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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Matt

Hello Roger,

Thanks for all of your help – your books are great.

I’m now revisiting a kitchen tile installation I did before I knew about your website. Hardibacker is the substrate and was installed according to instructions (proper screws, taping and thin set underneath).

When I originally installed the tile, the thinset dried very quickly and a few years later a tile loosened. I pulled up all tiles (12×12 granite) assuming this was a widespread problem. 98% of the tiles came up very easily, leaving all thinset on the hardibacker which was often then easily chiseled/scraped off the hardibacker. For the remaining 2%, the tiles were soundly bonded and either took the top layer of hardibacker with it or seemed to delaminate the top layer of Hardibacker.

I would really like to avoid removing all of the hardibacker. Is there a way to use the existing hardibacker by repairing the areas where the top layer of the hardibacker sheet was removed and repair areas where it seems like the top layer of hardibacker may have delaminated from the other layers?

Thanks if advance for your help!!

Matt

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Eliza

Hi there and thank you for an excellent resource. I have unfortunately only discovered some of this information after doing my installation of hardiebacker. I have my hardiebacker thinset& taped& “mudded”; problem is that I didn’t know about the gap principal between hardieboards. I have them pretty near flush. I am worried about some very subtle swelling at the joints although nothing seems too drastic. Should I rip out and redo before installing floor tiles ( which are 12×24 each)?

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James Hindle

With backer board that is glued and screwed to the floor every 6″ to 8″, it seems a little redundant taping the boards to help prevent them from moving. Is there a better reason for the taping?
James Hindle
thehindles@gmail.com

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Antoine Brathwaite

Hi! I’m doing a remodel on my bathroom and installing backerboard around my tub. The issue that I’m having is that the drywall is 5/8 but I can’t find 5/8 backerboard. The closest I have found is 1/2. What are my options ?

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Roger

Hi Antoine,
You’ll need to shim out your studs by 1/8″ behind the backerboards.

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maria witt

Tiling a shower and our niche box is about 1/4 inch thicker than our backer board. We are planning 4×16″ subway tile hung vertically, how do we correct for this hump?

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Roger

Hi Maria,

Most premade niches are 1/2″, is yours not? Or did you actually use 1/4″ backer in your shower, because if you did you need to remove that ad replace it with 1/2″ backer.

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FloorOgre

What about using galvanized staples (a lot of them) in your floor hardiboard? I’ve torn up a few and it’s not easy to do. The staples stay behind when the underlayment comes up. I’m talking 18 ga. Shot it with a pneumatic stapler. Really fast.

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Roger

I wouldn’t, but it’s your floor – do what you want. :D

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Justun

What to do with a real high corner with backer board

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Roger

You mean a corner that sticks out more than the surrounding substrate? You need to figure out why it does that. Either remove some of the stud which is causing it to do that or shim out the surrounding substrate to meet up flush with the ‘high’ backer.

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Michael Scott

Hello Roger,

Thank you so much for having the formost resource on the web for all us homeowners that are trying to diy tile with more energy than knowledge! I tilt my beer to you and will keep an eye out to make sure my dog does not catch fire.

I have a (wall) corner of hardibacker 500 that has cracked slightly around both the original screw and the second one I put in after adding some blocking (by sliding underneath the board) to the stud to try to gain a spot for another screw. The rest of the board is solid, and this corner is going to be behind a vanity where it should not be bumped.

The board is horizontally mounted, and this corner is an inside corner.

Can I use thinset and tape to try to strengthen this board, or do I need to take the whole thing down?

I tried to upload a picture, not sure if it worked.

Thank you so much,

Mike

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Roger

Hi Mike,

Yes, just thinset and tape and it’ll be just fine.

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Michael Scott

Awesome! Thank you sir. I may have also screwed up another aspect of this horizontal board and the one below it. I noticed a slight lip between the upper board and the lower board.

Closer examination revealed a slight hump on the middle stud by the upper edge of the lower board. This is indicated by the gap between the level and the upper board in the picture. Is this something I could overcome when I thinset/tape the seam by feathering out the thinset? I was planning to use smaller tile or mesh mosaic on this wall anyway, If that helps any. I can try to get an exact measurement, but I know it was so small, I was having difficulty reading it due to the metal end of the tape measure. I didn’t know if you had any general rules for out of plumb backer board joints vs tile size?

Thank you again,
Mike

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Roger

The smaller the tile the more difficult it is to overcome. With smaller mosaics you do want to tape and mud that, then feather the thinset out so it at least gives the appearance of being flat.

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Michael Scott

Thanks Roger, I really appreciate it. Might go with something larger then since everything is still up in the air for design. Will be purchasing your pre-made shower pan / topical membrane guide once my cast iron shower pan arrives (working on opposite side of room now).

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Jeff

How many times am I required to mud the tape joints

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Roger

Hi Jeff,

Just once.

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Carolyn

How important is the 1/8″ spacing between boards in a tub surround?

Also, can you place one board directly over another horizontally i. e. two boards 3’0″ x 5’0″ makes up the entire surface to be tiled, or do you have to cut boards and stagger to allow for vertical movement?

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Roger

Hi Carolyn,

It’s fairly important. What’s the issue?

Yes, you can place one directly over the other, that’s why they’re sized like that. You’re only required to stagger when a vertical seam is necessary.

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Annie

Hi! My husband I moved into our new house in summer. We knew that grout of our bathroom floor was getting loose in parts. He finally got around to re-grout this week and discovered that whoever tiled the floor did it right over the subfloor. (He could see wood when he removed the old grout.) We were terrified and started searching the net frantically to see how bad our situation is and came across your page. So my question is, should we rip up the floor and start all over again? Or is there any other way?

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Roger

Hi Annie,

Yes, you should rip it out and properly install a floor. You can regrout it, but you’ll end up having the same issue shortly down the road. Wood always expands and contracts A LOT. Without a proper substrate between the wood and tile you’ll always have issues.

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