No thinset under cement board

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No thinset under cement board

Michael Herr
Peoria, IL · Member since 2011 · 365 posts · 182 votes

Just went to inspect some work and noticed they weren't using thinset to lay down the cement board under porcelain tile.

When I asked the contractor, he asked his flooring guy who had been doing tile for 25 years and "never puts thinset under cement board".

Our agreement was to put down cement board and tile.

Nothing was specifically said about thinset. The manufacturer dictates to use thinset between subfloor and cement board.

It is 1/2" durock over 1" nominal thick plank.

For the record, this is my first time really contracting anything. It's been all me and cheap DIY/Craigslist hacks before this, so I am willing to take pointers on how I could have/should have done something different.

Should I have been more specific in work instructions?

Should I demand he redo the job to what I think is the right way?

Should I meet him in the middle and pay a bit more?

Most of the 375sq ft of tile is already down.

What would you do?

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Tom Meade
Real Estate Investor · Boston, MA · Member since 2013 · 108 posts · 71 votes
12y
I've never used thinset under cement board, for what it's worth. I'm not sure you really have standing to make him do it the way you think is right...you say yourself you're a DIY guy and he's the pro...tread carefully
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  • Jim Goebel
    Real Estate Investor · Des Moines, IA · Member since 2016 · 922 posts · 533 votes
    7y

    We recently used thin beads of construction adhesive under backer board (permabase) brand with full knowledge that thin-set was what was recommended.  However, I was directly managing the work and I'd place a strong bet that the construction adhesive will do everything that the thin set would.  As someone mentioned before, screw spacing I think is one of the most important considerations.  The construction adhesive approach was easier and you'll have to ask me in 10 years about my decision.

    However, in general I think including the statement to 

    'follow manufacture recommendations' when bidding out / contracting is a good idea.  At worst it gives you some leverage in negotiating resolutions to situations like these.  I've been through quite a few where something is caught after the fact and you have some tough calls and have to find a way to navigate with the contractor.

    0Reply
  • Bernie NeyerPro Member
    Investor · Chanute, KS · Member since 2016 · 155 posts · 60 votes
    7y
    For everyone who said they never used thin set under cement board. The directions for all the tile manufacturers is to use thin set under the cement board when going over wood sub flooring. The reason for this is usually there can be voids between the cement board and the sub floor. Directions indicate you should use a 1/4 inch trowel.
    2Reply
  • Sean H.
    Developer · NC · Member since 2019 · 211 posts · 112 votes
    7y

    Yes, it is recommend. It helps hold the cement board in place long term, and helps level out the cement board. Unless it was agreed upon before the job to skip that step, i wouldn't appreciate someone skipping the step. Also, use 1/4" on floors, 1/2" board on walls. 

    3Reply
  • Gordon Starr
    Rental Property Investor · Dayton, OH · Member since 2015 · 312 posts · 273 votes
    6y

    First the subfloor then the backer board then the tile all screwed in and mortered down. Takes forever, back breaking, costly, and I pity the man who has to take that floor out! Not to be all negative since you probably heard the old joke.. laying tiles is like laying women.. you do it right the first time and you can walk all over them for the rest of your life

    2Reply
  • Jack I.
    Member since 2019 · 43 posts · 24 votes
    6y

    Flip the coin and ask yourself the question the other way ( I am a trained engineer and that is what we are taught to do ). If you apply thinset between the wood flooring and the backer board ? It is not thick enough to provide physical strength to keep the backer board from bending...so what is the function ? 

    1Reply
  • Benjamin Tighe
    Medford Oregon · Member since 2019 · 85 posts · 65 votes
    6y

    To fill voids due to uneven surfaces so that the backerboard will not have deflection and bounce if the fastening system is not 100% capable of eliminating movement. Many have gotten away without thin-setting backer down and it does work better with the RIGHT screws. I can thin set backer and shoot it down with a coil nailer faster than someone can screw it down without thin set and know that my system will be more forgiving to the existing conditions of the floor. We are talking about T&M cost difference of pennies per SF. The companies that make these products spec how they are to be used for a reason. Just because something can be done, has worked in the past, or makes sense on paper, doesn't mean its the best way. FWIW, every time I have seen someone cutting the corner of using thin set under CBU, the laziness has shown through out the rest of their work. TCNA has an insane amount of info and research around the tile industry. Quality tile work isn't easy or cheap, don't try to change that.

    1Reply
  • Pawel S.
    New Britain, CT · Member since 2016 · 2 posts · 0 votes
    6y

    You might get a better response next time if you refer your contractor as Mr. "DIY/Craigslist Hack".

    0Reply
  • Forrest Faulconer
    Real Estate Agent · Oklahoma City, OK · Member since 2020 · 471 posts · 462 votes
    5y

    Well I am not a tiler, but did just tile my entire kitchen. I had no idea putting thinset under the cement board was the recommended thing to do, however I don't believe most tilers do that, at least I have never seen it.

    0Reply
  • David Avery
    Flipper/Rehabber · Phoenix Arizona · Member since 2020 · 1k+ posts · 686 votes
    5y

    Its not needed!

