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Unread 06-12-2009, 08:43 AM   #1
rocknroj
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Roger's Bathroom Remodel

I am replacing my bath floor on a mid '20's home. Down to the original subfloor which is 3/4 lapped boards placed slightly diagonally over 2 x 8, 16" oc.

There is a significant height difference across the 5 1/2' width of the room with the one side as much as 3/4 inch lower than the other side. Most of the slope is in last 16" next to the outer wall, so the outer wall is higher where as the rest of the room settled.

The rough in is done, so tearing up and jacking are out of the question.

After lots of time scratching my head and on my knees with my level, I arrived at a plan and am looking for some feedback.

I will install some 3/4" and 1/2" ply screwed to the old subfloor to stiffen and help level. The outer 12" or so of the room won't get anything. Then I will apply a leveling layer using a cement based product (polymer modified mortar) and work it to attempt to get a level floor. What I will be left with is a mix of exposed ply and concrete mortar.

On top of this layer goes the thinset and then the tiles. Height is an issue as the build up layer brings the floor to the level of the outside floor, so I want to avoid the hardibacker or equivalent.

Questions..

What type of thinset (polymer modified?) The substrate will be cement/mortar) and plywood.

Can/should I install some kind of moisture barrier in the process? The nobel Seal sheet looks pretty good, though aquisition could be tough.

I was going to place `15lb felt between the old subfloor and the new ply but read about a 'vapor sandwhich' so I am leaning against that idea.

Below the bath is finished space so I want to protect against any leaks.

I heard about the paint on stuff like redguard but wonder about its effectiveness. Mostly I shop at Lowes and Home Depot so if you know a product that is readily available at one of these places that would be great.

Still down to the old subfloor, so any advise would be appreciated before I start something that I have to undo.. Thanks.
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Unread 06-12-2009, 08:55 AM   #2
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I don't think that your plan will work. The 12 inches of the exposed plank subfloor is not a suitable starting point for any kind of tile installation except for a floating mud bed. You don't have room for that. Instead, cover the entire area with 1/2" plywood, followed by 1/4" backerboard, then level the floor using SLC or deck mud bonded to the backerboard. Deal with height transitions at the doorway with a tapered transition strip.

Don't compromise your tile installation in trying to get a level transition at the adjoining rooms.

You can waterproof the floor if you want, but remember to seal the wall-to floor joints and any penetrations through the waterproof layer, and build a curb at the doorway, and add a floor drain. After you consider doing all this, you realize that your tile floor will protect your ceiling from all but the most catastrophic flood.
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Unread 06-12-2009, 09:01 AM   #3
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Another option (if you are up for additional work, and really concerned about the final height) is to remove the diagonal boards completely and provide a flat (doesn't need to be level) surface for new plywood by sistering nailers to the existing joists. Then you can build a flat sturdy subfloor without any need for slc or other cement-based leveling approaches.
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Unread 06-12-2009, 10:43 AM   #4
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Thanks for the prompt feedback.. I will go an re-measure. It appears that the typical tile I am looking at is just over 1/4 inch thick.. With the thinset, how much total height increase can I expect? And what would be an acceptable transition height? I was hoping for no more than 1/4"

That outer 12" that would only get a thin tapered layer of mortar under my old plan is pretty stiff (1 rim joist, then a second joist about 8" from the wall and doesn't get walked on.

Do you think if I cover part of the room with 1/2" ply and the other part with 3/4 or 5/8", then level with some mortar, let it cure, then apply the thinset and tile it would be ok? Once again, part of the floor would be plywood and parts would have mortar on them. Is there a problem with tile on plywood, or mortar on plywood followed by thinset and tile? Is it adhesion or water penetration.

Using 3/8" thickness for tile and thinset and 3/4" for ply and backer, + leveling, I would end up with 1" transition between rooms which I think is too much. That's why I came up with the funky idea.

Any specific mortar brand that I can pour out and then scrap away imperfections when partially cured. I used a polymer modified mortar that worked for that, but at $30/bag an alternative from home depot or lowes would be good.

Once again thanks in advance for your advice.
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Unread 06-12-2009, 11:15 AM   #5
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Quote:
Once again, part of the floor would be plywood and parts would have mortar on them. Is there a problem with tile on plywood, or mortar on plywood followed by thinset and tile?
None of this is an approved method for setting tile. There is a reason for that. It doesn't work.

Jal_il"s idea is very good. It will work. Your transition will be what it will be.
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Unread 06-12-2009, 11:57 AM   #6
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Sounds awfully similar to how my bathroom floor was. From your description - it is the outer wall floor joist that is set too high, and so the floor slopes up there?

In my case I decided to remove the subfloor and level the joists. For the outside wall joist that was in fact 3/4" too high, I sistered another joist inside of it at the correct height - and so now the top of the joist is about level with the top of my 3/4" plywood subfloor.

