What is Outgassing and How Is It Prevented

Concrete is one of the most commonly used building materials in the world.  And, what  appears to be a dense solid mass is actually a structure that is very porous with varying sized voids. As such, when temperatures increase, the air inside these voids or pores expand resulting in a phenomenon called “outgassing.” Outgassing itself is not a problem until protective coatings are being applied.  If coatings are applied to an outgassing substrate, pinholes can result, which if not repaired, may substantially reduce the service life of the coating system.  

For that reason, as a coatings applicator, it is important to plan your project to avoid an outgassing substrate as follows:

• Wait to coat surfaces until temperatures are stable or descending.  When the volume of air inside the concrete substrate is stable or contracting.
• Utilize epoxy modified cementitious resurfacers (Tnemec Series 218) to parge the surface and fill voids and bugholes which can contribute to outgassing and pinholes.
• Shade concrete surfaces from direct sunlight.
• Spray and backroll a compatible primer under the right conditions to seal the surface and create a thin film air block.
• If in confined spaces, supply indirect fired heat for a time before coatings will be applied to increase the substrate temperature and turn heat off an hour or two before coating operations resulting in a decreasing surface temperature.

For more information on outgassing, or to discuss coating systems and resurfacers that can help eliminate or remediate outgassing, reach out to High Performance Coatings for more information.