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Old 04-12-2011, 03:34 PM   #1
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Thinset Over Worn Plywood

I'm putting a new tile floor in the bathroom. I've pryed up two layers of old lineoleum only to find a layer of what I'll call 'tarpaper' about 1/32in thick that's stuck like glue to the plywood decking. All of this probably 40yrs old.

If it had stayed in place over the entire floor I'd have just gone ahead and laid in the 5.5mm 4ply I bought to resurface with a clean base for the tile. But unfortunately some paper in areas seeing little traffic over the years came up with the lineolum so I'm guessing there's too much gap for the 4ply to flex and tiles to start lifting.

The only way I've found to remove the paper is heating with a torch and scraping if off with a chisel. Quite the chore and I'd like to get this done in my lifetime!

The old plywood decking itself seems to be in decent enough shape, it's just got gaps where the paper is still stuck down adjacent to areas that it isn't.

My question : Could I use thin-set to fill the areas over the old plywood to bring it flush with the papered areas, or should I just keep scraping away at the paper until I've removed it all ... hopefully before the end of days! Thanks, Mike


Last edited by Muckaman; 04-12-2011 at 03:36 PM.
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Old 04-12-2011, 08:44 PM   #2
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I don't agree with any of what you're planning to do, with the possible exception of removing the paper.

5.5 mm plywood, (probably luaun), is not appropriate in a tile installation. The minimum you should add is 3/8" where the face grain is no less than "C".

I do not recommend installing tile over any plywood, especially in a bathroom.

After installing the new underlayment you should install a tile backer board or a membrane such as Ditra.



TILE GUY - retired- TROY, MI - Method & Product suitability consulting.

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Muckaman (04-16-2011)
Old 04-13-2011, 04:53 PM   #3
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yeah you're right Jaz ...

... the more I looked in thinset the worse the idea became. But I left a coupla details out of my post that drove me in that direction I'd like your comments on.

First of all sits just off my bedroom and was creatively carved into a space about the same size as a small closet ... toilet, small shower and a custom vanity musta been designed and installed my a liliputian craftsman (circa 1970 I'm told). I think there's maybe one square corner in the BR and the rest are all at odd angles. This image shows almost the entire floor ... probably no more than 20sf total:

The larger greyish area being the remaining 'paper' ... the upper area where 3hrs of torching n scraping have gotten me. As I said there's maybe 1/32in step between the two surfaces and that bugs me 'cause I worry about flex.

Along those lines here's another image with a 'step' problem. The plywood section jutting out from the shower base sits 1/16-3/32in higher than the surrounding floor. The way I see it this is a high-traffic spot stepping in and out of the shower and the new substrate will surely flex:

The floor itself sits almost 5/16th's lower than the slate foyer just outside the door ... this is what drove me to consider the 5.5mm 4ply. Also, in trying to match the height of the finished bath floor with the adjacent slate I was going to go with 'peel and stick' vinyl (measures ~0.80in thk).

Called a buddy of mine earlier looking for ideas how to deal with the step from the shower ply to the floor ply. He's gonna bring over some cedar shakes to play with figuring since these taper down to almost nothing they might glue down and give a decent transition to take the step out of play.

Anyway Jaz that's pretty much the rest of the story and where my thinking's at today. Whaddya think? Thanks much for the frank assessment ... now let er rip again. Mucka
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