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My husband and I have a huge issue right now. Some guy messed up our tile job completely, so we are removing it all and replacing it ourselves (should have done it ourselves in the first place). The tiles all popped up in whole pieces- the “contractor” did not back butter the tiles. Instead, he put all the thinset on the backer board that we just recently put down ourselves with screws (and taped and mortared the seams). Now all of the thinset is stuck to the backer board. We need to use this backer board again. How the heck do we take this stuff off? It’s really thick !! We’re talking about 320 sq ft.... Would it be okay if we sanded some of it down and then poured a self leveler over it? Please say yes.... Thank you!enter image description here

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    FYI, no professional installer "back-butters" floor tile. That would be absurdly slow and is completely unnecessary. Something else went wrong here, like a bad mortar mix or incorrect product selection. Looking at the mortar pattern, either it was mixed too dry, left to sit too long, or the tiles simply weren't pressed in well. (A little squish and squirm is critical.) – isherwood Oct 14 at 13:48
  • That doesn’t answer my question at all, and you are wrong about not having to back butter. – Rosemary Oct 14 at 13:54
  • It wasn't intended to answer your question (being a comment), and no, I'm not wrong. I built homes for several decades and have done many tile jobs myself. Never a single tile pop. – isherwood Oct 14 at 13:56
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    I've edited your title (again) to make it more generic. We serve a global user base, so brand names don't always translate well (and are often unfamiliar to some users). It's better to use standard industry terms. You'll get more response, too. – isherwood Oct 14 at 20:31
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    You don't have to back butter. You just need +80%. - "ANSI A108.5 section 2.5.3 states: “Average contact area shall be not less than 80% except on exterior or shower installation where contact area shall be 95% when not less than three tiles or tile assemblies are removed for inspection. The 80% or 95% coverage shall be sufficiently distributed to give full support of the tile.” – ceramictilefoundation.org - looking at the trowel marks still there, it wasn't +80% – Mazura Oct 16 at 2:38
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For a small area, a grinder with a silicon carbide wheel will clean thinset off, but it is real messy. For your 320 sq ft area, it could be done, but I would be inclined to pull the backerboard up.

Was the backerboard thinset to underlayment plywood or something like that?

If height is not an issue, you might consider thinsetting new backerboard to the existing, after using a grinder to level out the high spots.

Sorry I cannot offer a more definitive solution; you are in a hard spot.

  • Thanks. Yes the backerboard is on the subfloor with thinset between. It would really pain us to take it off since we just put It down a few months ago. Put so many screws in each piece and even mortared the seams .... do you think a self leveling compound would be out of the question instead of putting more backer board ? I appreciate your help – Rosemary Oct 14 at 12:48
  • I would not rely on a self-leveling compound. Just my take, and I don't have engineering data to back it. I would level the existing thinset with a grinder to get a uniform height, and put new backerboard on. I would butter the two backerboards together, so that things are a firm sandwich. – mongo Oct 14 at 12:53
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I would use a scraper like this (blade nearly perpendicular to floor). Pull rather than push.

enter image description here https://www.homedepot.com/p/Hyde-2-5-in-Wide-2-Scraping-Edges-Scraper-Blade-Tungsten-Carbide-10620/100145658

Be sure not to repeat the mistake. Level and/or use larger notches.

  • This looks like a tool that might help us. We’ll check this out today. Thank you – Rosemary Oct 14 at 12:49
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I had this same issue when I replaced my kitchen ceramic tile with hardwood 20 yrs ago. I tried several products before finally finding one that works from Home Depot. I am truly sorry I can't recall the name/brand--but it did work well in dissolving the thinset. I took a grinder to the edges of a square-point shovel to make it sharp. Applied the product. Waited 20-30min. Then scraped up the thinset/mess with the shovel and a lot of elbow grease. The point is-- there is a product that will work. It may take a few tries to find it, but something out there does work. Grinding sounds like a LOT of work, a LOT of dust, and less than ideal (FLAT) results.

As to the back-buttering tiles question, I'll take isherwoods' word for it, but I have never seen a Pro that did not back butter tiles. It could be a regional thing?

  • peinal - are you taking about sulfuric acid? Its sometimes used to clean concrete off where it doesn't belong. But whoa, look out. I don't know if I would use it inside. – BrianK Oct 19 at 2:23
  • No. It wasn't sulfuric acid. Perhaps something like this: homedepot.com/p/ZEP-5-Gal-Heavy-Duty-Floor-Stripper-ZULFFS5G/… It has been too long for me to recall. – peinal Oct 21 at 17:49

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