Most calls here start with a coating question. What a crew looks at first is the concrete.
By the time a garage floor here is eight or ten winters old, the slab has taken a specific set of injuries: flaking at the door, pits in the two lines where the vehicle parks, a crack that was not there when the house was built. Garage floor repair is what happens to those before a coating is discussed at all. Below, how each kind of damage reads and what a crew does about it.
Why is my garage floor flaking and crumbling at the door?
That is spalling, the surface of the concrete breaking away in flakes and scales that leave shallow craters with the aggregate showing through. Water works into the top few millimeters of the slab, freezes, expands, and lifts the paste off in layers. The apron at the garage door takes it first and worst, because that strip catches meltwater off every vehicle all winter and it is the coldest concrete in the building.
The tell is underfoot. Run a boot across the apron and see whether grit comes loose that was not there a second ago. A sound slab does not sand off. A spalling one sheds a little every time something drags across it, and the craters have sharp shoulders where the intact surface ends.
De-icer accelerates it. Chloride keeps the surface damp longer than it would otherwise stay, so the same January night puts a slab through more freeze cycles at the apron than three feet farther in. That is why the damage almost always stops in a rough line a foot or two inside the door.
Why do the tire lanes pit while the rest of the floor looks fine?
Pitting in the parking lanes is chemical rather than structural. Magnesium chloride brine off Highway 95 and the interstate rides in on the undercarriage, drips into two lines under the vehicle, and stays wet under there long after the open floor has dried. Chloride goes after the cement paste at the surface, and the paste is what gives up.
What you see is a field of small pits, most of them under a dime, concentrated exactly where the wheels sit and nowhere else. Sweep the lane in April and a fine sand comes up with the dust. That sand is the slab.
None of it is deep. It is a surface condition, and the surface is what a coating has to bond to. The pits get filled and the weakened paste gets ground away, or the primer soaks into a layer already on its way off the floor.
Which cracks get filled, and which ones mean something bigger?
A stable crack gets cut open, filled and ground flush, and it disappears under the coating. A crack that is still moving does not disappear, and no crew should promise it will. The difference is whether the two sides have shifted relative to each other: lay a straightedge across it or run a palm over it and feel for a lip.
Three things a crew is sorting for:
- A hairline shrinkage crack, wandering, no displacement, usually showing up in the first year of the slab’s life and dormant since. Chase it and fill it.
- A control joint, which is a saw cut the finisher put in on purpose to tell the slab where to crack. It is not damage, and it is honored rather than glued shut, because filling it rigid moves the crack somewhere you did not choose.
- A crack with a lip you can feel, or one running out of a corner that has settled. That slab has a movement problem, and a coating on top will telegraph it within a year. Worth knowing before you spend on a floor, not after.
The repair on the first kind is a crack saw down the line to open a clean kerf, a vacuum, then a fill. A semi-rigid polyurea is the usual product because it stays slightly flexible and takes the grinder without smearing. Rebuilding a spall is a different product entirely, and the two get confused constantly.
What are the cone-shaped pop-outs in a newer slab?
A pop-out is a small cone of surface concrete that has lifted off, and there is usually a piece of aggregate sitting at the bottom of the hole. A soft or porous stone sitting close under the surface takes water on, freezes, expands, and pushes the paste above it off. Newer slabs out on the Rathdrum Prairie show them more than older floors in town do.
They are not a sign the slab is bad. Local pit-run aggregate carries the occasional stone that does not belong that close to the surface, and when it lets go it takes a thumbnail of concrete with it. They keep appearing for a few winters, and a coating laid over them maps every one, because the film follows the shape it is poured onto.
They get filled during the patch pass with the same mortar the spalls get. On a floor with dozens of them, the fill pass is most of the repair day.
What order does a garage floor repair happen in?
Repairs happen after the grind, not before it. The slab gets diamond ground first so the crew is looking at real concrete instead of a dusty surface, and a fair amount of suspect material comes off with that pass. Then the damage gets addressed in order, and the whole floor is brought back to one plane before any primer is mixed.
- Diamond grind with dust extraction, edges hand-detailed, so the true extent of the spalling shows. Craters are always bigger than they looked.
- Cracks cut open, vacuumed and filled, then shaved flush.
- Spalls and pop-outs rebuilt with a polymer-modified repair mortar, feathered past the crater edge so there is no shelf to catch a squeegee.
- Patches ground level with the surrounding slab once they have set.
- A moisture reading on the repaired floor, then primer.
That sequence is the front half of the install described on the garage floor coating page, and it is the half nobody photographs. On a written estimate it shows as its own line, crack and spall repair, priced before the work starts rather than discovered on the day, and on most garages in this county it runs $150 - $600.
When is garage floor resurfacing the answer instead of patching?
When the damage covers most of the floor rather than sitting in a handful of spots. Garage floor resurfacing means putting a new wearing surface across the whole slab, typically a polymer-modified overlay poured and troweled over the prepared concrete and then coated as though it were new. It earns its cost once the surface has scaled across most of the floor, or once the patches would add up to more area than the sound concrete left between them.
It is the wrong answer in three situations. On a slab that is moving, an overlay cracks where the slab cracks and you have paid for a second surface to break. On a slab still giving off moisture, the overlay and the coating both fail together. And on a floor with four spalls and a crack, an overlay is several times the price of the repair that would have done the job.
One expectation is worth setting before the repair day. Patched concrete under a solid color still reads as patched concrete, because a single flat film shows every change in texture underneath it. Under a full broadcast of flake it does not. If the floor is going in as flake, the patches have to be solid, and they do not have to be pretty.
What happens if a coating goes over unrepaired spall?
It fails inside one winter, and what lets go is the concrete under the coating. A coating bonds to whatever it touches. When what it touches is a loose, brine-soaked, half-detached surface layer, the coating grabs that layer and the layer lets go of the slab beneath it. The edge at the apron lifts by the second thaw, usually in one piece with concrete stuck to the back of it.
That is the failure to look for when a bid comes in far under the others. The grinding is visible in a quote and the repair line often is not, and a floor quoted with no repair on a slab that plainly needs it is a floor quoted to be redone. The redo costs more than the original, because it now includes grinding a failed coating off before the repair that should have happened the first time.
Does the repair have to happen before the ground freezes?
The repair itself can be done cold. Leaving the damage open through winter is the expensive choice. Every unfilled spall and every open crack holds water, and a Kootenai County winter runs a slab through freeze and thaw dozens of times between November and March. The crater the size of a hand in September is wider in April, and it has taken the concrete around it along.
The coating is the part with a calendar. Epoxy wants the slab in the fifties, which an unheated garage here does not offer past October, so plenty of floors end up repaired in the fall and coated in the spring, or finished in a cold-curing system instead. Either way the concrete work is the piece that should not sit through another winter open.
So go out this week with a flashlight held low to the floor. Raking light throws shadows into pits that overhead light hides completely. Run a hand across the apron and see what comes off on it, look at both tire lanes, lay a straightedge over any crack and feel for a lip. Then count how much of the floor is actually damaged, because that is the number that decides the estimate. Four craters and a dormant crack is a repair line. Damage wherever the flashlight points is a resurfacing conversation, and September is a cheaper month to learn that than April.