So in your case - if you don't want to remove the subfloor (which might be a good idea to just do) maybe you could cut the subfloor just inside the outer joist and sister another joist to it at the correct height - nail the old subfloor to the new sister joist at the lower height. Just a thought. You will need access to the underside to do this. OR.... cut out the last bay of subfloor and do the same thing with a new plywood section of subfloor.
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Unread 06-12-2009, 04:27 PM   #7
rocknroj
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Thanks for the replies all.

Its too late in the project to remove joists and what not as there is a new bath framed downstairs and all the plumbing is installed.

If I lay the ply, and then a leveling concrete mortar layer could I lay the tile directly on the concrete leveling layer after it has cured ?

Or prehaps a kerdi layer after the leveling mix and then the tile applied to the kerdi.

The leveling compound would be pretty thin on the high side but with the proper primer should stick.

Or maybe I should level as best as possible, nail on a piece of luan and glue some vinyl.

Thanks in advance
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Unread 06-12-2009, 04:35 PM   #8
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As mentioned, to keep the floor height as low as possible, cut out the existing subflooring planks, maybe put on some cleats on the existing joists to create a flat and level set of joists, then put a new subfloor down onto this (some construction adhesive on the joists really helps stiffen things up). This would be level, and fine to start your tiling. To keep the height down, use a membrane like Ditra from www.schluter.com right on the new plywood subflooring. Assuming you use 3/4" subfloor, then add about 1/8" for the Ditra and your tile, the total height might even support a thicker layer of ply to even things up with the other room. If thicker is better, you could use Ditra XL, which is thicker if you couldn't get another layer of ply in there. If you seal the seams on the Ditra, you'll also waterproof the floor. Keep in mind, also mentioned, that if you don't go up the walls and seal around penetrations (like the toilet flange), and at the doorway, a flood will get into the walls and floor anyways.

Note, slc over a plywood subfloor requires lath. It also needs to be thick enough to cover the lath a bit. Many of the brands want 1/2" over the highest point...some can go thinner, and pretty much all of them can be feathered to nothing over concrete slab (which you don't have).
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Unread 06-13-2009, 10:05 AM   #9
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No one is suggesting that you need to remove joists or do anything that would disturb your bath below.

The idea is to remove the plank subfloor, and create a flat surface to attach new plywood. In order to create a flat surface, you may need to sister cleats on to some of the joists that are low.

Removing the subfloor and replacing with plywood will give you a much better result in terms of overall height, flatness, and strength.
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Unread 12-19-2009, 01:02 PM   #10
rocknroj
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Tile adhesive for setting-type joint compound

I am tiling around a tub/shower. The cement board is up and I transitioned between the backer board and the sheetrock with a setting type joint compound (silverset 90) on the advise of a tilesetter I met at the store. I am planning a 2" bullnose trim but it will be attached to the joint compound. Will versabond adhere to this or should I use something else?

Should I put a skim coat of thinset over it first. The bullnose is just ouside the tub and could be extended down to the floor as a leg if I choose to but that would be going over sheetrock (greenboard) which is already primed and painted with semigloss.

I should have extended the backer further but it is rather too late. his is my first tile job..

Thanks in advance.
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Unread 12-19-2009, 01:07 PM   #11
Tool Guy - Kg
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So your drywall to cement board transition will be under the tile. How far does the drywall compound runs under the tile?
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Unread 12-19-2009, 01:12 PM   #12
rocknroj
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I am not sure, getting read to head back over and measure again I believe my 4" tile ends at the backer board and the 2" bullnose would go completely over the silverset.
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Unread 12-19-2009, 01:29 PM   #13
rocknroj
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Is it mastic

This is an update to the original question.. Research indicates that I should use mastic, at least thats what I arrived at looking for an ansi 136.1 standards recommended by usg website. Yet mastic is not good for moisture.. Since the trim is oustide the tub area, getting it to stick to the walls is the main concern I guess.
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Unread 12-19-2009, 04:06 PM   #14
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If the drywall compound is in the wet area, it has to go or be waterproofed. It will melt when it gets wet.

We float our drywall to the CBU all the time. To do this you need to carefully measure where the tile stops. The CBU can stop 1 or 2 inches of where the tile stops, as long as it is outside the wet area. That way the tile bridges over the drywall / cbu joint. Use the same thinset for setting all tiles no matter if they are over the cbu or the drywall.
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Unread 12-19-2009, 04:33 PM   #15
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Like paul said, I'm assuming that your bullnose is past the point where your shower curtain or glass is going. (ie. out of the wet area)

So wipe the compound with a wet sponge and then use thinset. Burn the thinset in first. If you are painting the bathroom then paint the joint first, later score it a little with your trowel, burn thinset and tile.
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