Can we skip thinset under hardibacker? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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04-10-2006, 11:18 AM
A friend is helping us install a small (50 sq ft) slate tile floor in a bathroom. He cut and screwed down all the hardibacker with no thinset under the hardibacker and no 1/8" joints where the harbibacker seams meet. The floor underneath is plywood, at least 1.5 inches of it. It's very sturdy.

I showed him in the Tile Your World book where it says you CAN'T skip the thin set step under the CBU! He claims he's been installing tile for 15 years and has never had a problem. What are the consequences of going forward with this slate tile job as is, without the thinset under the hardibacker and without joints at the hardibacker seams? I'm pretty nervous about it. Any advice would be great. Thanks!

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04-10-2006, 11:22 AM
Lisa, you are correct and your tilesetter is wrong! You do need the thinset under the backerboard, you do need the 1/8" gaps between the sheets (and 1/4" around the perimeter) and you do need the tape and thinset on the seams. If your tilesetter refuses to correct his mistakes, ask him to leave, and be firm.

Those mistakes account for the majority of tile failures that are discussed on this forum.

Brian in San Diego
04-10-2006, 11:26 AM

Before I knew any better I installed cbu In a bathroom without thinset underneath and what I have now is a popping sound on a small area in front of the tub. Every time I step on that spot the floor groans. No damage to the grout, but it is annoying. If it were mine to do over again, I would definitely put thinset under the cbu and keep the proper spacing.


04-10-2006, 11:39 AM
You need to put thinset down per JH instructions.

He hasn't had a problem, that he knows of. Following instructions so install is waranteed is a good idea. I know floors I have worked on have never been perfectly flat, so the thinset has always been needed. Let the pros weigh in, but they might recommend unscrewing and doing correctly. That's what I would do.

04-10-2006, 11:49 AM
I appreciate everyone's responses. THANK YOU! I definitely want to unscrew it and put down some thinset under that hardibacker and reposition it so there are 1/8 inch joints! I've never done a tile job so I was really hoping to get some responses I could show to my friend (with all his years of experience) so he realizes why I'm insisting on the thinset under the hardibacker. I don't want to lose his friendship and he's been extremely generous to work on our bathroom. It needs to be done right or, in my opinion, it's not even worth doing.

I would still appreciate other posts so I can convince my friend this is the right thing to do. Thank you everyone. Perhaps my bathroom floor (and friendship) will be saved.


04-10-2006, 12:12 PM
If your friend is a man, just tell him to not be stubborn and learn something new today and get over it. Us dopey men let pride get in our way, but the good ones learn to swallow it and get on with life.

04-10-2006, 12:24 PM
Just take a look at the manufacturer's instructions that Gregg conveniently linked to in a previous post. The "I've been doing it this way for xx number of years" excuse is the most overused pathetic excuse in existence. Anyone that uses that excuse would be shown the door if it were me. No telling what else they've been doing wrong for all those years!

04-10-2006, 01:59 PM

As far as tile is concerned, the average lifespan of the average guarantee is pretty short term when you compare it to how long the tile floor or wall is going to last. Just to carry that thought farther forward, the average installer is not likely to call people back after 5 or 10 years and ask to come over to look for hair line cracks or little cracking noises. Bet your friend doesn't do that and won't want to if you asked him to.

So this helps explain why many installers can say sincerely that they have never had a problem.

Add to this, the fact that the average homeowner may not even notice most hair line cracks. And they have no idea who to call. And they don't even know what method was used to make the tile-ready substrate under the floor. And so on...

When an installation is said to have failed, sometimes it still looks OK to the average homeowner. A hair line crack may not be very noticeable. However, many failures are much worse than that, so don't base any conclusion on my using that term in the above paragraphs.

Hope this helps you manage your friend.

04-10-2006, 06:46 PM
Lisa, 1 1/2 inches of plywood is good but doesn't mean you should eliminate the thinset. The thinset fills small voids between the backerboard and plywood. It won't be all that much work to backout the screws and slap some thinset under there. It's worth it. :)

04-11-2006, 11:53 AM
Another question: do you think it makes a difference if drywall is installed first, or tile? We have the option to do either first.

I sure appreciate everyone's replies about the thinset. My boyfriend and I are going to take up the hardibacker and apply thinset. When our friend comes back to lay the tile we'll just tell him what we did, and tell him that while his help is greatly appreciated, we can't afford to cut out important steps in the installation. We are also going to draw a layout for him to use. This is another step he didn't want to do although he's planning a rather complicated layout with a border and already made a few cuts!

04-11-2006, 01:16 PM
Do all your drywall work first. Drywall dust will be very difficult to get out of your grout.

Draw your tile guy a picher of what you want, but don't mark up the floor, let him do that.