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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Joe

Interested in installing kitchen porcelain tile with 1/2 inch cement board next to existing hardwood flooring (3/4 inch) of adjacent room. Can I get away without a transition strip on top of both and still only get a minimal height difference? Or do I need to go to 1/4 inch cement board for a more seamless transition (but end up loosing some strength)? Thanks.

Reply

Roger

Hi Joe,

You can do it without a transition strip if you want. You WILL NOT lose any strength at all using 1/4″ backer, no backer adds any significant structural strength.

Reply

Joe

Therefore, is there ANY benefit to increasing from using 1/4 inch backer to 1/2 inch, other than if need more/less height? Thanks.

Reply

Roger

Nope.

Reply

Ron

Taping the joints of hardi with what type of mesh tape? Is it the same type use in Sheetrock? I’m have a hard time understanding how this ties the sheets together seeing how the tape has such little strength. Am I missing something? And is it always important to use thinset under hardi backer? And one more question, Hardi Backer or Wonder Board?

Reply

Roger

Hi Ron,

Alkali-resistant mesh tape, it’s found in the tile section. It looks the same as drywall mesh tape, but it isn’t. The tape connects the two sheets so they move as one in a linear direction, if you try ripping a piece of that tape in half you’ll find out how strong it is for that application.

YES! It is ALWAYS important. Always.

I prefer wonder board, but both work well.

Reply

dave cerenzia

been in the tile business for 45 years. I have never taped a floor joint with mesh tape. I USE A QUATER NOTCH TROWEL AND INCH AND HALF COILROOFING NAILS . NEVER HAD A PROBLEM

Reply

Roger

Well hi Dave,

WHY THE FUCK ARE YOU YELLING ON MY BLOG???

Being in the tile business for 45 years you may not realize this – typing in all caps constitutes yelling on the internet. Please don’t yell at me, it tends to piss me off.

I’m assuming that you’ve never had anyone call you back in 45 years to tell you their floor is cracking. I’m also assuming that’s why you’re assuming you’ve never had a problem. Good for you – ignorance IS bliss sometimes, isn’t it?

Just because no one has called you back to fix something that you’ve fucked up doesn’t mean you have never had a problem, it means those people didn’t call you to fix what you fucked up. Get it? :D So take your ego and your magic coilroofing nails and fuck off with ‘ya.

Now, if you would have bothered to read around a bit before attempting to troll ME on MY website, you may have discovered a few things:

First, everyone who reads here regularly already knows you’re full of shit. It’s the old ‘I’ve been doing this for a thousand years AND NEVER HAD A PROBLEM’ line. It’s bullshit. You know it, I know it and all my readers know it.

Secondly, I am more than happy to have a RATIONAL conversation with any point I make with which you may disagree. But if you come onto my blog and act like an ass, or ‘yell’ without provocation, that particular conversation is off the table.

Lastly, any installation methods I state, or installation methods I repeat, including taping floor joints, are standards set forth by the TCNA and ANSI tile installation standards handbook, something with which you are obviously unfamiliar.

Tell you what, if you’re so adamant about not having any problems, ever, why haven’t you shown up at a TCNA technical committee meeting and made your case? We would have listened. But you didn’t do that, did you? Please, continue to NOT tape your seams, continue to do things improperly, continue to believe that you’ve NEVER HAD A PROBLEM with those improper methods.

It keeps guys like you happy and guys like me in business.

Have a fabulous weekend! :D

Reply

tauran

Roger, do you mud over hardi backer screws or do you just need to tape and mud seams?

Reply

Roger

Hi Tauran,

Just the seams.

Sorry for the delayed response, my spam filter went ape shit last week for some reason, I just found your comment in the spam folder, I hope the answer found you in time.

