The Misconceptions of Liquid Applied Waterproof Membranes

This summary was provided by Dave Fuller, an employee of QXO. The full article was originally written by Daniel Aleksov, P.Eng., BSS for the Concrete Repair Bulletin in January 2022 and can be found here: https://lsc-pagepro.mydigitalpublication.com/publication/?i=734574&p=26&view=issueViewer

Construction professionals understand that correctly applying a waterproof membrane where needed can improve project outcomes and extend the life of structures. However, there are several misconceptions about waterproofing membranes—liquid-applied waterproof membranes in particular—that can cloud their understanding of how and where to apply these coatings.

Unfortunately, acting based on incorrect information or assumptions can lead to project failures and have costly ramifications. An article in the Concrete Repair Bulletin does an excellent job of “busting” some of the most common myths about waterproof membranes.

We've summarized it below. If you're a construction industry decision-maker, influencer, or simply someone who wants to be better informed about the work, we encourage you to read on.

Why Misconceptions Occur

Before listing and explaining the top misconceptions about liquid-applied waterproof membranes, the article addresses how the misinformation arises in the first place. Three primary causes are covered:

• Lack of knowledge and experience in this area. Post-secondary institutions typically provide little, if any, education on waterproofing. Professionals often develop their expertise on job sites, and if they are exposed to the wrong information, they may perpetuate it.
• Poor understanding of the pre-application site conditions. Many factors affect waterproofing systems, from the existing substrate and previous coatings or decking systems to temperature, moisture, and other ambient conditions. Sometimes, inaccurate ideas are generated while trying to manage those variables effectively.
• Incorrect assumptions about waterproof membrane systems and what will work. Every project is different and has unique waterproofing needs. A system that worked flawlessly on one project may not be appropriate for the current one. That misalignment can result in mistaken beliefs about processes and applications.

The 10 Most Common Misconceptions About Liquid-Applied Waterproof Membranes

1. Newly placed concrete with a broom/trowel finish does not require surface preparation.

   All surfaces require proper preparation before waterproofing. A rough or patterned finish isn’t enough for the waterproofing material to establish a proper mechanical bond.

   Abrasive blasting or shot blasting and cleaning are recommended.

2. Using handheld grinders is sufficient surface preparation for waterproofing applications.

   In most cases, this approach will not produce the necessary concrete surface profile (CSP 3-4) for applying liquid-applied waterproof membranes. Incorrect usage may result in “polishing” the surface, which can lead to adhesion issues.

3. Using high-early-strength ready-mix concrete means you can apply waterproofing sooner.

   This is a reasonable but incorrect belief. The article points out that it “incorrectly correlates concrete strength as a benchmark for timing of waterproofing membrane application.” More relevant than concrete strength is the moisture content of the substrate when the membrane is applied.

   Practices like using a moisture meter or the plastic sheet method can indicate the presence of moisture and the need for more drying time and/or further testing.

4. Waterproofing can be applied to a non-vented composite deck or hollow core slab.

   Waterproof membrane manufacturers discourage this type of application. It is essential to understand the site conditions and the type of floor slab to determine whether a membrane will adhere properly.

5. Moisture only moves vertically in a slab.

   This is another reasonable—but incorrect—assumption. Gravity does pull fluids downward, but moisture can spread horizontally from walls as well.

   Lateral movement may also occur due to failed vertical coatings and sealants or waterproofing within underground parking garage trench drains.

6. Chloride-contaminated concrete surfaces are acceptable to waterproof.

   If you suspect chloride contamination, testing is crucial since chlorides can attract moisture through osmosis, resulting in premature waterproofing failure.

   Additional preparation measures may be necessary for contaminated surfaces.

7. Thicker polyurethane membrane systems are better.

   Waterproof membrane systems are designed to specific thickness levels and undergo testing to attain the required properties.

   Membranes applied too thick can often bubble, blister, and become susceptible to premature wear. Quality control measures, such as measuring the wet film thickness, are critical during waterproof membrane installation.

8. Thinner (light-duty) polyurethane membrane systems can be applied to the top (roof) decks of multi-story garages.

   The useful service life of a thinner coating will vary significantly based on the amount of vehicle traffic.

   Conducting a thorough site assessment is essential, considering factors such as past waterproofing performance, environmental conditions, wear patterns, and potential long-term damage risks. Often, it may be appropriate to install thinner and thicker systems on the same project due to location and traffic patterns.

9. Crystalline coating is considered a traditional waterproofing system.

   The article debunks this, saying that crystalline coating systems are classified as plugs, meaning they stop the flow of water through cracks or joints from the interior side and are not typically used as a positive-side (exterior) waterproofing system.

   If the positive side is easily reachable, it is important not to use this as a replacement for the existing failed water barrier.

10. The waterproofing will last 20 years without any maintenance.

    This may be wishful thinking. Isolated issues such as early wear, chipping, and peeling are common at penetrations, joints, and high-traffic areas.

    Ignoring these symptoms and failing to perform routine maintenance can result in further deterioration of both the waterproofing system and the underlying structure.

Facts Not Fiction: Tackling Liquid-Applied Waterproof Membrane Projects the Right Way

Calling out misconceptions about waterproof membranes and replacing them with facts is vital to the success of projects and the construction industry. This Concrete Repair Bulletin article does a tremendous job in that regard, and we encourage you to read it.

If you have questions about waterproofing and restoration projects, contact our waterproofing team at your local branch.