Our technical representatives often provide on-site project support to our customers. This is especially crucial when problems arise. Our job is to diagnose and provide solutions to get our customers back to business as usual. This is the second of a four story series of troubleshooting and prevention blog posts.
Outgassing on a Suspended Slab
The Scenario: This job called for an acid stained concrete slab with a Poly 250 sealer coat. The first coat of Poly 250 was put down and cured with a lot of bubbles in the coating. The contractor applied a second coat of Poly 250 and the same thing happened.
From the looks of the bubbles, it appeared the concrete slab either had a tremendous amount of outgassing or the product had been applied too thickly. Two sample tests were suggested to help control the outgassing:
∑ Option 1: Scuff the coating using a black janitorial pad under a floor machine, and then apply up to four coats of wax.
∑ Option 2: Sand the coating using a sand screen and then apply a third coat of Poly 250 to encapsulate or fill the open capillaries in the concrete that were causing the outgassing.
The contractor decided to go with the first option. This did help control the bubbles, yet in areas where larger crater-like bumps were formed, the wax was too thick and dried white in color.
Why Did This Happen:
An APF technical representative was sent on site for further inspection. He first noticed the concrete was a suspended slab (pan deck). Concrete used for suspended slabs always has a higher water-to-cement ratio to make it more liquid so that itís easier to pump. Concrete with high water-to-cement ratios are most likely to cure out with significantly larger and more abundant capillaries than traditional concrete slabs. These types of slabs end up being more porous, which in turn, increases the occurrence of outgassing.
The Fix: It was suggested the wax be stripped off and the coating removed of all bubbles and craters. Once this was completed, another coat of Poly 250 was applied. Although they were almost certain to get some level of bubbling, another coat would help to encapsulate or fill in the open pores. This next time around, the coating cured out with some outgassing, but it wasnít near the original amount.
For more troubleshooting and prevention tips read more troubleshooting case studies:
Story #1: Epoxy Freeze
Story #3: Job Protection
Story #4: Fixed Up