The presence of pinholes in liquid-applied waterproofing products is a problem faced by all of us at some time. When this occurs on exposed external surfaces it can result in water ingress and damage.
When concrete surfaces are ground it exposes the pores of the substrate. These pores can trap moisture and gases within the concrete especially when newly laid. Changes in temperature, pressure or even sunlight can cause gases to escape from the substrate in a process called off-gassing. When waterproofing is applied over a surface that is still off-gassing, tiny bubbles form in the liquid membrane as the gases escape, leading to pinholes in the membrane. These pinholes compromise the waterproofing, allowing moisture ingress. This is why it is so crucial for your primer coat to fill every single pore so as to block the passage of these gases and to ensure that your membrane has no weak spots.
The purpose of the primer is to seal the pores of the substrate and to ensure maximum adhesion of the waterproofing membrane and no pinholes.
If the concrete/substrate is still curing or contains moisture, the moisture will rise to the surface and push its way through the waterproofing membrane causing pinholes and delamination. It is thus essential to ensure that the surface is fully dry before applying the waterproofing. The use of a moisture meter to determine the levels of moisture in the substrate is strongly advised.
High humidity or rapid temperature changes during application of many liquid-applied membranes, especially polyurethanes, can cause premature curing, trapping air or moisture in the membrane. This appears as bubbles in the product, ultimately leading to
pinholes. Regular checking of weather forecasts is a major factor in project management. Some products will specifically advise against application if rain is expected within a few hours.
Applying product too thickly can result in the surface drying faster than the layer beneath. This creates trapped air pockets that eventually lead to pinholes as the product cures unevenly. Application of multiple thinner coats will prevent these problems.
Like the application of any product, surface preparation is key to a successful outcome. Taketime to inspect your substrate prior to application and take all necessary steps and precautions to avoid possible failure. Doing it right first time will prevent the need for costly remedial work and damage to your professional image.
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