Road salt
Does road salt hurt a coated floor?
On bare concrete road salt soaks in, and on a coated floor it sits on top of the film, so what is left behind is residue to clean up rather than damage.
The short version
- Salt melt runs off a vehicle as brine, and brine soaks into bare concrete and freezes there.
- On a coated floor the brine sits on the film instead of going into the slab.
- The white haze after a thaw is salt residue on the surface, not a failed coating.
- Water and a mop take the residue off. That is the whole job.
- Where salt still reaches concrete is anywhere the film is open: an unsealed edge, a joint, or a crack.
What road salt does to bare concrete
Concrete is porous. Salt melt comes off a vehicle as brine, the brine soaks into the top of a slab, and it stays there. When it freezes it expands, and it does that inside the concrete rather than on top of it. Enough winters of that and the surface comes apart in flakes and shallow pits, which is the spalling you see on an old garage apron.
That is the damage a coated floor gets bought to get out in front of. A homeowner in the southwest Twin Cities metro watches a slab go from smooth to pitted over a run of salty winters, and putting a film between the concrete and the road is the reason half of these floors get done at all.
What changes once there is a film on it
A coating is a continuous film sitting on ground concrete. Salt that comes off the vehicle lands on the coating and stays on it, so the brine is not soaking into the slab underneath and freezing in there. It dries into a white haze and it looks worse than it is. The haze is residue on a surface, and it comes up with water and a mop.
So salt on a coated floor is a cleaning job rather than a concrete job. That is what the film is designed to do: hold the brine on the outside where you can get at it. What it does not do is change the slab underneath. That is still concrete, and it is still porous anywhere the film does not reach.
Where salt still reaches the slab
Anywhere the film is open. An edge that was never sealed at a wall or a door opening, a control joint, a crack that has opened since the floor went down, or a chip where something heavy landed. Brine gets into those, runs under the coating and works on the concrete out of sight.
That is why the edges and the joints are the first thing anybody looks at when a coated floor starts to lift near a door. It is also why a chip is worth mentioning while it is small. A repair on the top of the film is a small job. Concrete that has been taking brine under a coating season after season is a larger one.