Cracked floor tile due to improper substrate preparationI know there are some people out there (not my regular readers like you!) that read what I write and think to themselves ‘okay, but I’m sure that won’t happen with my installation’. So periodically I’m gonna post things like this that show exactly what happens when things aren’t built correctly. And yes, it will happen to yours, too, if the proper steps aren’t taken. If you care to see more train wrecks you can check out my ‘flawed‘ page wherein I post photos of absolutely horrible tile installations which I’ve torn out and replaced.

See that crack in the tile right there? (The line down the center is not a grout line – it’s a crack. You can click on it for a larger version) That bathroom floor is less than eight months old. It was installed with hardibacker over the subfloor and thinset. At least that part is correct, but that was about it. There was no thinset beneath the hardi and the seams between the sheets were not taped and thinsetted. To a lesser extent the correct screws were not used in the hardi – they committed the cardinal sin of using drywall screws in the backerboard. Yeah. Wrong.

So, back to the crack. (Never thought I’d ever type that!) As soon as I walked in and saw it I knew exactly what was wrong and I knew why. The crack was in an absolutely straight line – a dead giveaway that the crack is likely over a seam in the backerboard which wasn’t taped. If you read my post about how to correctly install flooring backerboards you will see that there needs to be thinset below the boards, the seams need to be taped, and the proper screws need to be used. None of which was done.

And here’s what was beneath it: Improperly prepared substrate beneath cracked floor tile

If you click on that photo (I dare you!) you can see the crack follows the seam of the backerboard exactly. Without the tape on the seams the individual boards may move in different directions and, without the support beneath from thinset, they will move independently and eventually crack your tile or, more commonly, your grout lines first.

When you tape and thinset your backerboard seams it will lock the two separate sheets together and any movements in the substrate (seasonal micro-movements, completely normal) will all move as one and in the same direction. This won’t cause any stress on your tile.

I simply pulled up all those cracked pieces and chipped the old thinset out of there, installed proper screws along the seam, taped and mudded the seam (when I say ‘mudded’ the seams I mean thinset) and reset new tiles and grouted it up. Once that grout cures it will lighten and it will look brand new.

Repaired floor tileSo all these little things like ‘tape and mud your backerboard seams’ that I throw out there may seem like it’s just overkill or taking extra precautions which aren’t really necessary – well, they are necessary. And this is why. This will also happen on a shower wall if your seams are not taped and mudded. If the boards move differently it causes uneven stress on your tile – it needs to release somewhere. Ninety seconds worth of work to tape the seam to begin with would have prevented this – just do it! (damnit)

If preventing cracked tile isn’t enough motivation for you maybe this will: all of my regular readers know what happens if your tile or grout crack – your dog will burst into flames! So if you don’t do it for your tile, do it for your pooch. Not only are flaming dogs bad for, well, the dogs, but they tend to run around and catch other stuff on fire too! You don’t want that, do you?

TAPE YOUR SEAMS! :D

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  • Steve

    Hi Jeff,
    I’m a musician, but in these hard times I’m trying to help my parents who got screwed (pun intended?) by a Contractor, so I’m trying to help them finish, first project is tiling a pretty simple foyer. (Plywood substrate? Then I primed that, then I layed Quikset underlayment RS). It wasn’t perfect, but underlayment turned out okay.. I’m ready to start dry fitting, then setting the tile. Is it okay to use a little extra Mortar (?) in/under the areas where the underlayment didn’t turn out perfectly even, to help lift the tiles just a tiny bit in certain areas? Or any other super easy/quick fixes for this particular issue? (Learning terminology still, sorry)

  • Bert

    Recently built an enclosure around a zero clearance wood fireplace. The framing was done with metal studs and covered with cement board not drywall. I used the correct cement hardboard screw and taped the joints with proper cement board tape. I finished with two coats of Sheetrock 90 and a thin coat of drywall compound for easy sanding. The job looks great but I developed a thin crack along the cement board joint event though I taped it. This joint runs perpendicular to the studs and is therefore only supported every 16 or so inches. The span is about 54 inches long and is on a horizontal joint above the front of the fireplace halfway to the ceiling. I assume now that I went wrong somewhere but the real question is how to repair. I thought of carving a two inch channel into the Sheetrock 90 and using another layer of tape and then re coating? What are you thoughts? Thanks for any input you may have.

  • Jenn

    Hi Roger
    I am getting ready to lay thin stone veneer over Durock on our gas fireplace surround. When mudding and taping the joints of the Durock, do you let the seams cure before starting to lay the thin stone veneer?

    Thanks – your site/ posts are very interesting and helpful!

    • Roger

      Hi Jenn,

      It doesn’t matter. You can do it either way, you just have to be mindful of the wet mud as you’re tiling if you do it at the same time.