Liquid-applied below-grade waterproofing: Best practices for working with STPE

by Samantha Ashenhurst | July 11, 2018 9:28 am

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by Curt Liscum
Waterproofing is the art and science of minimizing the potential for water ingress into a structure by treating surfaces to resist the passage of water under hydrostatic pressure. While it sounds similar, waterproofing is different from dampproofing, which is defined as treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.

The pressure exerted by water at equilibrium at a given depth due to the force of gravity is known as hydrostatic pressure. This is important in below-grade applications because it increases in proportion to depth below the surface due to the increasing weight of the water exerting downward force from above. Fresh water exerts a pressure of about 3 kPa (0.43 psi) per foot of water, so a 3-m (10-ft) foundation wall with a 1.2-m (4-ft) groundwater table would exert a pressure of about 14 kPa (2 psi) at the base of the foundation wall. Without a waterproofing treatment on such a foundation wall, the pressure will ultimately force water into the structure, causing damage in the process.

“Positive-side” waterproofing refers to the application of a waterproofing membrane on the side of the wall in direct contact with the water and hydrostatic pressure—generally the exterior side of a wall. Positive-side waterproofing seeks to prevent the water from entering into the wall, protecting the structural element from corrosive chemicals in groundwater as well as freeze-thaw cycle damage. This stands in contrast to “negative-side” waterproofing, which refers to the application of a waterproofing material to the wall side opposite of the water contact or hydrostatic pressure—generally the interior side of the wall. Negative-side waterproofing allows the water to enter into the wall but minimizes its impact to the building occupancy. The main benefit of negative-side waterproofing is it can be installed without having to excavate and expose the exterior of the foundation wall or structure, and it is thus often applied as a repair to failed positive-side waterproofing measures.

Positive-side waterproofing can take several forms, including sheet-applied modified bitumen (mod-bit) and single-ply membranes, liquid-applied materials (both reinforced and non-reinforced), bentonite clay products, and hybrid systems. Each material and system has its advantages and specific application parameters. This article focuses on liquid-applied systems that offer several advantages including:

• monolithic construction;
• self-terminating nature;
• limited fastener corrosion;
• ease of application;
• no open flames or kettle requirements; and
• flexible material delivery.

Benefits of an STPE-based liquid product
A good example of liquid-applied waterproofing is a single-component, moisture-cured silyl-terminated polyether (STPE) elastomeric material. STPE is a hybrid product comprising silicone and polyurethane technologies. Combining these chemistries brings together the most desirable features of each and creates a durable, high-quality product. STPE technology is engineered to not only produce strong performance in end-use applications, but also to be safe for workers and the environment. Other common names for this chemistry include MS polymer, silyl-modified polyurethanes (SPUR), polyether, silyl-terminated polymer (STP), and silicone-modified polyester (SMP).

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STPE-based products contain extremely low levels of volatile organic compounds (VOCs), offer excellent cure times, and perform well at temperatures as low as 1.6 C (35 F). STPE technology is suitable for projects requiring flexibility in design, as these products typically do not require primers, offer a broad adhesion profile for many types of projects, and are compatible with a wide range of substrates.

Single-component products are also beneficial to the installer as they can be used directly from the pail with minimal initial mixing. Most single-component products must be mixed for uniformity and consistency, but catalysts, accelerators, hardeners, or other components need not be added. A high-solids, single-component, moisture-cured STPE elastomeric, liquid-applied waterproofing material is also advantageous as the amount of material applied to the surface is close to the finished membrane thickness. The higher the percentage of solids within a material, the lower the volatile content, and therefore, there will be little shrinkage in film thickness as solvent evaporates during the curing process. For instance, using a 98 percent solids material (the recommended minimum) and targeting a 2.2-mm (90-mil) wet film thickness (WFT) application rate, the cured finished membrane would be about 2-mm (88-mil) dry film thickness (DFT) of material.

Unlike other solvent-cured, adhesive-adhered, self-adhered, or heat-welded products, a liquid-applied STPE product will not blister, outgas, or lose adhesion when installed over damp or fresh “green” concrete surfaces due to STPE’s moisture-curing nature. Once the wall obtains sufficient strength for form removal, and the initial concrete set is achieved (generally within two to seven days), the waterproofing material can be applied. This can significantly accelerate the construction schedule.

Cure time will vary from minutes to hours depending on applied film thickness, temperature, and relative humidity (RH). Typical cure time is three hours for 0.7-mm (30-mil) applications at 21 C (70 F) and 50 percent RH, but this may be extended in cooler, drier climates. In ultra-dry climates, additional water misting may help accelerate curing. Full, normal curing is anticipated in three to four days, and supplemental coats and repairs should be performed within 72 hours of the initial application.

Single-component, moisture-cured STPE elastomeric, liquid-applied waterproofing material is manufactured in several viscosities (or thicknesses) depending on application method. The lower the viscosity—measured in centipoise (cP)—the easier it is to deform, or in this case, apply. One advantage of a well-formulated, single-component, moisture-cured STPE elastomeric, liquid-applied waterproofing material is it has the necessary viscosity to be spray applied. This can create labor savings for contractors installing below-grade waterproofing.

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How to work with STPE-based products
It is important to contact manufacturers for product- and application-specific requirements, recommendations, and precautions. Nevertheless, below is a general overview of the steps to follow in working with a single-component, moisture-cured STPE elastomeric, liquid-applied waterproofing material.

