exteriors. The firm’s work includes investigative and rehabilitative architecture/engineering services for the analysis

➤ To determine if a coating will be appropriate for a given application, field tests can be used to and resolution of problems within measure effectiveness. Here, an adhesion test (left) and a thickness reading (right) are conducted roofs, facades, glazing, and structural on sample areas of coating. systems of existing buildings, plazas/ terraces, and parking garages. (continued from page 6) Please send news, technical information, Any additional maintenance work Most coatings must be reapplied address changes, or requests for free every seven to fifteen years, and many stipulated for the manufacturer’s warranty subscriptions to Editor, Hoffmann require much more frequent or recommended by the design profes- Architects JOURNAL, 432 Washington application, on the order of one to sional would also need to factor into the Avenue, North Haven, Connecticut three years. Future maintenance long-term budget. When considering the 06473. For answers to specific questions issues may be problematic when an expense of recoating and upkeep, using or for information on the services existing coating is incompatible with a coatings as cheap, quick-fix solutions Hoffmann Architects offers, please contact newly introduced material. For becomes less attractive as an economic Sandra Matheny at example, a penetrating sealer may alternative. Only when coupled with (203) 239-6660. prevent proper mortar adhesion thorough investigation and repair 432 Washington Avenue when re-pointing or may require methodology do they become a viable North Haven CT 06473-1309 special primers for re-caulking. In part of a sound waterproofing design. 203 239-6660 some cases, reapplication of the 500 Fifth Avenue, Suite 830 coating is difficult, because the Conclusion New York NY 10110-0899 hydrophobic nature of the coating As a building owner, facility manager, or 212 789-9915 prevents adhesion of the new layer. It designer, you want to solve and prevent 1001 Connecticut Avenue NW may then be necessary to strip off water infiltration problems in the most Washington DC 20036-5525 the existing coating before a new efficient, cost-effective manner possible. 202 530-1100 application. However, the hazardous While it’s tempting to reach for one of For more information on the chemicals often needed for this the many products available, coat over topics discussed in this article, procedure may be restricted or a leaking wall, and be done with it, this visit us on the web at prohibited by environmental regula- approach can lead to some complicated www.hoffmannarchitects.com, tions. Such coatings would then need maintenance issues, as well as to even or contact us at to wear off naturally before a fresh greater deterioration down the road. By [email protected]. coat could be added, even if water following the advice outlined in this issue, Editor: Alison B. Hoffmann infiltration problems called for more you can establish a realistic, economically Graphic Services: M&M Design immediate reapplication. feasible plan of attack. HA

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