Prepping wood floor for bathroom floor tile.

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  #1  
Old 08-12-11, 07:17 AM
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Prepping wood floor for bathroom floor tile.

Long story short is that made a poor decision on hiring someone whose credentials I didn't check, and now my bathroom remod is partially done. I need to correct several mistakes in the plumbing and wall tile prep for sure, but I may be OK with the floor tile prep. As to the floor tile prep:

The bathroom is 5' wide as you enter it and 7' deep. With a bathtub at the far end, this leaves a floor area of 5' x 4.5'. The subfloor is a combination of hardwood and plywood (the plywood apparently replaced the rotted areas). All that's been done at this point is that 1/2" Hardibacker has been laid and attached to the subfloor with the Hardiback screws. There is a 1/8" gap between the two Hardibacker panels on the floor. Here are my questions:

Should some sort of waterproof membrane be put down under the Hardibacker, or should I leave it be?

If no membrane is needed, should there be adhesive beneath the Hardibacker to attach it firmly to the subfloor to avoid creaks/squeaks?

I believe that I should put thinset between the two panels and tape with fiberglass tape before I put down tile right?

Is there anything else I should do to prep the surface before I start laying down thinset and tile?

Thanks in advance!
 
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  #2  
Old 08-12-11, 11:10 AM
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As a DIYer and not a tile expert by any means, but I have laid my share of tile, I believe the recommendeded method to install backer board is to apply thinset first and then screw it down. In addition it sounds like you may still not have enough support on the floor if you only have plywood and some hardwood strips under the backer board. Hardi board doesn't really provide that for you either. A good alternative solution could be to remove the hardi board and install a product like Ditra over the subfloor. This would both provide you the waterproof membrane you should have in a bathroom and also provide you with the floor strength you need to avoid tile movement and still not further build up your floor height. That is what it is designed to do anyway.
 
  #3  
Old 08-12-11, 08:35 PM
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The subfloor is a combination of hardwood and plywood (the plywood apparently replaced the rotted areas).
Are you sure about that? Hardwood is not generally used as THE subfloor. How old is the house? Is there a crawl space or a basement under there?

All that's been done at this point is that 1/2" Hardibacker has been laid and attached to the subfloor with the Hardiback screws.
If there is no thin set mortar under the Hardie it was not done right.

Should some sort of waterproof membrane be put down under the Hardibacker, or should I leave it be?
No, just thin set mortar.

If no membrane is needed, should there be adhesive beneath the Hardibacker to attach it firmly to the subfloor to avoid creaks/squeaks?
There you go, but not for exactly for those reason. The thin set provides full support the the boards. The thin set hold it up, while the fasteners hold it down.

I believe that I should put thinset between the two panels and tape with fiberglass tape before I put down tile right?
Absolutely.

Give us the answer to the first point about the subfloor above.

Jaz
 
  #4  
Old 08-13-11, 04:31 PM
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Other issues too.

The house is 95 to 100 years old, give or take 5 years. I'm in a Pasadena, California. Most of the house still has the original hardwood floor. There is a crawlspace underneath. I probably used the wrong term...when I wrote "subfloor" I was referring the surface that the hardibacker was resting on. In this case that would a floor that's a patchwork of the original hardwood strips and partially damaged plywood. I assumed that the "contractor" would have repaired the voids in the original floor, but at this point I doubt it. I'll likely have to put in some floor leveling compound on the wood.

Also, I'm looking at the state of the floor right now, and it looks like the "contractor" put up some new greenboard wall over the edge of the hardibacker floor. This means that I'll have to tear out much of the new greenboard just to pop out the hardibacker on the floor. I've never worked with wallboard/drywall before, so I have yet another thing to figure out. Crap.

So in some places, the greenboard wall runs down to the subfloor and the hardiboard floor butts up against it. In other places, the hardibacker floor runs a half-inch underneath the greenboard wall. I really don't want to mess with the greenboard walls, since the "contractor" actually did a decent job taping and prepping the walls for painting. Can I just score hardiboard with a carbide blade where it meets the greenboard and break off the edge with a chisel so I can pop the hardiboard floor up without disturbing the greenboard walls...or is this a really bad idea?
 

Last edited by NoMSG; 08-13-11 at 05:02 PM.
  #5  
Old 08-13-11, 06:07 PM
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I still don't know what the subfloor is made of.

When you have hardwood over a subfloor, the hardwood needs to be removed and plywood installed. In an old house such as your, the subfloor will not be plywood, you'll find planks. You need to look from below. So, any plywood you see is most likely an underlayment installed over the subfloor planks.

If there is no thin set under the Hardie, it'll come up easily. In your case I might be tempted to continue and just leave the hardwood/plywood combo and hope for the best. It'll be a pain to remove the hardwood and old ply and install new ply then reinstall the Hardie. It's wrong, but it should still work OK. All this is dependent on a smooth flat structurally sound substrate.

So, to summarize, remove the Hardie, spread thin set mortar with 1/4x1/4" trowel, set Hardie with screws, then thin set & mesh tape all seams.

Jaz
 
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Old 08-14-11, 04:02 AM
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Jaz, I think that long ago, the hardwood was laid directly on joisting. I remember my grandparent's house. It had hardwood, but snow would blow up in the winter through the cracks that opened up with cooler weather. You would wake up under your 6 quilts (that weighed 100#!) with snow on top of your nose .
 
