Pinholing is a defect where tiny pinprick-sized holes form in a curing coating, most often caused by air or moisture vapor escaping from the concrete substrate through the wet film.
Understanding Pinholing in Epoxy and Polyaspartic Floors
Pinholing is a defect where tiny, pinprick-sized holes form in a coating as it cures. Unlike fisheyes, which are caused by contamination sitting on the surface, pinholes are usually caused by something escaping from underneath the coating, such as trapped air or moisture vapor pushing up through the slab.
What Causes Pinholing?
Porous concrete that has not been properly sealed or primed can trap air in its surface pores, which releases as tiny bubbles while the coating cures and leaves pinholes behind. Moisture vapor moving up through a slab that has not been tested or treated is another common cause, especially on new concrete that has not fully dried. Applying a coating too thick or during rising temperatures can also pull air out of the film as it cures.
Pinholing vs. Outgassing
Outgassing is the broader process of air or gas escaping from the concrete into a wet coating, and pinholing is one of the visible results of that outgassing. Not all outgassing leads to pinholes, especially if it happens early enough in the cure for the coating to self-heal, but heavy outgassing late in the cure almost always leaves pinholes behind.
Practical Tips for Preventing Pinholes
Properly profile and prime porous concrete before coating so trapped air has an escape route before the topcoat goes down. Test the slab for moisture before starting the job, especially on newer concrete, and address any issues before coating. Avoid coating during rising temperatures when possible, since a slab that is heating up pushes more air out through the surface.
Also Called
Pinholes, off-gassing pinholes
