No thinset under cement board

Contractors
12yFollow

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?

7Reply
1,186 views

Most Popular Reply

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
14Reply
See this reply in the discussion

61 Replies

Jump to latestLatest
  • Mary Beatty
    Realtor · Oklahoma City, OK · Member since 2021 · 44 posts · 23 votes
    5y

    Since it wasn't specified and there are other contractors that don't use thinset I would leave it.  Going forward if you prefer to have thinset used make sure it's in your scope of work you provide your contractors! 

    0Reply
  • Bernie NeyerPro Member
    Investor · Chanute, KS · Member since 2016 · 160 posts · 60 votes
    5y

    The use of thin set mortar under the tile backer board is recommended by the tile manufacturers. This is an aspect of leveling out the floor. Small cupping under the tile backer can cause flexing and breaking of the tile. 

    That said, can you get by without it, maybe, but wouldn't you hate to not do it and have issues. There is a sub floor tile backing material called a dimple mat. It's an orange flexible material and I've seen directions indicating thin set under it.

    A doctor once told me, "You can do what ever you want, it's your body." I suppose the same is true for your house.

    0Reply
  • Gordon Starr
    Rental Property Investor · Dayton, OH · Member since 2015 · 312 posts · 273 votes
    5y

    installed tile in high end older construction. the recommended way is thick not thin. I had to cut away an old growth door jam just to fit it in. Not fun. People can trip on the steep transitions. These thickset floors are night on impossible to remove. When is a wood floor good enough to tile to? I mean assume hardwood by guided carpenters.. only the best.  thinset sticks to wood and I've done it. But am not widely experienced.

    0Reply
  • Bernie NeyerPro Member
    Investor · Chanute, KS · Member since 2016 · 160 posts · 60 votes
    5y

    All I said was that this is the way the tile manufacturers suggest doing it. Heck, I've seen guys put it right down on the subfloor.  

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

    @Bernie Neyer

    I just pulled some ceramic tile that was installed over plywood (not OSB) that was set in 1980. Very little grout cracking and no cracks in tile. Impressive considering that thinset wasn't as advanced as we have today. One thing to note is the subfloor was 1/2" plywood over 2x6 tongue and groove. Way more sturdy that todays standards. Last 2 projects I was on had cracked tiles everywhere. 2000 and 2004 builds, tile over backer. One appears to not be thin setted down and its completely destroyed. The other is thinsetted but the installer didnt glass tape the joints. Thats where the cracks are. Use of screws can help.

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

    @Robert Taylor

    Nice plug for John Bridge. Guys a legend. Ive been in the trade 21 years and use that forum from time to time. I couldn't learn the amount of info there in my lifetime.

    0Reply
  • Bud Gaffney
    Rental Property Investor · Boston, MA · Member since 2019 · 2k+ posts · 1k+ votes
    4y

    Yikes. Respectfully, you seem like you'd be DIFFICULT to work for/with. Let the PRO do the job.

    0Reply
  • Al Pat
    Rental Property Investor · Atlanta, GA · Member since 2016 · 325 posts · 253 votes
    4y

    I had several bathrooms redone on many of my properties and have not ever seen them put thin set under the cement boards of any of these. I would not make a big deal of it and move on, very unlikely you will have any issues if the tile work is done right.

    0Reply
  • David Avery
    Flipper/Rehabber · Phoenix Arizona · Member since 2020 · 1k+ posts · 686 votes
    4y

    You don't need it, it is wasted effort and money.

    Some skinny jeans college grade really thinks it is needed!

    Nope prepare the floor proper before backer board and screw it down on the outside 8-10 inches and on the inside about 12-14 inches.

    Then tile away!!!!

    0Reply
  • Robert Frazier
    Boise, ID · Member since 2020 · 84 posts · 87 votes
    4y

    If you go that route and ask him to replace it, he will never work with you again. 

    Make sure he warranties his work. That is the biggest factor. If it fails in a year, it was poorly installed.

    0Reply
Join the conversationCreate a free account to reply, vote on answers and follow this thread.
Log InJoin for Free