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Old 02-14-2011, 11:10 AM   #1
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Backerboard, tile, tub installl


We are having trouble figuring out how to install the backerboard to the tub - then actually how the tub is istalled, then tile.
I'm attaching a photo of where we are in the process and one of an example of an install. Is the example correct - 0093?
Our tub is porcelain over steel with about 1 inch tall lip - the lip is about 1/16 inch thick.
The backerboard is 1/2 inch, the tile is about 1/4 inch.
Because the backerboard plus the tile would be 3/4 inch, we cannot see how the tub could be attached to the studs and allow the huge overhang of the backerboard and then the tile. It would seem that there should be some furring strips so that the tub sits away from the studs about 1/2 inch so the backerboard would then be flush with the lip - leaving a small space between the top of the lip and the bottom of the backerboard for movement. Then the tile would extend over the lip and be sealed with silicon to the tub.
If this is correct, then how to you secure the tub? Just on the floor? That too is a question - the tub has a piece of non-removeable styrofoam on the bottom, which we have been told to secure to the floor with thinset. How then do you secure the sides of the tub. You cannot drill through the steel so we thought a screw with a washer - but then again, that would cause a bump where the tile would install. Is that the only side secure mechanism, the screws? Shouldn't this tub be attached to some boards underneath somehow?
All of these details are causing a lot of discussion and conflict between us. Can someone clarify all of this?
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Old 02-14-2011, 11:37 AM   #2
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Ok, I'm not an expert, but here's what I did last year.

Id take the tub back out, and start with putting up drywall from floor to ceiling. Then I put the cement board over the drywall (use the moisture resistant drywall, not the normal stuff).

Then, I'd put the tub in....mount it, etc.

Then, when putting up the tile, you're going to use at least 3/16" of mastic behind the tiles....so, put up the mastic right to the top of the tub lip...and even overtop the tub lip....taping off the last 1/8" or so of the tub so you can remove the tape before everything has set.

After the tape has been removed, this will allow for a good surface to caulk to after everything is set

In hindsight, I know there's a moisture barrier that I should have put between the cement board and drywall, but I can't remember the name of it

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Old 02-14-2011, 11:39 AM   #3
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and yea, the bottom photo shows how it should be done
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Old 02-14-2011, 11:48 AM   #4
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thank you for the replies. I am now clear that that tub should not be secured to the studs - because the backerboard should be flush with the top of the tub lip. We really cannot sheetrock the whole wall and then backerboard the whole wall because the bathroom is extremely small - every 1/2 needs to be spared. We have insulated the wall, and there is a vapor barrier on the wall
that being said - how did you secure the tub to the wall? OR is it just secured to the floor?
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Old 02-14-2011, 12:02 PM   #5
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I had a tiny bathroom too, less than 6x6 with a full tub. I secured it to the floor obviously, and screw the lip to the studs behind...of course, the tub I put in was fiberglass, so it was easy to screw through.

In your case, I'd try drill a couple of holes on the top lip and secure it to the wall, but if it's just not feasable, securing it to the floor should be adequate in my opinion.

It's not like there's any tendency of a tub to move, even if it wasn't attached to the floor, I can't see it moving....not a metal one anyway. I'd imagine that's gotta be around 75-100lbs or so, I just can't see it moving
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Old 02-14-2011, 01:42 PM   #6
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Hello my name is George and i work for a Chicago area Home Depot.
Tub needs to rest on the ledger boards and it needs to be attached to the studs with a galvanized roofing nails, don't drilll the lip of the tub just place the roofing nails right above the edge of the lip and the head of the nails will grab on to it.
Further, backer board goes over the lip of the tub and it need to have a 1/4" capillary attraction gap from the surface of the tub.

Furring strips are recommended if installing a backer board over a vapor barrier. Furring strips will create a necessary air gap in between back of the cement board and a vapor barrier.
This same gap will speed out drying of the moisture that gets build up in between back of the CBU and VB.

Last edited by SteelToes; 02-14-2011 at 01:42 PM. Reason: a
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Old 02-14-2011, 05:25 PM   #7
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Holy crap this is utterly amazing to me! All of this advice and most of it dangerous.

Whatever you do don't try to drill that tub lip and never never never try to lap that lip with a nail swinging a hammer that close to the tub. That is an inexpensive steel tub with inexpensive enamel baked on to the surface and it will spall-off huge chunks of enamel if it is impacted or stressed in any way.

Fasten a ledger board to the studs. Gob some construction adhesive on the floor and on the top side of the ledgers. Slide the tub in place and leave it alone until tomorrow.

