How to Reduce Alkalinity on Concrete

Install a sub-slab vapor retarder that's the size of the slab before you pour the concrete. Sub-slab vapor retarders act as a roof beneath the surface of the building. They are often made of low-density polyethylene and are 0.25 mm thick. The vapor retarder protects the building slab from absorbing the moisture in the soil beneath, which increases alkalinity.

Cure the wet concrete for seven days with a curing blanket. During curing, you will want to protect the moisture in the concrete to reduce cracking, dusting and scaling. Curing is not the same as drying concrete and can be done with chemicals. Testing by the Portland Cement Association shows that concrete that has been cured with a blanket is less permeable, meaning it will ultimately resist moisture and increased alkalinity.

Allow time for the concrete to dry fully, regulating the environment if possible. The drying process varies based on the water-to-cement ratio, slab thickness and temperature. During curing and drying, the moisture and alkali will rise to the surface of the concrete slab, leaving a white residue that may disappear on its own. You can spray off the residue with clean water after the concrete is finished drying.