The Importance of a Properly Installed Backerboards

by Roger

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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Charles

Hi Roger,

1. Heard porcelain was brittle as heck. Scared now as the cutting stage is comin up. Any tips to share for avoiding chip- out at the wet saw? Should I do finish cut first, then do a regular cut? I do know to go slow and not to push the tile into the saw.

2. How to remove thresholds safely? I got a thin strip of what looks like laminate wood held down by 5 finishing nails/brads across it. I’ve got a small pry bar which worked great for the base, but not sure about the best way to proceed with the threshold w/o damaging it. I’m doing a kitchen.

Thanks mightily,

Charles

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Charles

Update: The threshold turned out to be as straightforward as the baseboard. Soon after posting, I tried just finesse it up, applying gentle pressure on either side of the finish nails and out it came.

I’m going to read up on your transitions post to get ready for handling the laminate flooring and tile transition for the kitchen.

Charles

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Roger

So no glue? Good! :D

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Roger

Hi Charles,

1. I don’t know who told you that but it isn’t true for most porcelain. If it is not annealed (cooled) correctly yes, it can be brittle. But it’s not normal. Usually only with the really cheap stuff. A finish cut and then the full cut works best on the brittle stuff.

2. Just get right under the nails and pry up slowly from there. Cross your fingers that it isn’t glued down as well. If it is you’re replacing it anyway.

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Charles

Roger,

Thanks for everything you do in diffusing tile knowledge and your great help to us going it alone. Just was wondering if Ditra, the orange mat stuff will give me the valid substrate I need to put the porcelain tile over the vinyl floor?

Thanks again!

Charles

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Roger

Hi Charles,

Yes, it absolutely will. But the vinyl needs to be removed as well as any thin plywood luan that is likely beneath it. Most vinyl is cushioned which leads to movement and traffic patterns which will eventually crack the grout. Once that’s gone you can install your ditra then porcelain.

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Charles

Thank you, Roger, once again for sharing your perspicacity and knowledge into all things tile, and doing it with humor. I think I’m gonna stick around here.

With gratitude,

Charles

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Charles

I have a vinyl floor approx. 180 sq. ft. that I’m about to set porcelain tile over. I know through reading your entries that a professional installation mandates that I should either tear-out the old vinyl floor, install backer board, and then lay the tile, or install backer board over the vinyl, then the tile.

But what if I have certain budget constraints…namely time and money…and don’t want to install any backer board?
1. Can I lay the tile right over the vinyl? Will the tile stick?
2. Is there a risk of it cracking in 8 months?
3. Is vinyl ever an acceptable substrate for tile?

I would follow all other correct methods and techniques, such as thin set under the backer, correct screw types and placement, taping of seams, thin set on top of seams, and finally thin set on top of the backer board for the substrate.

Thanks,

Charles

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Roger

Hi Charles,

1. No. If the proper thinset is used, yes, it will stick.
2. Yes.
3. No, not in my opinion. Not without backerboard over it.

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Charles

Thanks Roger. Let’s suppose for a sec I went on the fool’s errand and put the tile over the vinyl with no backerboard. Should I use modified thin set instead of unmodified to make sure it sticks?

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Roger

Yes, modified. It may then last 4 weeks rather than only 2. :D

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Angelique

I just read your waterproofing manual. Have you ever used magnesium (MgO) board rather than standard cement board? We’re planning to do our shower with the traditional method. We’re using a Tu-Tuff polyethylene vapor barrier.

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Roger

Hi Angelique,

I have used magboard. I like it a lot, it’s just difficult to find around here so I don’t use it that much.

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CDE

My mother would like to replace the original tile floor in her bathroom with new porcelain tile. The floor is 40 square feet. The house is a bi-level in NJ built in 1970. The bathroom room is on the main floor with the garage below it.

I removed a couple of tiles to see what is underneath and I had a tile contractor at the house today. He said that he would do the following:

1. Remove the rest of the floor tiles
2. Spread the thinset on top of what he called the existing “mud” base that the original tiles were placed on.
4. The floor is not flat, there is a little bit of bevel in it. He said he would “build up” the floor to flatten with what I am assuming is the thinset.
3. Put the new tiles on top of the new thinset.

Kindly seeking your thoughts and input on what the contractor said and how this job should be done properly.

Thank you for your time and assistance.

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Roger

Hi CDE,

If it is a mud bed then his technique is correct. Sounds like he knows what he’s doing. :D

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Ryan

Hi.
I’m using the redguard method for my shower. Installing half inch tile backer and applying three coats of redguard over the backerboard. I’m using mesh tape approved by redguard in all the corners and field joints. Do I still need to apply cement backerboard tape and thinset to all the backerboard prior to applying the redguard or will the redguard act to bond the backerboard sheets together?

Thanks.
Ryan.

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Roger

Hi Ryan,

The mesh tape you are speaking of is to strengthen the redgard at joints and around the drain. You still need to tape and mud the seams and corners.

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