Somewhat uneven floor in a bathroom

I ripped out the tile flooring and part of the sub flooring in our bathroom, since the tile was all cracked and part of the sub floor was somewhat rotted. The order of flooring was: 1/2" plywood, 1/2" particle board, then tile. I ripped out all the particle board and tile, plus I cut a rotted 4' x 3' piece of the 1/2" plywood, leaving a 4' X 3' area exposed down to the flooring joist.

I put a straight edge on the exposed joists and saw that they are not even with each other, nor level (they are somewhat close to level and even) . I plan to re-tile the flooring once I have replaced the 4' x 3' plywood section, plus another layer of 1/2" plywood over the entire floor area of the bathroom. I was going to apply Ditra membrane then tile the floor.

My question:

1. Should I shim the sub floor so it is level and even? or
2. Should I just use floor leveler? If you suggest leveler, should I apply it just before the Ditra? or
3. Should I just adjust the uneveness of the floor but adjusting the amount of thinset I use on the tile?

 

So now we know the exposed joists are uneven. What about how straight the rest of the floor is? And how bad is any of this that it actually matters that much?

Probably most houses are not technically flawlesly perfect, either. You are relying on meticulous carpenters who check crowns on every joist when installing them, or who care enough to pick straight ones, or who might think to check that every one is 7 1/4 or 9 1/4 without one every once in a while that is 7 1/2 or 9 1/2 (as I have found). And/or joists can sag over time with the weight above coupled with span length and even humidity differentials between what is above and what is below.

For your question about leveling? From just what you have said so far, I'd personally choose to fix the floor at joist level, as grinding or planing away, or shimming are both fairly easily doable.

 

Of the entire 7'5" x 5' floor surface (including under the tub), only 4' x 3' is exposed down to the joists (I have to replace this area because it was rotten, the piece is cut and ready to screw down). The rest of the floor has a layer of 1/2" plywood nailed down. I am going to put another layer of 1/2" plywood over the all the area (but not under the tub). Should I still try to shim up and level the exposed area and try to raise up the nailed down area?

 

Yes on the exposed area. After all - why not?. Everything else above it then would be solid/no fillers. What exactly is wrong with the nailed down area?

You'd probably do yourself a great service to the longevity of your new tile floor by removing the top 1/2 inch and this time go with cement board. The reason your old floor probably so cracked up was due to the wood material, and probably water got through the grout and into the wood material.

One thing I am puzzled by however is that 1/2 was used for the bottom layer. That is rather odd. Normally 3/4 was used and then 1/2 put on that. You might consider for reasons of deflection to add an additional 1/4 inch ontop. Glue it as well as screw it for additional rigidity. Then put the cement board on the very top of everything. If your tiles butt up to the tub, as opposed to going under the tub, that extra quarter inch may not hurt too much. Even if the tiles DO go under the tub, it should not hurt if they now butt up to the tub, as commonly occurs anyway in remodel projects where tile was an afterthought. You just have to seal the grout and caulk good where tub and tile meet. I'm not sure how height is at your door. But consider this.

 

Yup, I agree with ecmans. Hopefully you are not using 1/2" ply over the joists. It should be at least 5/8" T&G ply over the joists, and if you are installed any type of natural stone, you are going to need another layer, like 1/2".

 

I have 1/2" plywood over the joists, plus another 1/2" layer over that in a perpendicular direction (1" total). Is this ok? It is only a 5' x 5' floor space.

 

It sistered up the joists to level out the cut out 4 x 3 area and this area is now a lot better. Actually after checking the nailed down area more, it is fairly level, so I guess I don't need to worry about it.

I was going to use Ditra membrane over top of my two layers of 1/2" plywood. What I've read, this works out pretty good as a base for ceramic tile. What do you think? check out this link: http://www.youtube.com/watch?v=f6FyWs2WZ1k

Is 1" (2 - 1/2" layers of plywood) ok for tile if I use Ditra?

 

I would seriously think about replacing that 1/2" that's over the joists with at least 5/8" T&G or thicker. If you do that, you can install your Ditra, which is great stuff, then tile.

 

So two 1/2" layers of plywood set perpendicular to each other is not a good base for Ditra and then tile? It sure seems pretty solid when you walk on it.

 

It's still not enough.

Schluter requires at least a 5/8" thick subfloor and I would heed their requirements.

http://www.schluter.com/media/brochu...k-2008-ENG.pdf

 

Maybe I could glue the two layers together... surely this 1" bilayer is as strong or stronger than 5/8" single layer...

 

You might be the best judge. Span has something to do with it, for one thing. And it(the floor) may be stronger also if by an exterior wall. Not all plywood is the same, also. Some has only a few plies, some has 5, for example. You would be right about the glue theory, I'd imagine. Probably the open space in that bathroom, that is outside the tub, is not all that great, which also works in your favor. It is not like this is one of those wide open country kitchens.

You could also have some beefy friend jump up and down on the floor while you see what it does, before making up your mind. Or, hold something heavy in your arms (a kid?, or barbells if you have them) while someone else looks at the floor while you kind of raise up and down (or have them do it while you watch).

 

Your subfloor should be minimum 5/8", but its not. Screwing another layer of 1/2" over the 1/2" you have doesnt solve your problem. Gluing probably doesnt either. There has been testing done on this that says that there are benefits to not using glue.

If you decide to use glue, it has to be a full spread exterior wood glue and you'll need to use lots of screws and work fast before the glue sets up. This wouldnt be my first choice. Dont use beads of construction adhesive, as that will create voids between the two layers and only make it worse.

5/8" tongue and groove plywood is the minimum for a subfloor over 16" oc joists for ceramic tile (tell me you aint usin natural stone). Id skip the glue as it'll likely do more harm than good. Id add minimum 5/8" exterior glue plywood over the 1/2" that you have. Normally a second layer of plywood gets screwed to the first avoiding the joists. Id not do that here as screws will tend to strip out of the 1/2" plywood subfloor. Id screw to the joists as well to make sure that the plywood underlayment is well secured. Yes you will loose some of the uncoupling benefits from screwing the second layer of plywood to the joists but screws stripping out of the 1/2" subfloor wont be an issue.

Then use an isolation membrane or cement board over the two layers of plywood.