Basement Floor Epoxy in St. Louis, MO

Basement floor epoxy is one of the most useful upgrades in a St. Louis home, and one of the easiest to get wrong. Basements here often have bare or painted concrete floors that shed dust, stain easily and feel damp. A basement floor coating seals that concrete, brightens the room and makes it easy to clean. But a basement slab sits in the ground, and moisture moving up through it is the most common reason basement coatings fail. That is why testing comes first on each basement we take on.

Old slabs, no vapor barrier

ACS figures summarized by Point2Homes show more than half of the homes in the city of St. Louis were built in 1939 or earlier. In Affton the median home dates to 1958, in Florissant to 1963 and in Mehlville to 1969. A basement floor from those decades may have been poured without a plastic vapor barrier underneath. Moisture vapor can move up through the slab year round. You may not see it, but trapped under a coating it can build pressure and push the coating off in blisters. Newer basements in O'Fallon and Wentzville get the same test, because age alone does not tell us what a slab is doing.

The ground under the house

The St. Louis area sits on limestone and dolomite bedrock, and Wikipedia notes karst ground with sinkholes and caves south of downtown. Missouri's state soil, Menfro, is a deep silt loam formed in loess near the Missouri and Mississippi rivers. Soils and drainage vary a lot from lot to lot, and so does how wet a basement is. Some homes near the Meramec, the Missouri River or the River des Peres sit on lower ground that has flooded in the past. That is why we test your slab rather than guessing from the neighborhood.

Moisture testing explained

We test basement slabs before we quote a system. Depending on the floor, that can include a surface moisture meter survey, a plastic sheet test that shows whether moisture collects under a covering, or calcium chloride or in-slab relative humidity tests that measure vapor over time. We also look for white mineral deposits, peeling paint, musty smells and staining along the walls, which all point to moisture. The results decide the primer and the system, and sometimes whether a coating makes sense at all.

Choosing the right basement system

When moisture readings are low, a standard 100% solids epoxy base works well, finished with either a flake broadcast or a solid color under a clear topcoat. When readings are higher, we use a moisture-tolerant epoxy primer designed to block vapor before the decorative coats go on. In finished basements, many homeowners choose metallic epoxy or a solid color for a clean look. In laundry and utility areas, a flake floor hides lint and spills. Around the floor drain we slope and finish the coating so water still flows to it.

Humidity during the install

Basements in St. Louis summers stay cool while the air above them is humid. Wikipedia lists the city's average July dew point at 66.6 F and average relative humidity at 69.7%. A cool slab under humid air can collect condensation, which ruins a coating as it cures. We read the slab temperature, air temperature, humidity and dew point before each coat. Running a dehumidifier a few days before the install often helps, and we will tell you if we need it.

When a coating is not the answer

If water comes in as liquid, through cracks, at the wall joint or up through the floor drain during heavy rain, a coating will not stop it. St. Louis averages about 41.7 inches of precipitation a year, and spring storms can test any basement. In those cases the drainage, grading, sump or crack repair needs to come first. We tell you that plainly at the estimate. Once the water is handled, the floor can be tested again and coated. Get a free estimate