Tiny holes scattered across a cured epoxy floor, like the surface of a sponge, are pinholes. They come from air escaping the concrete or the mix as the coating sets. They are small, but they trap dirt, weaken the film, and signal a prep or timing problem. Here is what causes them on Katy floors and how we fix them.
What pinholes are
Pinholes are pin-sized voids left when a bubble of air rose through the wet coating and the surface healed around the edge but not the center, leaving a small open hole. They differ from blisters (larger raised bubbles) and fish-eyes (crater-like depressions from contamination). Pinholes are usually many and small, and they are most common over porous or open-pored concrete.
What causes pinholes
Outgassing from the concrete. Porous concrete holds air in its pores. When the slab warms, that air expands and pushes up through the wet epoxy. The most common trigger is coating while the slab temperature is rising, for example in the morning as a Katy garage heats up, so air is actively expanding out of the concrete and through the film.
Air entrained in the mix. Mixing too fast or with the wrong paddle whips air into the resin, and those bubbles surface as the coating self-levels.
Skipping a primer or grout coat. On open, porous concrete a penetrating primer or a grout coat fills the pores first, so the build coat is not fighting outgassing.
Coat on a falling temperature
The professional trick to beat outgassing is timing: coat when the slab temperature is stable or falling, not rising. On a falling temperature, air contracts back into the concrete instead of bubbling out through your floor. We schedule Katy installs around the slab's daily temperature curve for exactly this reason.
How we fix a pinholed floor
The cure depends on severity. A lightly pinholed surface can be abraded and sealed with a thin, low-viscosity coat that fills the holes, followed by the finish coat. A badly pinholed coat is ground off and rebuilt with proper prep: a primer or grout coat to seal the concrete, controlled mixing to limit entrained air, and application timed to a stable or falling slab temperature.
Preventing pinholes
Good prep and timing prevent nearly all pinholing: diamond-grind and assess porosity, prime or grout-coat porous slabs, mix at the correct speed to avoid whipping in air, and apply on a stable or falling temperature. These controls are why professional floors come out smooth and sealed.
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Get a Free QuoteFrequently Asked Questions
What causes pinholes in an epoxy floor?
Pinholes form when air escapes the concrete or the mix through the wet coating. The main causes are outgassing from porous concrete (worst when the slab is warming), air whipped into the resin during mixing, and skipping a primer or grout coat on porous slabs.
Are pinholes a serious problem?
They are small but they trap dirt, weaken the film, and indicate a prep or timing issue. Left alone they can become wear points, so they are worth sealing or recoating.
How do you stop outgassing pinholes?
By priming or grout-coating porous concrete to seal the pores and by applying the coating when the slab temperature is stable or falling, so air contracts into the concrete instead of bubbling out.
Can a pinholed floor be saved without full replacement?
Often yes. A lightly pinholed surface can be abraded and sealed with a low-viscosity coat that fills the holes before the finish coat. Severe cases are ground off and rebuilt with correct prep.