Reply

joe

Replacing vinyl in kitchen and sunroom with porcelain. Sits currently about 1/2 inch less than hardwood floors in adjacent room. Under vinyl I have luan then about 3/4 inch OSB above floor joists / crawl space. Very slight unlevel/hump in one area. Removing vinyl and luan. Received 3 quotes: one said 1/4 inch wonderboard, another said 1/2 inch wonderboard, and one quoted Strata Mat on top of OSB with no additional plywood or board. Making sense? Any preference? Best for customer? Any cost differential?
Thanks.

Reply

Roger

Hi Joe,

Any of them will work, but they ALL need an additional layer of 1/2″ ply beneath them.

Reply

Bill

Hi Roger,

I’m building a walk in smoke house with 2×12 Walls (reclaimed roofing materials). Because of the fire concern and cleanability I want to line the inside with concrete board and ceramic. The idea is the inside should never get above 220 degrees so unless there is a grease fire I should be safe.
So my question is about the vertical walls and ceiling, do I put a moisture barrier (aluminum) behind the concrete board and do I just put on thin set and go or do I need something other than thin set for the heat?

Reply

Roger

Hi Bill,

Just thinset and go. Using aluminum behind the backer would defeat the purpose anyway. :D

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Bailey

Hi! We laid Hardibacker board over a wood subfloor a few days ago. When tapping the seams, I noticed that one corner of the backerboard is quite a bit unlevel. It is too hard now to redo. Can I simply hammer that corner down, vacuum up and loose material and apply more thinset to even the surface out?

Additionally, what is the consequence if 4 corners of the backerboard happen to line up? I have a stubborn husband that wouldn’t listen to me on that one so he will be re-doing the floor if there are any issues.

Thanks!

Reply

Roger

Hi Bailey,

Yes, but don’t tell anyone I told you that. :D Four corners in one spot creates a weak spot in your substrate where it is both not as sturdy as the rest of the floor as well as a pinpoint area where expansion of all four sheets could cause an issue – even when taped and mudded.

Reply

Nick

I am planning to apply mesh tape and thinset to the joints and seams of the cement board in my shower, but I would also like to use one of the liquid waterproofing products in those areas as well. The product’s instructions mention the optional use of a fiberglass reinforcing fabric. My question is – could you skip the use of the mesh tape when applying the thinset to the joints and seams if you are embedding this fiberglass fabric in the waterproofing product in those same areas? Or would you apply both the mesh tape with the thinset and then apply the fabric and waterproofing over the whole lot (seems like you could end up with quite a hump)? Or skip the fabric all together? Thanks – I enjoy getting my education with your mix of knowledge and humor. Keep up the good work.

Reply

Nick

Submitted my question before scrolling through the comments – is Ryan, in the last post, asking the same question? Sounds like your answer is to use both the mesh joint tape with the thinset application and the fiberglass fabric with the waterproofing product.

Reply

Roger

I told Ryan the same. You normally won’t tape and mud the wall/floor transition or the drain, so you still need the fabric there with the liquid.

Reply

Roger

Hi Nick,

Only use the mesh tape when you tape and mud the seams (just using thinset doesn’t do what it needs to). Once that’s cured you already have the fabric reinforcement over the seams. You should still use fabric reinforcement at the wall/floor transition as well as around the drain.

Reply

Julie

Hi Roger,

Do I need to use plastic vapor barrier behind 1/2″ Hardibacker board in my tub/shower combo if I’m using Kerdi over the Hardibacker?

Thanks for your help! You’re awesome!

Julie

Reply

Roger

Hi Julie,

Nope.

Reply

anthony

Hi Roger,

I posted a few months back regarding our travertine stone tile floors cracking in near exact 4’x8′ patterns matching the OSB panel joints. This occurred in 2 bathrooms and a laundry room. I just removed a tile and checked subfloor panels (from crawlspace access) – my findings are included below.

Facts:

Tile floor assembly has single-panel 23/32″ OSB T&G subfloor with 1/4″ CBU over wood framing (2/12″ EW Joist, 16″OC) that’s better than L/720.

Cracks formed directly over single subfloor panel joints (4’x8′ pattern) and are indented, concave depressions about 1/16″ max depth.

