Efflorescence on a Stained Floor Slab

By Chris Sullivan – ChemSystems, Inc.

Question:

We have a stained concrete floor slab on grade in our Houston home. We have salts that our escaping and clouding the floor. During the three years we have lived in the house, our builder has tried various things to fix the floor. First, he tried redoing the stain and sealer, but the same discoloration happened. About six months ago, the builder removed the sealer and waxed the floor to allow it to breathe and the salts to rise through the floor. The salts are now easily wiped away, but the wax is wearing off, onto our socks, shoes, the dog's paws, etc. Can anything be done to salvage the floor? We have thought about tiling over it, but are any special preparations necessary, such as applying a thin-set mortar or a moisture barrier?

Answer:

It sounds like you have a chronic efflorescence problem. Efflorescence is a process where salts leach out of the concrete, carried by water, and end up on the surface as a white dusty residue. Since you have had this issue since you've lived in the home, it seems to be chronic and ongoing. Since water is the trigger, do you have a high water table, flood plain, or other situation that's causing water to get under your concrete foundation? Anything you can do to minimize water migration under your concrete will help. This would include installing French drains or possibly regrading the slope of your property.

No matter what you do, the efflorescence problem will need to be mitigated. Efflorescence will not only cause problems with a stained concrete floor, it can also delaminate tile and warp wood floors. The best approach would be to strip all the sealer and wax off the concrete. Once the sealer and wax are removed, a moisture test should be conducted so you can get an idea of how much water is moving through the slab. The test results will dictate your next step. If the water movement is low, a penetrating sealer designed to stop or slow efflorescence can be used. After the sealer is applied, you can reapply a stain or dye to the floor. If the water movement is high, a more drastic and aggressive topical waterproof coating may have to be used. If you then want to restain the floor, a cement and polymer topping would need to applied to create a new canvas on which to apply the stain. If you want to tile over the floor, the same water mitigation procedures would have to be completed.

Chris Sullivan
White efflorescence caused by high water movement pushing salts out of a concrete floor slab.