Here is an example of how to fix cracked floor tile on a concrete slab foundation. This post gives a quick explanation for why ceramic or porcelain floor tiles crack, how to match and replace the tile floor tiles, how to re-grout so the repair isn’t obvious, and how to ensure that they won’t just crack again.
Why do floor tiles spontaneously crack?
Ceramic, porcelain, and natural stone tile is very hard but brittle. So, if you drop something hard on a tile floor then you’re probably going to crack or chip a tile.
But floor tiles can also crack seemingly all by themselves when the substrate that they’re bonded to shifts or flexes. Tiles can’t shift or flex in response. When stressed, brittle tile cracks. If you have cracked floor tile, then the specific explanation for why depends on the substrate.
If the cracked tile was laid over a plywood subfloor, then:
1) The plywood subfloor is too bouncy for a normal tile install, because it was built using below-code floor joists or has had past water damage
2) The tile was installed directly on top of previous flooring (usually a layer of old laminate) that is shifting underneath the tile
If the cracked tile was laid over a concrete subfloor, then
1) The concrete slab foundation has itself shifted and cracked
2) The concrete slab foundation is in a location that experiences significant heat gain variations (like an outside patio or open sunroom), and the resulting expansion and contraction placed too much stress on the tile
What’s the most common cause?
When folks call me with cracked floor tile problems, it’s almost always because the tile is on a concrete foundation slab that has shifted and itself cracked.
Hearing the phrase “cracked foundation” usually really freaks out homeowners. It conjures images of their home being swallowed by underground caverns, which is something that actually does (rarely, but sometimes) happen around Austin.
Fortunately, concrete slabs also shift a bit (and sometimes crack a bit too) as just part of the settling process that happens in the first few years after a home is newly built. As a concrete foundation slab cures (a process that is mostly complete within 28 days but still continues for years after a slab is poured), the concrete literally shrinks as trapped water molecules either evaporate out or continue to be slowly incorporated into the crystal structure of the concrete aggregate.
So, a few cracks in a concrete foundation slab isn’t necessarily a fearsome harbinger of doom. If your home has just a few cracked tiles and no other symptoms of foundation problems (cracked drywall, stuck door jambs, etc), then it’s almost certainly not a real big deal.
Even if your home has a floor tile crack that runs all the way across a room, it’s still probably not a big deal if the surface crack doesn’t widen over time. If, on the other hand, you have a floor tile crack that’s getting wider along with widening cracks in the drywall and doors that are starting to stick ‘cuz they’re getting cockeyed … well, then you’ve got a serious problem.
Thankfully, major structural foundation slab slippage is pretty rare even around the Austin, TX, area. Almost all of the concrete slab problem cracks that I’ve come across have been of the relatively benign shrinkage variety:
So, what’s the fix?
Well, the answer to that is a definitive … “it depends.”
For cracked floor tile on a plywood subfloor, a permanent fix depends on what the root cause is. You might need to remove all of the floor tile to start over compeltely if the tile has cracked because the floor is fundamentally too flexy due to floor joists that are undersized or too widely spaced or because it was installed over an old laminate layer.
There are many different strategies for stiffening a plywood subfloor for a guaranteed crack-free tile flooring install. There are also some basic commonsense solutions. But any true fix for a floor that needs more structural support or a crack prevention membrane won’t be cheap, since the first step is to remove everything to the subfloor.
For cracked floor tile on a concrete slab foundation, a permanent fix usually requires a lot less work and expense. So long as the foundation slab is stable, it’s usually just a matter of chipping out and replacing just the tiles that have cracked due to slab settling.
For extra permanent fix assurance, it’s a good idea to use a quality highly modified thinset for the tile (re)install. Modified thinset mixtures have polymer latex additives that make the concrete thinset mix a bit flexible, which puts a bit of flexibility into the bonding layer between the concrete (or plywood) subfloor and the brittle tile on top. It can absorb some of the stress that would otherwise be translated directly up to the tile layer.
Okay, what does that process look like?
If the surface tile crack is caused by foundation slab settling, then you probably have a pretty long hairline fracture that looks something like this:
The underlying concrete foundation slab crack usually looks something like this after you remove the surface tile and chip away the thinset:
And, prepping for installing new tiles with a quality polymer-modified thinset adhesive looks like this:
Replacing several cracked tiles to repair a room-spanning fracture looks like this before grouting:
And, after re-grouting, this particular repair job looked like this:
So what’s the deal with the grout shade difference?
Here’s the thing about that. Matching tile is generally pretty easy (or at least binary). Either you have some extra matching tiles on hand, or you can find some matching tiles still in stock somewhere. Or … you can’t.
Either way, replacing tile with new tiles that match is either possible or not. Pretty simple and intuitive.
But grout matching is a bit more analog. Even if you know the exact brand and color of grout that was used originally, getting a perfect match can still be tricky because grout changes with age. Oxidation, exposure to cleaning products, literal dirt accumulation, etc all changes the shade of grout colorants over time.
In the case pictured above, there was a big oblong rug that covered the middle of the tiled livingroom. All of the grout lines along the perimeter of the room therefore had a slightly darker color than the grout lines that were protected by the rug.
Here is a closeup view of the shade difference:
There are some additional tricks that you can use to blend the shade differences so that the demarcation line between new and old grout is at least gradual. But in general, replacing and re-grouting just some of the tiles in a floor will result in at least a somewhat noticeable grout shade difference to a very discerning eye.