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Discussion Starter · #1 ·
Thanks for all the help on this forum.

My plan today is to prepare the bathroom floor for tile by putting down thinset and 1/4 hardibacker on the subfloor. The house is 80yrs old and the subfloor is made primarily with 1" tongue and groove planks with a couple of patched boards. The subfloor is far from completely flat. Some planks sit lower or higher than the adjacent plank (around 1/4" in some places), there are a few quarter inch seams etc. But, I am trying to stay away from replacing the subfloor (The 1" tongue and groove seems amazingly sturdy).

The old floor seemed fairly flat before I removed it and it was a thin sheet of plywood (maybe 1/8") with vinyl. I'm thinking that adding thinset and 1/4 hardibacker will only make the floor more solid and even than it was before.

My question is how much uneveness in the floor can the thinset and hardibacker tolerate/correct. I'm concerned that forcing the screws down flush in the the low spots may bend the hardibacke and squeeze out the mortar underneath? Are there any tricks to this (eg. making the mortar thick, or screwing everything down fairly even, but waiting a few hours to come back to tighten the screws down flush)

Thanks
 

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You left out a step----Add some 1/2" or thicker plywood on top of the 1x sheeting---that 1x stuff moves to much to trust---it will cause tile cracking without a layer of plywood.

Next step is the backer board---1/4" is fine--the backer is not adding any structural strength so thin is fine.

I don't like Hardi Board--especially on a roller coaster floor---here's why. It to stiff and tends to leave more hollow spot--voids--that might not be filled with thinset.

I've seen it actually see Hardi pull out nails,(often roofing nails are used to install backer onto floors.

I prefer wonderboard or Durrock.

----Mike----
 

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Pro Flooring Installer
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For tile you need two layers of subfloor. 1/2" inch or thicker plywood on top of the 1" subfloor.
 

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Discussion Starter · #5 · (Edited)
If I put 1/2" plywood over the "rollarcoaster floor" there will be lots of void space where the plywood is bridging the subfloor. Should I be concerned about these hollow spaces?

My transition from the bathroom tile to the hallway floor is already 1/4". Is a 3/4" transition normal?

The joist are 16" apart. I thought I read in the John Bridge Tile Forum that 16" joist with 3/4 planks is rigid enough to put thinset and 1/4" hardibacker on. Is this wrong? or maybe I mis read it.
 

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If I put 1/2" plywood over the "rollarcoaster floor" there will be lots of void space where the plywood is bridging the subfloor. Should I be concerned about these hollow spaces?

My transition from the bathroom tile to the hallway floor is already 1/4". Is a 3/4" transition normal?

The joist are 16" apart. I thought I read in the John Bridge Tile Forum that 16" joist with 3/4 planks is rigid enough to put thinset and 1/4" hardibacker on. Is this wrong? or maybe I mis read it.
3/4" plywood is adequate for tile,however 3/4" 1x pine is not---

If your Roller coaster floor is to bad for the 1/2" ply to ride the contours

You may need to 'flatten' the floor by removing the 1x sub floor and sistering in a new joist or two--Pictures would help--How bad is the existing floor?
 

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Tileguy
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Let's start at the beginning.

First, the 1" hardwood flooring must be removed unless it is "the" subfloor. The subfloor is the material directly on the joists. So, what is on the joists?

Jaz
 
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