Spec notes · 2026-09-27

Epoxy over an old basement floor: paint, carpet glue, tile, and patches

Very few basements around Cape Girardeau and Jackson are bare concrete by the time someone wants them coated. The slab has usually been several floors already. Gray porch paint from one owner, wall-to-wall carpet from the next, a corner of old square tile nobody wanted to pull up, a patched line where a drain got added. Each of those layers has to be dealt with before a coating goes down, and they come up in roughly the order below.

Can epoxy go over a painted basement floor?

No. Paint is a layer with its own weak bond to the slab, and a coating rolled over it is only as attached as the paint underneath. For basement floor epoxy to hold, the paint comes off in the grind and the coating bonds to sound concrete. If the paint was already flaking, that tells us something about the slab too.

Porch and floor enamel is the usual one in older houses here, often in gray or that brick red, sometimes two or three coats of different colors from different decades. It grinds off. The grinder loads up faster on paint than on bare concrete, so a painted floor takes longer on prep day, but the result is the same open surface.

The part worth paying attention to is where the paint had already failed before anyone touched it. Paint that peels in the same patches every spring is often the first sign of vapor coming up through the slab, and the moisture read on basement slabs covers what that means for a coating. On prep day a peeling paint map mostly tells us where to put the meter.

What happens to carpet glue, pad residue, and the tack strip holes?

The adhesive is ground off with the top of the slab, and the nail holes from the tack strip get filled before priming. Glue matters most. Any that stays in the pores of the concrete keeps the primer from reaching the slab in that spot, and it can surface months later as a soft or lifted patch in an otherwise sound floor.

Carpet in a basement usually leaves three things behind. There is the tack strip itself, nailed around the perimeter a few inches off the wall. There is pad residue, which can be anything from crumbs of foam to a sticky film where a rubber pad broke down against damp concrete. And under a glue-down carpet or an indoor-outdoor product there is adhesive spread across the whole field.

Tack strip comes up with a bar before the grinder starts, and it leaves a line of small holes, sometimes with broken nail shanks still in the concrete. Those get cleared and filled so the perimeter reads flat under the coating. Pad residue mostly comes off in the grind.

Adhesive is the slow one. Some carpet glues soften and smear under a grinder instead of cutting cleanly, and a crew will switch tooling or scrape first to keep from spreading it around. The goal is concrete that looks the same color as the rest of the floor, with no shiny or dark areas where glue soaked in. A coating laid over a glue shadow tends to look fine on the day it is installed. The trouble shows up later, when that patch starts to feel different underfoot or a bubble forms in a spot with no other explanation.

Can a basement floor be coated over old tile?

Not over the tile. It comes up first. Old 9x9 floor tile and the black mastic under it can need testing before anyone breaks or grinds it, and that is a question for a testing lab. If the result says the material needs special handling, removal is a different trade’s job, and the coating waits until they finish.

Square tile shows up in plenty of older basement rec rooms and laundry areas, often in a checkerboard or a speckled beige, with a black or dark brown adhesive underneath. Sometimes the tile is gone and only the black mastic is left, which is the same question in a different form.

Nobody can tell what is in those materials by looking at them, us included. A sample goes to a lab, and the result decides the path. We coat floors. We do not do that kind of removal, and we will not grind tile or mastic that has not been cleared. If the lab clears it, it comes up and the slab gets the same prep as any other floor. If not, the removal happens first, by the trade that handles it, and our work starts on the slab they leave.

Newer vinyl, peel-and-stick squares and click-lock plank are a simpler case. They come up, and whatever adhesive they left behind is treated like carpet glue.

What about a patch, a leveler, or a trench someone already poured?

Patches take a coating differently from the original slab, so each one gets checked. A hammer and the grinder tell whether it is sound. A patch that rings solid and grinds like the surrounding concrete stays and gets bonded into the prep. One that sounds hollow or lifts at the edges gets cut back and redone before any primer goes on.

Most basements have at least one. The common ones here:

• A trench across the floor where plumbing was added for a laundry line, a bathroom, or a sump. The fill is newer concrete, often a different color, sometimes a little high or low at the seams.
• Self-leveler poured by a previous owner to flatten a low corner before carpet or tile went down. Some levelers are hard and well bonded. Others are soft on top, and those grind away faster than the slab around them.
• Hand-troweled fills around posts, old oil tank legs, or where a wall was taken out.

Newer concrete in a trench also needs time to dry. A trench that was poured recently can read wetter than the old slab around it, and it gets its own reading.

If a bathroom or wet bar rough-in is anywhere in the plans for the basement, that plumbing work should happen before the coating, not after. Cutting a finished floor means a patch in it.

The mechanics of grinding and crack filling on an older slab are the same downstairs as in a garage, and they are laid out in why we grind instead of acid etching. If the basement already has a coating that is failing, grinding it off works like any other layer on this list, and repair, recoat, or redo goes into how to tell which one it needs.

How does the coating meet the floor drain and the sump pit?

It follows the floor down to the drain and stops cleanly at the edge of the grate, and it stops at the rim of the sump pit without going into it. The slab pitches toward the drain, and the coating keeps that pitch rather than filling it in. The sump basin and its lid are left alone so the pump can still be pulled and serviced.

Most basement floors slope, sometimes gently and sometimes enough to roll a marble, toward a floor drain near the furnace or water heater. A coating is a thin film. It does not level that slope, and it should not, because the slope is how water finds the drain. The crew grinds right up to the drain body, keeps the grate removable, and finishes the coating at the metal so there is no loose edge for water to get under.

The sump pit is handled the same way at its rim. The pit liner is plastic or concrete, it gets wet by design, and a coating inside it would do nothing useful. What matters is a clean, sealed line where the floor meets the pit opening and a lid that still lifts off.

How is the edge where the floor meets the wall finished?

Two ways. A straight edge stops the coating where the slab meets the wall and leaves the joint as it was. A radiused cove carries the coating a few inches up the wall with a rounded transition, so the joint is sealed and there is no corner for water or dirt to sit in. The cove is an option on any basement floor.

On a straight edge, the baseboard or the bottom of the foundation wall sits over the coating, and the joint between slab and wall stays open underneath. That is fine for a dry room with baseboard trim going back on.

The cove makes more sense where water has ever crossed the floor, whether from a sump that overflowed or a water heater that let go. With a cove, water on the floor stays on the coated surface and can be squeegeed to the drain. Without one, it finds the gap at the wall and sits under the edge of the coating, and under drywall if the room is finished.

A cove also makes a laundry room easier to mop, since there is no corner for mop water to collect in.

What does a basement floor cost once the old floor is off?

On a bare, prepared slab, solid-color basement systems in the Cape Girardeau area run $4.50 to $7 per square foot installed, and metallic finishes run $9 to $14. Taking off paint, carpet glue or tile is priced as prep on the written estimate for that floor. We do not publish a removal price, because two basements the same size can need very different amounts of it.

The difference comes down to what the crew finds. One coat of paint over a sound slab adds some grinding time. A full floor of glue-down carpet adhesive over a leveler that has to come out adds a lot more. The estimate lists each of those lines separately, so you can see what the old floor costs to undo before the new one goes down.

The table behind those numbers shows what a basement floor costs here next to the garage and polyaspartic systems. If the meter calls for a vapor-mitigation primer, that shows up as its own line too.