This past Thursday night I put the first coat of finish on the floor of my current build. The house is built on a shallow frost-protected foundation, commonly referred to as a slab. The slab serves as foundation, heat sink for the infloor heat, and finished floor.

I’m aware of two basic ways to top coat a slab. The first happens within hours of the pour. Once the concrete is screeded level a powdered dye is scattered on the surface. This is then worked in by the power trowel. A power trowel looks like a circular floor buff machine on steroids. Four or more rotating blades in a cage about three feet across. If your finish is reliant on a power trowel, getting it done prior to walls going up makes sense. It’s big and can’t get into corners. I’ve only seen this technique used once. After the slab was dyed and worked to a high sheen, plastic was placed on top. The plastic was to trap the moisture of the curing slab, which slows the cure. A slow cure makes for harder concrete. In this case it also transformed a uniformly dyed slab into one with mottled hues. An unexpected and quite beautiful outcome. A winner of a mistake.

My preference is to coat the slab as a final project. I find it much easier not having to worry about building a house on top of the finished floor. I still have the slab power troweled post pour, but not to a high gloss. I also make sure the finished slab isn’t treated with a sealer. A slab finished to high gloss or sealed won't accept a topcoat. If you find yourself wanting to coat a sealed or glassy slab you’ll need to give it some tooth to accept a finish. You can do this with a muriatic acid wash. You’ll need to flood the surface with a dilute acid solution, then wash it off thoroughly. Not a realistic option in a finished house. What I consider the better option is to abrade the surface with an orbital sander. Once water dripped on the surface is absorbed rather than beads, you’re good to go.

Floor preparation prior to applying topcoat, once you’re confident the surface will accept the finish, is similar to any other topcoat prep. Be diligent about cleaning the surface. Vacuum and mop. You can use floor paint or stain. Floor paint affords the option of satin or gloss finish. Remember that a gloss finish will be slick. Not a great choice for a bathroom. Stain will be flat. Cut in your edges with a brush, roll the field. My smaller houses take about three hours to coat the entire first floor. You’ll need two coats. Putting the finish down will dramatically alter the interior look. It’s a lot of visual bang for a three-hour task.