Pitted floors
Can a pitted or flaking concrete floor be coated?
A pitted or flaking floor can usually be coated once the loose material comes off and the low areas are rebuilt.
The short version
- Spalling is the top of the slab flaking off. A pop out is a shallow cone where aggregate near the surface froze and pushed.
- The loose material is ground off first. Anything that is going to release is better off releasing under the machine.
- Low areas are filled and brought level before the coating goes on. A coating follows the floor, it does not level it.
- A flake finish hides repaired areas. A solid color shows every one of them.
- A slab losing its surface across most of the floor is a concrete question rather than a coating one.
Why a floor pits and flakes
Spalling is the top layer of the slab coming off in flakes and sheets, usually starting at an edge, a joint, or wherever water sits. A pop out is smaller and rounder, a shallow cone where a piece of aggregate near the surface froze and pushed the concrete off the top of it. Both leave you standing on a floor that is sound underneath and loose on top.
Water gets into the top of the slab and freezes, and it takes up more room frozen than it did as water, so it pushes the surface apart from the inside. Through a the southwest Twin Cities metro winter that happens over and over. A vehicle carrying snow and road salt in keeps the surface wet longer, which is why the worst of it usually sits where the tires park and just inside the door.
Getting a pitted floor ready
The loose material has to come off before anything goes on. Grinding takes the flaked surface down to concrete that is actually attached, and whatever was going to let go is better off letting go under the machine than under a finished floor. What is left is a slab with low areas in it, and those get filled and brought level with a patching material meant to be coated.
Then it gets coated like any other floor. A flake finish is forgiving on a slab that has been through this, because the texture breaks up the map of where the repairs are. A solid color shows every patch, so a floor with a lot of history usually points toward flake.
When it becomes a concrete question
There is a point where the answer changes. If the surface is coming off across most of the floor, if there are areas that break loose under a hammer, if steel is showing, or if the damage goes deep rather than wide, this stops being a coating decision. Patching that much of a slab means the finished floor is sitting on repair material more than on concrete.
That is worth hearing before you buy rather than after. A floor that far gone is a concrete conversation: replacing the slab, or an overlay poured over it, and then a coating on top of whichever one you chose. It is the more expensive answer and it is sometimes the right one, and it is a call somebody has to make standing on the floor.