No thin between plywood floor and hadibacker and other questions

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Old 05-11-06, 09:43 AM
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No thin between plywood floor and hadibacker and other questions

I have 3 questions about tiling a bathroom that was redone from scratch. Let me give some relevant background first. On the floor, there is 3/4" plywood with Hardibacker screwed on top of the ply tightly -- however, there is no thinset between the ply and hardibacker. Between the hardibacker pieces, there are seams that are at least 1/8" wide. The gaps are not filled or taped. I have already taped the undertile heating wire on top of the hardibacker with a special duct tape supplied by the heater manufacturer, after first priming the board. Some of the wire crosses over the hardibacker seams. I plan to use thinset to tile over the heating wire.

Question 1: From reading the threads here, the recommendation is to use thinset between the ply and the hadibacker. If I don't want to undo everything done so far, can I compensate by adding more screws to make it tighter?

Qestion 2: Do I absolutely need to tape the seams of the backer board? It would be tough with the heating wire already installed. Can I just fill the gaps between the hardibacker sheets with thinset as I install the tiles? The floor was leveled before installing the ply subfloor.

Qestion 3: To install the wall tile over green board, it was suggested that I use a ceramic tile adhesive. The brand is AcrylPro. Any opinions on this? Can I use this adhesive also on the ceiling, with 6x6" ceramic tiles? Can I use it also over cement board?

Thanks in advance for the help.
 
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Old 05-11-06, 10:52 AM
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Yes the cement board should have been applied with thinset. Now that it's down I would just roll with it. Since you can't tape the joints now at least try to fill them in. There is supposed to be about 1/8" between them so don't worry about that. The screws should be about every 8", 6" on the edges. If you have that already don't bother adding more screws. Too bad you are going over green board for tile. More imprtant to have cement board on the wall then on the floor IMHO. I guess you can use the premixed on the greenboard but I would thinset on cementboard. Important to use a good thinset. Not the crap they have at home depot. I like Tec Fullflex. Important especially on a partially botched job. Good luck
 
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Old 05-11-06, 12:42 PM
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BuiLDPro68, Thanks.

The wall around the tub and the lower half of the remaining walls is cement board, and I will be using thinset to tile per your suggestion. The half-tiled walls in the bathroom, however, will have green board in the area not tiled. Because the joint between the green board and the cement board will be covered by the top row of tiles, I am not sure whether to use an adhesive for that row of tile, or thinset. Also, should I tape that joint [green-to-cement board]? Should I use thinset or joint compound for taping? What kind of tape is recommended? What kind of tape should I use on any of the floor-board joints that are not covered by the heating coil and can still be taped?

Thanks again.
 
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Old 05-11-06, 09:15 PM
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Use a fiberglass mesh tape and use modified thinset over the tape. They sell a mesh tape made for backerboard, it will hold up better than the regular mesh tape which gets weakened by the alkali in the cement.
Use a wall mastic for the non wet wall areas, dont use the premixed thinset in a bucket for anything.
Keep plenty of spare tile on hand, without thinset under the cement board you may very well experience cracked tile down the road. It would be a good idea to cover your mat in a 1/4" layer of Self Leveling Cement to encapsulate it so when you dig up a broken tile and the thinset, you dont ding the wire and kill the circuit.
 
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Old 05-12-06, 07:30 AM
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You have made a bad mistake here with no thinset under the cement board. This mistake is known to cause many failures, loose cracking grout, cracked tiles. I know it sounds like a lot of work and maybe some wasted money but you remove everything down to the plywood and do it right.

Your spending a lot of money and a lot of your time on this project so why not do it right and know that its going to last. If and when it fails it will be a nightmare, especially with the mats. If you dont want to do this, then do as Tileguybob suggests and
Keep plenty of spare tile on hand, without thinset under the cement board you may very well experience cracked tile down the road.
 
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Old 03-31-07, 06:37 AM
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Although this is an old thread, I just wanted to say thanks for your input. I was debating on whether I really needed to put thinset underneath the backerboard of my floor. The floor is flat as can be, and I am only doing a 5' x 4' entry. Since I am having 3/8" grout lines, after reading this I definitely want to. Thanks!

I wonder how their bathroom floor went?
 
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Old 04-02-07, 07:08 AM
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Well, given that they were also using heated floor cables, without thinset underneath and without taping the joints, I'd say probably down the waste pipe. I'd expect just the movement created by rapid thermal expansion introducted into the assembly over unsupported backerboard to kill it even quicker than just an install over unsupported backer.
 
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Old 04-13-07, 06:28 PM
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does any one have a recommendation for a good quality SLC?

thanks
 
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Old 04-14-07, 09:44 AM
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Originally Posted by christy123 View Post
does any one have a recommendation for a good quality SLC?

thanks
The one sold at HD is fine. Look in the tile section.

Ardex makes a great one if you can find a local supplier. Mer-Krete is also good but not many carry it.
 
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