After the adhesive has had over night to dry you can then get in the tub to fasten the wallboard to the studs. You can do one of two things at the lip. You can back-cut the wallboard slightly so that it will lap the lip or you can stop the wallboard just above the lip and caulk that juncture. The wallboard is now wider than the lip and overhangs the lip slightly. Now you can install the tile so that it covers the gap between the wallboard and the tub rim. The tile is then caulked to the tub.

You WILL NOT have 3/16" of mastic behind the tile that is plain ridiculous. At most using the proper trowel you will only have about 1/6" to 3/32". But listen up !!!! Mastic is the worst adhesive you could use if this tub also has a shower. Modified thinset mortar NOT PREMIXED should be used to install the tile.

The walls have stud cavities for drying if needed but no moisture will get to the stud cavities if a moisture barrier is used over the studs as it should be. Nailing firring over the moisture barrier will only make holes in the moisture barrier, that idea is ludicrous. You won't find that technique in any of the tile industries methods and procedures.

If you were to use a waterproof wallboard such as Denshield you wouldn't need a moisture barrier to begin with and wicking water wouldn't ever be an issue in any area.

You should also verify any and all information you receive on these forums before you jump on to any one's wagon and ride along with their misgivings.

SORRY - I just couldn't witness any more of this insanity without speaking out.
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Old 02-14-2011, 05:40 PM   #8
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Please-----Listen to Bud on this----My advice is the same---Mike---
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Old 02-14-2011, 05:49 PM   #9
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You need to waterproof behind the tile and not rely on your vapour barrier.

Quote:
Originally Posted by angus242

ANOTHER prime example of why how things used to be done are no longer valid when it comes to building showers.



A 25 year old shower that is beyond destroyed. Oh wait, there's a vapor barrier back there, right? Yes, there is. Did it do any good for this situation? Hell no!

Folks, there is absolutely no reason to allow water to get to the substrate and then deal with it, when there are multiple ways to waterproof these wet locations.


Last edited by fungku; 02-14-2011 at 05:54 PM.
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Old 02-14-2011, 07:43 PM   #10
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Here we go...
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Old 02-14-2011, 08:05 PM   #11
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That drawing shows the backer overlapping the flange----That would lead to a curved bottom to the backer

Bottom row of tile would hump out--what would that look like as the tile and caps continue along the tub--down to the floor?.

Works in that drawing--would be an installation failure in the real world.
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Old 02-14-2011, 08:30 PM   #12
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Take the tub and put it on level ground. Measure from the ground to the underside of the lip.

Mount a 2x4 and have the top lip of it at the height you measured (make sure its level!!!)

Put the tub in and secure it by screwing right into the suds directly above the lip of the tub (so that the screw head holds the tub in place, stainless or brass screws work best for this)

Once you've tiled, use bathroom grade caulking around the tub.
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Old 02-14-2011, 09:14 PM   #13
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Wow this thread is all over the place...
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Old 02-14-2011, 09:23 PM   #14
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Here's the last tub I tiled around. Ledger on the wall, backerboard, tub, kerdi, overlapping lip and sealing the bottom with kerdi-fix, then tile.

This way there it comes in very slightly at the bottom, but because I was tiling with ungauged slate and the cedar 2x around the edge you would never notice. In a different situation you could rasp out the bottom of the cbu a little so the lip is flush.

This installation is waterproof.





thinset (w/ kerdi-fix at the bottom)



Last edited by fungku; 02-14-2011 at 09:53 PM.
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Old 02-15-2011, 09:00 AM   #15
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Backerboard, tile, tub installl



The walls have stud cavities for drying if needed but no moisture will get to the stud cavities if a moisture barrier is used over the studs as it should be. Nailing firring over the moisture barrier will only make holes in the moisture barrier, that idea is ludicrous. You won't find that technique in any of the tile industries methods and procedures.


Tiled showers on exterior walls are bound to suffer from moisture problems. One way to reduce moisture penetration into the wall is to isolate the tiled wall from the actual exterior wall with an air space. This prevents water from moving in through capillary action, and instead provides a space into which the tiles can dry out. Vapor from the drying tiles can get back into the bathroom by diffusing through the tile grout or through the paint at the top of the wall. The entire bathroom wall must have an air space.




If you were to use a waterproof wallboard such as Denshield you wouldn't need a moisture barrier to begin with and wicking water wouldn't ever be an issue in any area.

Georgia Pacific a manufacturer of DensShield recommends to leave a 1/8" gap between DensShield and the tub deck.
Please see attached link:

http://www.gp.com/build/product.aspx?pid=4684
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