    Done 45 years of it

    1Reply
  • Stu Bidasso
    Member since 2020 · 3 posts · 3 votes
    5y

    I've done tile for 30yrs (since before Hardybacker). I used it when it first came out but always used 1/4 inch  on floors and 1/2 for walls. I read the instructions and ALWAYS thinsetted before installing and nailing it. I also taped the joints with recommended mesh tape. I have never had a failure, but I have repaired some floors that were not taped on the seams. The tile had cracked right down the seams of the Hardybacker.

    0Reply
  • Tom Wolfe
    Member since 2021 · 3 posts · 2 votes
    5y

    I can't understand why so many people here say they just didn't know that you need to put thinset under backer board. Do people really spend hundreds or thousands of dollars and days of their lives without taking a few seconds to read the instructions to make sure their money and time aren't wasted? Do these people think that they were born with the innate knowledge of how to install tile? There is only one reason to skip a step -- to make installation easier. Who cares about five or ten years down the road? They'll be long gone by then. 

    If it's worth doing, it's worth doing right  

    1Reply
  • David Avery
    Flipper/Rehabber · Phoenix Arizona · Member since 2020 · 1k+ posts · 686 votes
    5y

    its not the backer board that makes the tile crack.  It is the sub floor that is not level or secure.

    You never put backer board on a floor that is not ready for it.

    There is a tool called a level and it has a bubble on it,  it is used to level construction jobs. some contractors even have a 8 foot level.

    This is the step the  skinny jeans people don't mention!

    ps  never nail backer board,  there is  a tool called a screw gun that will install the screws that 

    I encourage every 6-8 inches on the outside edges and every 10-12  inches in the middle.

    If you know construction and tools it is very easy to properly install backer board.

    Ready instructions versus doing the work is miles apart!

    Have laid more square footage of tile then could be stored in a college class 10 x 20  by 8 feet high!!!

    0Reply
  • David Avery
    Flipper/Rehabber · Phoenix Arizona · Member since 2020 · 1k+ posts · 686 votes
    5y

    Go ahead and correct  my  spelling while your trying to do Real Estate!

    0Reply
  • Tom Wolfe
    Member since 2021 · 3 posts · 2 votes
    5y

    And if the framers used a level and did the job right then you'll find the job of tiling that much easier

    1Reply
  • Paul Morgan
    Member since 2021 · 1 post · 1 vote
    5y

    Reply to David:

    I have also installed a fair amount of tile since that was my trade. I have one of those things with the bubbles that you mention as well as one of those screw guns that you mention. However I have NEVER used them on Hardyboard over a wood floor. I do, however, have a few magnesium straight edges and a pneumatic roofing nailer. I also have a thing called a notched trowel and a 1/2 in. drill with a mixer on the chuck that I use to mix thinset.

    You might not know it, but you can install tile on a slope where that bubble thing might be useless. Just because a floor is level, it's irrelevant. What IS important is that it is FLAT. This is where the thinset comes into play. It helps to fill in the low spots. The nail gun is 10 times faster than the screw gun and does the same job. If you ever have to take out one of your own tile jobs because the tile cracks down the joints of the Hardyboard as a result of not being thinsetted and the joints taped, you will cuss that screw gun. Besides, how many floors in Arizona are not concrete?

    1Reply
  • Tom Wolfe
    Member since 2021 · 3 posts · 2 votes
    5y

    yes even is what's important. Horizontal/level doesn't matter. Just ask someone who has tiled a vertical wall :)

    0Reply
  • Benjamin Tighe
    Medford Oregon · Member since 2019 · 85 posts · 65 votes
    5y

    Thinset is not used to bond to the subfloor. Demo any tile job over osb and youll know what Im talking about. Its used to fill voids. Taping joints is not to prevent movement. Its done to isolate the movement so that it doenst reach the tile. Look into crack isolation techniques for concrete. Screws are better than nails but without the thinset bed, its half done. Even a seasoned house flipper wont have their work scrutinized like a professional tile setter. How long does a flippers work have to hold up? If it looks good for a year and nobody called you when it failed, was it still done right? Im about to get some massive overtime hours replacing several thousand feet of tile in a car dealership. Job was done 6 years ago and to be honest, looked pretty good. Setters did not use the appropriate amount of thinset. Probably saved 3 grand in time and materials. With our whole crew on overtime plus materials, this avoidable fix could hit 10 grand if all goes well. If not, the liquidated damages to the dealership, in addition to our part, can make this a 30k loss in the span of a week. Im sure that feels great after the last year. But hey, it looked good when they moved in and everyone got paid.

    Just to put it in another perspective, how many people here have had to deal with wrinkled carpet? How about seams failing? Im willing to bet damn near everyone. If installed correctly, even cheap carpet should last 10 years without wrinkles or seam failues. Problem is, the shortcuts dont show up in the first year. By the time they do, the check in cleared and the warranty is up. Lets pretend it was due to tenants, professional cleanings, or quality of the materials. Thats all BS. Its because guys use a pick stretcher or kick it in instead of using tubes when stretching. Its because properly cut and sealed seam edges take more skill and time. Its because doing it right costs more money.....

