Replacing a garage floor means demolition, hauling and a new concrete pour. This Old House puts a full replacement at around $12 per square foot, which works out to $4,800 to $6,000 for a typical two-car garage and $2,400 to $3,000 for a single. Tearing out the old slab accounts for $3 to $8 per square foot of that on its own, before any new concrete goes down. The more useful question is whether you need it at all. In most St. Louis garages the answer is no.
The short answer
| What your floor looks like | What it usually needs |
|---|---|
| Hairline cracks, stains, tire marks, a dull surface | Repair and coat |
| Pitting, spalling, a flaking top layer | Grind, patch and coat |
| Cracks that are active, widening or stepped | Assessment first, replacement sometimes |
| A slab that is sinking or badly out of level | Concrete work, which we do not do |
Coating an existing slab runs $6 to $10 per square foot installed and most garages take two to three days. Full replacement is a different trade on a different budget. More detail on epoxy garage floor installation.
Age does not decide this. Condition does.
A 30-year-old garage slab in good shape takes a coating just as well as a newer one. The year the house was built tells you almost nothing about whether the floor needs replacing.
The floor above is stained, blotchy and dull. None of that is structural. It grinds and coats like any other slab.
Which cracks matter, and which do not
Minor hairline cracks are routine and expected in most garage slabs. On their own they are not a reason to replace anything.
What needs real attention is a crack that is active, widening, or stepped, meaning one side now sits higher than the other. A stepped crack points at movement underneath the slab, and movement is the one thing a new surface cannot fix.
The straight lines running across the floor above are control joints. Those are cut on purpose so the slab cracks where you want it to instead of wherever it likes. They are not damage.
Spalling, pitting and low spots
Spalling is the top layer of the concrete peeling or crumbling away. It comes from the freeze and thaw cycle a St. Louis winter puts a slab through: water soaks into the pores, freezes, expands, and pushes the surface apart. Pitting is the same process on a smaller scale. Both are surface problems and both grind out.
Low spots are a different thing. Water that pools in the same place after every rain usually points at drainage or the grade of the slab rather than a worn floor. Coating a low spot leaves you with a coated low spot.
When replacement really is the answer
Replacement is the answer when the slab has lost its base or its structure. A floor that is sinking, one with stepped cracks that keep moving, or one where whole sections have broken up is past repair.
We do not pour concrete. Garage Designs remodels garages and coats floors, so if your slab genuinely needs replacing we will say so and you will need a concrete contractor for that part of it. There is no version of this where we sell you a coating over a slab that cannot hold one.
One more case: if the concrete is brand new, it needs roughly 28 days to cure before it will take a coating at all.
What the work costs, and what is in it
Three packages, all installed, all carrying a limited lifetime written warranty:
- Good, $6 per square foot. Diamond grinding, crack repair, Floorguard HyperBond base coat, full flake broadcast, one Aspartic 85 polyaspartic topcoat.
- Better, $8 per square foot. Adds a moisture barrier.
- Best, $10 per square foot. Adds a second topcoat.
Crack repair is in all three. It is not an add-on you get talked into on the day.
Why coating over an unrepaired crack fails
A crack that is not dealt with will almost always telegraph through a new coating. It usually reappears at the surface within a year or two, because the movement that caused it was never resolved.
Done properly, the crack gets routed out and filled with a flexible repair compound. Then the whole slab is diamond ground, which opens the pores of the concrete so the coating keys into it mechanically instead of sitting on top. Older concrete normally also carries old sealers or contamination that has to come off first, and the slab gets moisture tested before anything is applied.
That prep is the reason a professionally installed floor rarely cracks and a hardware store kit often does inside the first year. The kit skips all of it.
What this looked like in Des Peres
That is the original concrete in both photos. Nothing was torn out. The slab was ground and coated with a non-slip flake system, 800 square feet of it, and the job was done in two days. See the full Des Peres project.
Common questions
Watch Brandon answer these
Short clips from our own installations. Each one plays in a window on this page, so you keep your place. The link under each one opens the full written answer.
Can you install flooring over cracked concrete?
Read the full answer
Can garage flooring be repaired if damaged?
Read the full answer
Can you epoxy over old concrete?
Read the full answer
Do epoxy floors crack?
Read the full answer
What to do next
Call 314-308-7780 or ask for a free in-home estimate. We look at the slab, tell you straight whether it needs repair or replacement, and give you the price and the install dates before anything starts. Fenton, 772 Merus Ct., Monday through Friday, 8 AM to 5 PM. Garage Designs has been remodeling St. Louis garages since 2002.
