Repairing Bubbles and Craters in Epoxy and Urethane Floors

Bubbles and craters in newly installed concrete floor coatings often come from gases flowing through the porous cement. These gases can be argon, methane, or whatever is under the slab. Sometimes the gases come from chemical reactions still being produced by the preparatory floor cleaning process. Often the gases derive from air being sucked into the room by the heating system or by natural airflow. We describe here a simple, effective solution for repairing these defects.

Many times just screening the floor and putting on another coat will solve the problem, but not always. That is, even after a second coat, there may be telltale signs of bubbling. Look closely at one of the bubbles, remove any skin and see if there is a small hole at the bottom of the crater. This small hole is a sign that something is blowing through the hole, causing the bubble. For a positive cure, use glazing compound to fill each hole before your next coat. While this sounds like a big job, in fact a 1200 sq. ft. floor can be filled by you and a helper in about an hour.

Here are the steps for positive repair and concealment of your cratering problems. First, use a rotary scrubber and drive pad with a 60-grit screen to quickly go over the floor, shaving off any bubble tops and thereby flattening the floor. Next sweep up the screening dust. Then put on those kneepads and, using a tooth paste-style tube of glazing compound and a putty knife, start filling. After all the problem craters are filled, screen again. A good second screening can be done as soon as you are finished filling. This screening will quickly remove excess glaze and blend each hole flat. Sweep again and then coat the floor.

With this extra hour of work you can be sure that the holes are all permanently filled and with no holes remaining in the floor, there should be no new bubbles or craters. Make sure that when you mix your floor coating you don’t whip air into the mixture. I use a hand paddle for about 200 strokes then let the mixture sit for 20 minutes before using it, pot life permitting. If you suspect that your roller cover is pushing air into your product use a mohair-style roller cover, and pour the product on the floor; don’t dip the roller into it. Having the room temperature near 70 degrees and preventing wind and hot or cool spots is also helpful.