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Old 08-14-11, 06:11 AM
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I grew up in a stone farmhouse built in 1840. It had true 1 X 8" oak boards for the floor. The bays between the joists in the cellar were covered with tarpaper to block drafts. I have fond memories of 100# quilts in my unheated bedroom.

NoMSG - I'm not a tile guy but I have two rooms in my house that I tiled over 1/4" Hardibacker where I did not use thinset to bond to backer board. I have not had a single problem with the tile job. For a bathroom as small as yours I would not sweat it. If the floor is stiff enough you will be fine.

I do have a question for the tile guys though - I have been told that tile should not be laid directly on plywood because the plywood sucks water from the thinset inmpacting it's cure. If that is correct wouldn't a wooden subfloor suck water from thinset used to bed cbu?
 
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Old 08-14-11, 08:26 AM
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Thanks for the reply.

Any suggestions on whether I should chip off the lip of the Hardie with a blade and chisel to get it out from under the drywall that was laid over two opposing edges (the other two edges butt against another Hardie panel and the bathtub)? Or should I just bit the bullet and partially take out the drywall so I can pull the Hardie up?
 
  #9  
Old 08-14-11, 08:35 AM
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Originally Posted by Wayne Mitchell View Post
NoMSG - I'm not a tile guy but I have two rooms in my house that I tiled over 1/4" Hardibacker where I did not use thinset to bond to backer board. I have not had a single problem with the tile job. For a bathroom as small as yours I would not sweat it. If the floor is stiff enough you will be fine.
That's reassuring. Normally, I'd be fine with pulling the Hardie and putting thinset under it. But I'm not sure if it's worth taking out part of a wall or two to do it. I'm also concerned because I doubt that the "contractor" leveled the floor underneath it. On the other hand, he used 1/2" Hardie, so it's a bit stronger than the 1/4". Maybe I should jump up and down on the boards to see what happens.
 
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Old 08-14-11, 09:53 AM
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The more I read, the more I get confused. Are you replacing cbu on a wall or floor? Or both? I don't understand "taking our part of a wall". No need to thinset the 1/2" cbu on the walls. Only the 1/4" you use on the flooring. Adding to the thickness of the cbu will not give strength to the flooring. If you bounce on it and it moves, it will move with the cbu fastened to it. Fix the floor first.
I doubt the cbu was fastened directly under the sheetrock. Removing all the screws should allow you to pull the cbu from under the edge of the wall sheetrock.
 
  #11  
Old 08-14-11, 05:43 PM
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Chandler - If I understand the OP correctly he is cleaning up an unfinished install left behind by a bolted contractor. He has 1/2" CBU on the floor over a mix of plywood and hardwood in a small bath. His contractor did not bed the CBU in thinset he simply scrrewed it down to the subfloor. The OP is concerned that if he must pull up the CBU in order to bed it he will have to cut away some drywall that extends over the edge of the CBU.

My suggestion was that in such a small space I don't think he will have a problem and I think he should just go ahead and lay the tile. Of course that's assuming the floor is providing adequate support.
 
  #12  
Old 08-20-11, 06:51 AM
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Chandler:

Sorry for the confusion. Wayne's understanding is 100 percent accurate. The only reason I may have to take out the wall is because it (the wall) was layed over the edges of the cbu. I can't pull up the cbu without either breaking off the edge that's under the walls or taking out part of the wall.

Originally Posted by Wayne Mitchell View Post
Chandler - If I understand the OP correctly he is cleaning up an unfinished install left behind by a bolted contractor. He has 1/2" CBU on the floor over a mix of plywood and hardwood in a small bath. His contractor did not bed the CBU in thinset he simply scrrewed it down to the subfloor. The OP is concerned that if he must pull up the CBU in order to bed it he will have to cut away some drywall that extends over the edge of the CBU.

My suggestion was that in such a small space I don't think he will have a problem and I think he should just go ahead and lay the tile. Of course that's assuming the floor is providing adequate support.
 
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Old 08-20-11, 12:24 PM
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Why? There are no screws in that 1/2" of cbu. If you remove all the screws, that tab of cbu should pull out from under the vertical cbu on the wall. New cbu can be installed to or under the old wall.
 
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Old 08-24-11, 12:03 AM
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Originally Posted by chandler View Post
Why? There are no screws in that 1/2" of cbu. If you remove all the screws, that tab of cbu should pull out from under the vertical cbu on the wall. New cbu can be installed to or under the old wall.
Here's the layout: One sheet of cbu has the tub on the north side and another sheet of cbu on the south side; but about an inch of the east and west edges are under the drywall...I can't get the cbu out intact without tearing out part of the east or west wall. Same basic situation for the remaining cbu sheet on the floor.

At this point, I think I'll go ghetto and just screw down the cbu sheets and check how solid and level it is. If it's good enough, I think I'll just lay down the tile.

Thanks everyone!
 
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Old 08-24-11, 03:49 AM
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OK, I'll try again. You are saying the cbu is in a solid sheet and extends under the sheetrock? Why not cut the cbu down the middle, unscrew it and pull the two halves out, each from under the sheetrock? Of course pictures would clear up this spiderweb mind a little, because words can't describe what you have, and we can't see what you see.
 
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Old 08-24-11, 06:04 AM
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Cutting the CBU in place could be a semi PITA. I'm not sure of the consequences of not bedding the backerboard in thinset, but I'm sure that in a 5 X 7 space it wouldn't be too catastrophic.
 
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