The cracks weren’t observed until ~ 6 years after tile installation (new home) and slowly formed over this past year.

We lived in home full-time for first 3 years (two adults, foot traffic light), but for the past 4 years we have only utilized home on weekends (very light traffic). While away we use HVAC to keep home between 50F-82F.

Builder did not install a vapor barrier in crawlspace and the home is on a sloped lot. Moisture levels in crawlspace were so high they distressed adjacent hardwood floors. We installed a vapor barrier and increased crawlspace ventilation about 2 years before tile cracks started.

Tile was hard-grouted at perimeters instead of using expansion joints.

Findings when tile removed and subfloor checked:
a) As suspected, cracks were directly above subfloor panel edge and end joints;

b) Thin-set mortar beneath backer board was extremely thin, 1/16″ thick at best.

c) CBU seams were butted, not gapped, however seams were taped.

d) CBU board was cracked (not at seam) beneath tile crack. So was thin-set of course.

d) Backer board was not wet sponged as evidenced by significant cement dust which made for poor bond with thin-set.

e) “Patty” method used on top of troweled thin-set (~3/32″) beneath tiles – one “dab” at corners and one in middle of tile. Coverage was only about 30%! (Hard to believe this didn’t cause tiles to crack early on!)

f) Subfloor panel edges were checked from crawlspace access. Edges beneath tile cracks are warped or buckled. Buckling at the panel edges is a downward sagging, concave shape measuring about .065″, very similar to tile indented fractures. Couldn’t check panel ends since the joists hide them. Buckling likely occurred as OSB dried out after the vapor barrier and ventilation was increased.

I would appreciate your insight as to:
1) why cracks formed only above subfloor edges and not over CBU seams as well;
2) Why it took so long to crack given how poorly it was installed, and
3) What would you suggest as best installation method for new stone tile assuming we re-use 3/4″ OSB subfloor.

Sorry for this lengthy post. I’m still puzzled why the floor took so long to fail, especially given how poorly it was installed, and wanted to provide you with all the details. Shorten for posting as you like.

Looking forward to your inputs.

Thanks,
Anthony

Reply

Roger

Hi Anthony,

It seems to me that the amount of time is due to the time it took for the moisture which was being absorbed by the subfloor (due to lack of vapor barrier) to warp the edges enough to cause significant failure of support beneath the backer in those areas. The reason it cracked over the subfloor rather than the cbu is because the cbu seams were taped and mudded, thus a monolithic structure at that point.

I have absolutely no idea why it took so long to fail, but as I’ve always said, it will fail if the five-spot method is used on a floor – EVERY TIME.

Since you’ve installed a vapor barrier I believe you’ve essentially eliminated the source of the problem. Any proper method would be just fine with your framing specs. I would probably do an additional layer of 1/2″ ply over the osb, then ditra, then tile.

Reply

Anthony

Roger,

Thanks so much for your input and timely response. I like your idea of adding plywood underlayment and ditra, so we’ll likely go with that. Your passion in your work and commitment to help others solve problems are inspiring. Keep up the great work as it helps many of us sleep a little better at night.

Thanks again,

Anthony

Reply

Andrew

Hi Roger,

Very helpful site! Thanks!! Quick question, we are putting in a new neo-angle shower with a fiberglass base and tiling the walls. I installed hardiebacker 500 over the weekend and tape the joints last night with proper cement board tape. My question is do I need to mud (thinset) the joints prior to tiling or is the thinset used when tiling sufficent? I was thinking I needed to do it seperate, but someone mentioned that you can combine that step. Thanks!

Reply

Roger

Hi Andrew,

You can do it as you set the tile.

Reply

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

Reply

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

Reply

Roger

So no glue? Good! :D

Reply

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.

Reply

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

Reply

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.

Reply

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

Reply

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

Reply

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.

Reply

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?

Reply

Roger

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

Reply

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.

Reply

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.

Reply

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.

Reply

Roger

Hi CDE,

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

Reply

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.

Reply

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.

Reply

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