Surface preparation
Always begin with proper surface preparation. Once the concrete forms are removed and the wall or structure is determined to be safe and self-supporting, substrate preparation can begin. The surface must be cleaned of all contaminants that can interfere with bonding. Even though this is a moisture-cured product, surfaces must be dry to the touch and free of obvious moisture before product application begins.

Adhesion testing
Perform adhesion testing on all substrates, especially with applications over existing or in-situ materials. Adhesion peel tests are typically performed in accordance with ASTM C794, Standard Test Method for Adhesion-in-Peel of Elastomeric Joint Sealants. Adequate resistance to peel adhesion is normally demonstrated by cohesive failure, where most of the waterproofing material remains on the substrate. Any failure should be evaluated to determine suitability and the degree of surface preparation needed. One must not use asphalt-based primers as they deter adhesion of most STPE-based materials.

Transition detailing
Once the substrate preparation is complete, transition detailing can ensue. Installers should pay special attention to corners, cracks, and other areas requiring extra application of the STPE-based liquid product along with polyester reinforcement. Apply flashing-grade, STPE elastomeric, liquid-applied waterproofing material to create a smooth surface for membrane application anywhere voids exist. Wall penetrations, such as pipes, should also be flashed using normal roofing/waterproofing flashing procedures with reinforcement and STPE liquid material.

Field membrane installation
Once the surface preparatory and detail work are complete, field membrane installation can begin. The material can be installed reinforced or non-reinforced. Although the STPE elastomeric, liquid-applied waterproofing material can be installed with a brush or roller, the fastest and most economical application method is spray application. With any liquid-applied membrane it is important the finished material be installed in a continuous, uniform application of the appropriate thickness free of voids and pinholes. On rough, porous substrates, additional material will be required to achieve the desired thickness and consistency.

Protection course
Once the STPE elastomeric, liquid-applied waterproofing material is cured, a protection course can be installed. The protection course can be any moisture-resistant substantial material with the ability to provide adequate protection to the waterproofing membrane. After installation of the protection course, a drainage panel could be installed to allow for free movement of the groundwater to a drainage tile or other water-removal provision. One must be careful when backfilling to protect the waterproofing components already in place.

Tips for installation success
The installation of a positive-side, single-component, moisture-cured STPE elastomeric, liquid-applied waterproofing material can provide a very cost-effective, functional system for a building or structure. As with any field-installed material, however, specific installation prompts are warranted and can make all the difference to the longevity of the material.

Consistency
It is important to maintain a uniform consistency of the product throughout application. This is accomplished by initial and periodic mixing when using drums or totes.

Product temperature
The product should be stored and maintained above room temperature, 20 to 22 C (68 to 72 F) before application. This may take several hours when employing drums or totes.

Substrate temperature
The product should not be installed when ambient or surface temperatures are below 1.6 C (35 F). Although the ambient temperature may be above the 1.6 C limit, the cold mass of concrete may be well below this acceptable parameter.

Substrate preparation
The substrate should be free of all dirt, oil, loose paint, water, frost, form-release agent residue, lime, and other contaminants that can interfere with bonding.

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Detailing
Cold joints, cracks, inside and outside corners, footing/wall intersections, penetrations, concrete spalls, holidays, honeycombs, and voids must be detailed and reinforced as necessary.

Product adhesion
Membrane adhesion can generally be improved by the application of a “kiss” or primer coat of material to the substrate.

Uniform continuous coverage
The spray gun should be perpendicular to the substrate with overlap spray patterns. Application using “cross patterns” helps to ensure uniform, full coverage with minimal pinholes.

Membrane thickness
All coating thicknesses should be verified using a wet-film mil gauge.

Intercoat delamination
In multicoat applications and with repairs, one must apply additional coats as soon as the first coat is firm but within 72 hours of the initial application.

Reinforcement
Penetration, transition, and detailing reinforcement should be fully embedded and coated with material. In no case should dry reinforcement touch each other.

Reinforcement wrinkles
Consider employing flashing-grade material to embed and hold the reinforcement prior to installing the topcoat.

Protection-board placement
The protection course should be adhered to the membrane and never be mechanically attached to the wall.

Penetration damage
Prior to installing the protection board, flashing grade fillets should be installed around all penetrations to prevent lateral movement of the protection course that could damage the penetration flashing.

Drainage panels
The drainage panel should be constructed and installed in such a manner to prevent plugging the drainage channels with backfill material.

Backfill damage
The backfilling operation should be accomplished with care to protect the waterproofing components in place.

While a variety of product and application methods are available for a positive-side, below-grade waterproofing job, a single-component, moisture-cured STPE elastomeric, liquid-applied system—especially one which is spray-applied—is an economical method of restricting the ingress of hydrostatic water pressure for waterproofing a building or structure. In addition to ease of application, the moisture-cured attribute allows for an accelerated application schedule, thereby reducing the overall waterproofing schedule.

Curt Liscum is the technical services manager for Soprema USA and is responsible for field technical, warranty evaluations, and warranty claims. Liscum has worked in the roof/waterproofing consulting industry for more than 30 years, performing design, evaluation, construction management, and forensic analysis services. He can be reached at cliscum@soprema.us[5].

Source URL: https://www.constructionspecifier.com/liquid-applied-below-grade-waterproofing-best-practices-for-working-with-stpe/

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