    1Reply
  • Bernie NeyerPro Member
    Investor · Chanute, KS · Member since 2016 · 155 posts · 60 votes
    5y

    Let  me add this again, the tile manufacturers recommend it. Let's unpack this, it means that if you don't and the tile breaks, they won't warranty the tile. On good floors you can get away without it. On older houses, you simply can't.


    Now, in the old days, you never used tile backer because you didn't have it. You actually used thin set mortar. There was a process that was called dry mix. You would spread the mix damp and set the tile then use a sponge wetting the tile down creating a wet set mortar that  would then set harder. 


    Because some tilers do it WRONG, doesn't mean you should. End Of Discussion. 

    1Reply
  • Stu Bidasso
    Member since 2020 · 3 posts · 3 votes
    5y

    Yep. Back in the old days floors were recessed in anticipation of a dry-pack mortar bed. Unless you are building a custom house, where you can prepare the floor when it is framed, chances are that you will use some sort of a backer board or Schluter product to set the tile. I agree that a mortar bed is preferable, but unless you have at least 2" recess, then an alternative is almost imperative. Just read the manufacturers' instructions and act accordingly. 

    0Reply
  • Jack I.
    Member since 2019 · 43 posts · 24 votes
    5y

    Wow, this thread is still going after all these years.... I just re read them all... why would anyone ever tile a floor when we have luxury vinyl planks now... tiles crack over time, tiles pop over time, grout gets dirty... lvp keeps going and going.. 

    1Reply
  • Sarah Helene Lavertue
    Flipper/Rehabber · CT · Member since 2021 · 1 post · 0 votes
    5y

    I honest have never used thin set AND cement board together, usually one or the other for me. Unless the floor structure is of concern, or the tiles are so large they are prone to breaking if there is any fluctuations in the sub floor. But it seems like overkill to me. Love your passions to do it right! 

    0Reply
  • Michael King
    Rental Property Investor · Navarre, FL · Member since 2019 · 913 posts · 640 votes
    5y

    I just redid my hearth. I used thinset, hardie backer, then thinset the tile to the backer. Reason I used thinset: it was written to do so. An advantage of it is that I could fill the imperfections of the wooden floor (and there were tons of them). The hearth is the flattest and most level part of our den. Unfortunately it is so well laid, it stands out like the proverbial. 

    0Reply
  • Nick Rutkowski
    Rental Property Investor · Ithaca, NY · Member since 2015 · 1k+ posts · 1k+ votes
    5y

    @Michael Herr

    Leave it alone, you’re fine. Next time make sure your contractor reads directions from the manufacturer. To be honest, there are many ways to do construction. Some ways are better than most. What are you using for waterproof?

    0Reply
  • Clayton Eva
    Member since 2021 · 1 post · 0 votes
    5y

    So I am an elderly homeowner who has done two bathroom projects in my residence. The first project was a first floor bathroom renovation, which included gutting out the bath and going with a new tub, toilet vanity and closet. On that particular job, I stripped the floor down to the 1" x 8" pine planking (house was built in 1950). I laid down 1/2" Durock, screwing on center as required by the manufacturer using sheetrock screws. The subfloor planking was irregular in height (3/4" to 7/8") and it was pretty knotty with some bouncy areas felt when walking around. I asked a building inspector from the city of Providence, RI what I should use for tiling the floor and he recommended 1/2" Durock. I recently gutted that same bathroom a second time and over 30 years later, there wasn't a cracked tile to be found and I have to say there was good adhesion observed when going through the work of using a hammer drill and tile spade when removing the tile and Durock. My second bathroom floor was laid tile 20 years ago. On that floor, 3/4" plywood was the subfloor applied by a contractor. I again put down 1/2" Durock using the recommended fasteners. The second floor bathroom has no damaged tile to this day. So I am now into the second makeover of my first floor bath, and a friend of my son is a tile man who really likes the Shluter products. I have over 50 years (54 to be exact) service between two ceramic tiled floors that have had Durock as the underlayment. On the current bathroom project, I removed the pine planking and glued and screwed down Advantech sub flooring. The floor is substantially firmer, having 2 x 10 floor joists and Advantech is awesome. In doing some research tonight and seeing the recommended application of thinnest under the Durock, I was trying to figure out what to do. In reality, I have enough history of the Durock performance to put it down over the best sub flooring in my house to date without the thin set application. I will obviously use the recommended screws at the minimum spacing recommended.

    Clay Eva

    0Reply
  • Curtis Mears
    Property Manager · Raleigh, NC · Member since 2014 · 728 posts · 596 votes
    5y

    I am no expert so will not way in on the thin set. Seems many do not use it. I would draw up a document for them to sign acknowledging they are not following manufacturer guidelines and if there is an issue because of it, they will warranty their work. They may elect not to sign, which would make me more nervous.

    0Reply
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