Backerboard layout question [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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03-14-2009, 10:36 AM
Hi everyone,

I've been told that this is the place to go for the real scoop on how to tile, so here I am. Thanks for any help on these questions.

This afternoon some friends and I are staging a "remodeling intervention" for another friend who's in the middle of a disastrous DIY project. One of the jobs is tiling a bathroom. The area is by the vanity, about 7 feet by 3.5 feet.

The floor is very solid- 3/4" ply subfloor + Advantech. The joists run the long way.

The question is how to install the 1/4" Hardibacker. The pro who started the job put the first piece perpendicular to the joists at the end of the 7 foot run (which is where the door to the toilet is located). This piece is not screwed down so we have flexibility here.

We were planning to go with this and put another piece next to the first one. But this leaves us with 1 foot at the bathroom door entrance (I hope this makes sense--each panel being 3' wide).

That puts the seam between the panels right about where you'd step into the bathroom. Does this matter? Is there more likelihood of cracking if we do it this way?

Maybe it's better to cut the boards, and do something like 2' + 2' + 3'? We're just trying to learn the best way to do this.

Also (sorry this is so long), is it better to undercut the jambs and slide both the backerboard and the tile underneath?

Thank you very much.

Keith in Emeryville, CA-- a little city sandwiched between Oakland and Berkeley.

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03-14-2009, 10:49 AM
Hi Keith,

The location of the seam shouldn't matter as long as you are setting the Hardi in the proper thinset. Make sure your fasteners are into the plywood and not into the joists. I would undercut the jambs allowing enough height for thinset, hardi, more thinset and tile.

03-14-2009, 10:54 AM
where I place my seams never matters to me since I'm taping the joints and also bedding the cement board in thinset then nailing/screwing it in.

Dave Taylor
03-14-2009, 10:54 AM
Thank you for visiting Tile Your World Forums.

The backer-board layout you choose on the bath floor may be just about any way the backer-board will fit.

Be sure, however, to follow THESE ( instructions closely:

In general...... use approved fasteners.... apply thinset between the floor and the CBU.... imbed alkali resistant tape with thinset over CBU adjoining edges.... leave 1/8" space between CBU sheets and 1/4" space between walls and other immovable objects and CBU..... and do not align four CBU corners..... or lay CBU so that it's edges line up with subfloor or underlayment edges.

As far as undercutting door frames by including room for both tile and CBU....
sounds like a solid plan to me.

Hope this helps.

EDIT:.... Well.... I see that both Brian and Eric done beat me to the answers.
It's hell to git's old and slow :---)

03-14-2009, 11:01 AM
Hi Oldrem,

Thanks for the reply and suggestions. It's always great to learn from folks with experience.

03-14-2009, 11:03 AM
Brian and Dave,

I appreciate the feedback and additional information. I think all systems are go! Thank you so much.

03-14-2009, 11:05 AM

Thanks also for the warm welcome and link to the Hardie site.

03-14-2009, 11:14 AM
I know it's a lot more work, but have you all considered removing the doorway framing, and rebuilding it on top of the tile once it is finished for a "looks like the original floor" look?

03-17-2009, 01:38 PM
It's a little extra work but I've always undercut in a rough pass just enough for the CBU to fit under with no problems. After that, I lay a small sliver of tile next to the casing/jam on top on another 1/16" spacer and lay my backsaw blade on top. It makes a perfect cut with the right spacing to allow the tile and thinset to bring it flush.