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schorsch 08-30-2012 09:21 AM

Installing new sub floor
Looking for some advice.
I just finished ripping out my old floor down to the joists (16" OC). I want to install tile floor and the old subfloor was sub-standard. I am thinking 3/4 Advantech (or should I use 3/4 inch T&G ply?) as a subfloor, then a 1/4 inch hardibacker board. Is this okay?

joecaption 08-30-2012 09:26 AM

Advantec with constrution adhesive on the joist.
How wide are the joist and what's the spans?

schorsch 08-30-2012 09:32 AM

joists are 2x8 and span about 10 feet.

I am also confused about unmodified vs. modified thinset. What should be used UNDER the hardibacker?

joecaption 08-30-2012 09:38 AM

If it was mine since you only have 2 X 8 joist I would go over the Advantec with at least 3/8, 1/2 would be better A/C subfloor rated plywood, making sure to not have the seams line up with the seams in the subflooring and no glue.
It needs to be nailed every 4" on the edges and every 6 to 8" in the field.

I just like to play it safe, not fun doing all that work and have the grout keep failing.

Check all the floor joist to see if there all even before laying the subfloor.
Just pulling a piece of brick string tight or using a 6' level will work.
It does not need to be level, it needs to be flat.

JetSwet 08-30-2012 10:47 AM

Joes right to go over advantech with 1/2" a/c over lap seams of the advantech. Backer holds no subfloor support so you will need the inch or more of ply.
Use modified thinset for cbu & tile

What size tile & trowel size you planing to go with?

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