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-   -   Plywood subfloor seam meets hardibacker seam (30 inches). (

tsayles 09-03-2012 03:30 PM

Plywood subfloor seam meets hardibacker seam (30 inches).
Remodelling small bathroom and took subfloor down to 3/4 planks that were installed on a 45 degree angle. Then installed 3/4 ext. grade plywood with 3" screws and construction adhesive. On top of that I installed 1/4 inch Hardibacker on top of a 1/4 inch modified mortor base and screwed it down with 1 1/4 backer screws. All went fine and I staggered all hardi joints with those in the plywood except in one spot. Where I had to cut out for the toilet flange I used two pieces of plywood to work around the drain pipe. I did the same exact thing for the hardibacker. The floor is solid as a rock and I did leave 1/8 to 1/4 around perimeter of room and between plywood and hardibacker. I plan to tape and mortar the seams with fiber mesh. I am a little concerned about the one seam where I did not stager the joints. I would appreciate any suggestions from personal experience. What are the chances of this causing cracks in tile or grout?

DannyT 09-03-2012 06:12 PM

you shouldn't have any trouble because of that. a lot of people tape the joints as they lay the tile.

the construction adhesive wasn't needed or recommended because it can cause voids under the plywood

which could allow it to flex unless you spread it out with a trowel.

1-1/2 screws were all you needed and you only wanted to screw to the planks and not the floor joists.

tsayles 09-03-2012 06:19 PM

Plywood subfloor seam meets hardibacker seam (30 inches).
Thanks Danny...

I did screw the 3/4 inch plywood into the joists (treated as if the planks were not even there. The 1/4 inch hardibacker was screwed to the plywood only. I guess I did make a few mistakes...anything worth redoing at this time in your opinion?

Yes I plan to have all seams tapes when the tile is set. Do I need to tape the seams under the bathtub?

notmrjohn 09-03-2012 09:58 PM

When do the other bathroom you can make the cut in the hardi at right angles to one in plywood.

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