Spalling is one of the most common problems I see on Wisconsin garage floors, and the good news is most spalled floors can still take a great coating. The bad news is it adds time and money to the job, and any contractor who quotes a spalled floor at the same price as a clean one either isn't looking or isn't planning to fix it right. Here's how I actually repair spalling before a coating goes down.
What is spalling?
Spalling is when the top surface of concrete flakes, chips, pops out, or scales off. You'll see shallow craters, rough patches where the smooth trowel finish used to be, and sometimes larger sections where half an inch of the slab has broken loose. It's almost always caused by one of three things in this climate:
- Freeze-thaw damage. Water gets into the pores of the concrete, freezes, expands, and pops the surface off. Most Wisconsin garages see this every single winter.
- Road salt and deicer. Salt brine tracked in on tires accelerates the freeze-thaw cycle and chemically attacks the cement paste.
- Bad finishing when it was poured. Concrete that was troweled while bleed water was still on top ends up with a weak surface layer that was always going to fail.
If your garage wasn't sealed when it was new and you've been driving salted tires into it for ten winters, you probably have some spalling. It's that common.
Can a spalled floor be coated?
In most cases yes, as long as the spalling is surface damage and not structural damage. Pop-outs and scaling in the top quarter to half inch are repairable. If the slab is fracturing deeper than that, or if chunks of aggregate are loose, we're in the territory I talked about in signs your concrete might be too far gone to coat. For everything short of that, the repair is straightforward.
Step 1: Diamond grind to sound concrete
The first pass of the diamond grinder is doing double duty. It's opening the slab to a CSP 2-3 profile for the coating, and it's knocking off every loose piece of spalled concrete that's still hanging on. Anything that's going to pop later needs to pop now, while I still have the grinder running.
On a spalled floor I grind more aggressively in the damaged areas. The goal is to get down to concrete that rings solid under the machine instead of crumbling. Sometimes that means going an extra pass or two on the scaled sections. When I'm done, the damaged areas are cleaner, deeper divots, but they're sound.
Step 2: Fill with TerraMend polyurea
Now I fill the divots. My repair material is TerraMend 100% solids polyurea. It's the same family as the coating itself, which matters for bond. A polyurea repair under a polyurea coating chemically ties in. A cement patch under a polyurea coating doesn't, and you end up with a patch that telegraphs through the finish or delaminates later.
TerraMend has a few things going for it in a cold climate:
- 100% solids, so it doesn't shrink as it cures
- Cures from -20 degrees to 130 degrees Fahrenheit
- Stays flexible, so it moves with the slab through freeze-thaw cycles
- Grinds and shapes cleanly once it's set
I mix it, trowel it into the repair areas, and overfill slightly so I have material to grind back flush. Small pop-outs get filled with a putty knife. Bigger scaled sections I'll fill in pours and work in lifts if they're deep.
Set time is fast. On most garage repairs I can move on in 15 to 30 minutes.
Step 3: Grind the patches flush
Once TerraMend has set, I go back over the repaired areas with the grinder and bring them flush with the surrounding slab. This is the step that separates a good repair from a bad one. If you just fill and coat, you get a bunch of raised humps that you can feel with your foot and see in the reflection. If you grind flush, the coating goes on perfectly flat and you'd never know the repair was there.
At this point I also re-check the surrounding concrete with the light. Grinding a repair sometimes exposes a little more weak material at the edges. If so, I re-fill and re-grind. It takes as long as it takes.
Step 4: Base coat goes down
After the repairs are flush, the floor gets vacuumed one more time and the Valence base coat goes down. Because TerraMend is from the same polyurea family, the base coat bonds right to the repaired areas just like it bonds to the ground concrete. No primer boundary, no separation.
How much extra does spalling repair cost?
Honest answer: it depends on how much damage there is. A floor with a dozen scattered pop-outs might add an hour and $100 in material, which I often just eat on the quote. A floor with heavy scaling across the whole main drive path might add a half day and several hundred dollars. I price it at the estimate after I look at it, not sight unseen.
For a sense of where baseline pricing starts, check our post on garage floor coating cost in Wisconsin. Spalling repair is on top of that.
What you should not do
I want to name a few shortcuts I see all the time that don't work:
- Skim patching with a bag of concrete patch from the hardware store. The patch doesn't bond to polyurea. Your coating will fail at every patch.
- Coating right over the pop-outs without filling them. The coating bridges the hole for a while and then collapses into it.
- Filling with caulk or asphalt patch. Nothing I need to say here. Just no.
The repair is the reason the coating lasts. Skip the repair and you're building on a cracked foundation.
If your garage is spalling and you want an honest look at whether it can still be coated, I'll come out and walk it with you. See more on our surface prep and repair page, or get a free quote or call Dave at (715) 307-8302.