Removing Thinset from Subfloor

Discussion in 'Remodel Forum & Blog' started by Baron, Jul 24, 2008.

  1. Baron

    Baron New Member

    Messages:
    59
    I am replacing floor tile and is was bonded directly on the subflooring with thinset.

    I'm in the process of removing the old tiles -- and need to prep the subflooring for the new tiles.

    Any ideas on the best way to remove the old thinset from the subflooring??

    Thanks.
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,304
    Location:
    Cave Creek, Arizona
    thinset

    Probably the only way is with a hammer and chisel and then a scraper.
  3. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Hammer and chisel if you have the rest of the century to finish this job, otherwise consider an angle grinder, or a larger floor grinder ( HD rents them)
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    You can get a razor scraper with a long handle at one of the big box stores. 4-5" blades, buy extras!

    Depending on how even the layer is, you might just put your new decoupling layer (cbu ) on top of it with new thinset. The existing stuff must be well adhered. If you wanted to use a membrane instead (like ditra), you'd probably want to get the old stuff off first. The thinset under cbu is just to fill voids and give 100% support, but the thinset under a membrane is what holds the membrane in place.

    Check out www.johnbridge.com for expert help on tiling.
  5. Baron

    Baron New Member

    Messages:
    59
    I'd like to get it off as quickly and cleanly as possible with minimal dust.

    I'll try the scraper method first and see how it goes.

    Also I'll check with Home Depot -- (as suggested) on a Floor Grinder if the scraper method isn't going well. Thanks.

    Which leads me another questions:

    Do I need to put thinset between the Hardibacker board and subflooring OR
    can I get away with nailing/screws between the two?
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    All cbu manufacturers REQUIRE thinset (that I know of anyways). The thinset can be cheap dryset mortar (i.e., unmodified), since its sole purpose is to fill voids and provide 100% support. The nails or screws are what hold it down in this case, not the thinset (although it does somewhat). Make sure to also use the proper mesh tape on the seams. that can be installed during tiling so you don't generate speed bumps. Taping cbu seams is entirely for strength, and not for appearance like it is on drywall, so no tapered seams...just embedded in the thinset while tiling is easiest. Make sure the mesh tape is spec'ed for use with thinset...that for drywall will eventually disintegrate in the alkalai environment.
  7. Baron

    Baron New Member

    Messages:
    59
    Thanks Jim for the response.
    I'll do just that -- plus check out the website link you posted.
  8. statjunk

    statjunk DIY Senior Member

    Messages:
    542
    If you can't put up with the increased floor height by going over it with thinset and cbu then you can try a chipping hammer. There are these flat blades that have a real sharp thin edge that are used to remove thinset and tile. It's very think like sheet metal. Works pretty good.

    Tom
  9. Baron

    Baron New Member

    Messages:
    59
    So -- I can just thinset and cbu over the exisiting thinset??
    If yes -- I'd rather do that than trying to remove it.
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    Yes, if the thinset is firmly attached and moderately level, you can add more then attach the cbu. BUT, keep in mind the original layer may crack and because it is hard, make it really hard to get the cbu to lay flat without voids. The whole reason for the cbu is two-fold: make a compatible bonding layer for the tile and decouple with the floor beneath. The reason for the thinset is to ensure 100% support.

    If the thinset is fairly smooth and level and properly bonded to the subfloor, I'd consider installing Ditra from www.schluter.com over it. This is relying on the thinset to hold it in place so there'd be no likelyhood of cracking the old, hardened thinset when you add the screws or the nails. If the existing thinset is NOT firmly bonded, though, there'd be a compromised connection holding the Ditra in place.

    A rubbing stone could probably take off any high spots. It's better to remove it, though.

    In the end, though, it might be less time consuming to just replace that layer of ply with new - less time, better end result; known condition.
  11. GregO

    GregO New Member

    Messages:
    73
    Location:
    Virginia
    thinset

    What Jim said. Just also make sure to check your floor specs for tiling. I like the idea of true thinset, then CBU. You can even install Ditra on top of that if your structure is somewhat unknown. But ideally, you want proper plywood and joist support for a long-live tile job. As mentioned earlier, do check out johnbridge.com for more...Greg

    PS Jim, about thinset underneath CBU- surprisingly, this used to not be part of the installation instructions years ago, but has obviously since changed and for good reasons.
    Last edited: Jul 30, 2008
  12. Baron

    Baron New Member

    Messages:
    59
    Finally got to removing the thinset from the subfloor.

    Ended up renting a Orbital Floor Sander from HD. $29 for 1/2 hour.

    It did a great job -- but, a little messy with the dust.

    Now I'm ready to lay the cbu. I'm looking into either the Hardibacker, Ditra, or Easy Mat.

    Thanks for everyone's suggestions.
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