Solving Pinholes and Adhesion Issues in Your Waterproofing Membrane

Are you constantly dealing with pinholes in your waterproofing membrane or noticing that adhesion is failing? You’re not alone—these are some of the most common problems in the industry, especially in exposed external wet areas.

At The Waterproofing Shop, we inspect waterproofing work on a daily basis and have identified key causes behind these issues. In the photos attached, you’ll notice significant pinholing in a moisture-cured/solvent-based polyurethane membrane. Additionally, the membrane has peeled off the substrate—clear signs that the surface preparation was not done correctly.
After further inspection, we discovered several key reasons behind pinholes and adhesion failures:

1. Improper Cleaning After Grinding

After the concrete roof was ground, the surface needed thorough cleaning using a high-pressure washer or industrial vacuum. This step was skipped. Often, dust and debris left behind after grinding aren't visible to the naked eye, and blowing the surface isn’t enough. The dust sticks in the small pores created by grinding, affecting adhesion.

2. Concrete Off-Gassing After Grinding

When concrete surfaces are ground, it exposes the pores of the material. These pores can trap moisture and gases within the concrete. Once opened up, the gases begin to escape in a process called off-gassing.
Changes in temperature, pressure, or sunlight can trigger the gases to expand and rise to the surface. When a waterproofing membrane is applied over a surface that is still off-gassing, tiny bubbles form as the gases escape, leading to pinholes in the membrane. These pinholes compromise the waterproofing, allowing moisture to penetrate the surface.

That’s why it's crucial to ensure that the primer coats fill every single pore to block these gases before applying the waterproofing membrane.

3. Incorrect or Insufficient Primer Application

Applying a primer incorrectly or using insufficient coats can result in incomplete sealing of the concrete's pores. For optimal adhesion, the primer should fully penetrate the substrate. To prevent pinholes:

• Apply 2-3 coats of epoxy primer:
• The 1st coat should be mixed with 20% water to ensure deep penetration into the concrete’s pores.
• The 2nd coat should be mixed with 10% water to fill remaining gaps.
• An optional 3rd coat with no water can ensure full pore coverage.

4. Moisture in the Substrate

If the concrete is still curing or contains residual moisture, that moisture can evaporate and push its way through the waterproofing membrane, creating pinholes. It's essential to ensure the substrate is dry before applying the membrane. A moisture meter should be used to confirm that the substrate meets the required dryness levels.

5. Application in Humid or Unfavorable Conditions

High humidity or rapid temperature changes during membrane application can cause premature curing, trapping air or moisture in the membrane. These factors can also cause bubbles to form, leading to pinholes. Always check the environmental conditions before applying a waterproofing membrane to ensure they are within the recommended range.

6. Excessive Film Thickness

Applying the waterproofing membrane too thickly in a single coat can result in surface curing faster than the layers underneath. This creates trapped air pockets that eventually form pinholes as the membrane cures unevenly. Applying the membrane in multiple thin coats helps avoid this issue.

Conclusion

To avoid pinholing and adhesion failures:

• After grinding, always clean the surface thoroughly using a high-pressure washer or industrial vacuum to remove all debris.
• Apply 2-3 coats of epoxy primer with appropriate water dilution to ensure full pore coverage.
• Ensure the substrate is dry and environmental conditions are favorable during application.
• Avoid applying the membrane too thickly in a single coat.

By taking these steps, you can effectively prevent pinholes, enhance adhesion, and ensure long-lasting waterproofing performance.

Feel free to reach out if you need advice or further clarification on preventing pinholes and ensuring perfect adhesion on your next waterproofing job.