Replacing Tile - Subfloor Questions

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Old 04-03-18, 05:29 AM
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Replacing Tile - Subfloor Questions

Hope someone can answer!

Replacing tile in my bathroom. It is a half bath and not extremely large. The tile is original from construction which was completed in 2002. The tile butts up to the vanity and there is no tile underneath the vanity, only the subfloor. I pulled out the floor register and got a good look at how everything is constructed. Current set up is 3/4" OSB with a 3/4" plywood underlayment for the tile....tile is directly on the plywood with mortar...no cement board under the tile. There are no cracks or damage to the current tile, it is just time to update the look. The transition to the hallway is flat and I am hoping to keep this as flat as possible. What are my best options? My original thought is to try to keep the 3/4" plywood and use Ditra on top of that as an underlayment for the new tile. If the plywood is damaged and needs to be removed, can I use 1/4" plywood over the OSB, then use a 1/4" cement board? All replies are welcome!
 
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Old 04-03-18, 06:28 AM
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I'm willing to bet the plywood was glued and screwed to the subfloor. If that is the case, then there's no way to remove it, unless you cut the entire subfloor out (OSB and plywood). I don't think you want to go to that extreme. If you don't want to add any height, then I think your only option is to remove the old tile, chip away all the old mortar from the plywood (careful not to gouge the plywood), and lay your new tile directly on top of the existing plywood. If you have 1-1/2" of subfloor, then that is pretty solid. Sounds like a messy PITA job, but good thing it isn't a large bathroom.

You'll want to be sure to prep the subfloor properly and use the correct thinset for use on wood (polymer-modified I believe). I'll let the experts take it from here...
 
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Old 04-03-18, 07:41 AM
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Thanks for reply. The plywood is definitely screwed down ( I could see that from the basement) but cannot confirm that it is glued. I am guessing it is. Assuming I can get the plywood in the condition necessary, do you see a reason I would NOT use Ditra over the ply? Just concerned about movement....
 
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Old 04-03-18, 07:44 AM
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1/4" plywood should never exist in a tile subfloor, as it's really flimsy and provides no real structure.

Tiling over plywood is far from ideal and I often advise that floor height is the last thing you should be concerned about when tiling so I would be looking to either remove the plywood and replace with 1/2" ply and 1/4" cement board or just add Ditra to your current structure.
 
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Old 04-03-18, 08:55 AM
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Assuming I can get the plywood in the condition necessary, do you see a reason I would NOT use Ditra over the ply? Just concerned about movement....
Floor height is the only reason I can think of, but that is what thresholds are for. You'll want to get the all of the old thinset off and sand it smooth so the backerboard lays perfectly flat.
 
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Old 04-03-18, 05:18 PM
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Never tile directly to wood, always have a bonding decoupling membrane be it ditra or cement backer both set in mortar. I've said it many times, the tile installation has nothing to do with the height of the adjoining rooms. It needs flat and solid and the correct layers of materials in advance of the tile. Virtually every bathroom out there with tile has a small step up to accommodate for this. Use a marble threshold, they come in thin and thick pieces.n But approaching tile from an height concern is always a recipe for failure.
 
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