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Old 12-28-2008, 04:57 PM   #1
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Installing greenboard around new fiberglass tub


We're remodeling our upstairs bathroom and are replacing the tub. We will not be tiling the walls..will be putting up an acrylic liner around the tub instead.

The old tub was a standard sized 60x30 steel enameled tub with a hairline crack in it. Previous owner "hid" the damage by covering the tub with a 32" wide acrylic liner, so there was a 2" gap between the liner and the tub. The original wall was 4" ceramic tile set on regular drywall (not green board), and one wall looked like it was assembled using odd sized scraps of drywall with cardboard strips stapled to some smaller pieces to hold them together...needless to say it was mush.

There was extensive rot and mold damage, and have removed all the old 1/2" drywall from around the tub and about four feet in front of it on both sides (The water damage extended over three feet from the tub, and under the commode). I've cleaned and replaced all the affected lumber in the walls and floor and have re-insulated, and dry-fit the new tub. I will be installing 1/2" green board, but the 1/4" thick nailing flange on the new fiberglass tub has me concerned.

If I use 1/4" furring strips on the studs around the tub to make the new green board sit flush over the nailing flange...the new walls wont be flush with the existing walls where they'll meet.

If I DON'T use furring strips, the new green board will "bulge" over the nailing flange and will leave a gap behind it.

The bathroom is only as wide as the tub, and don't want to have to remove all of the remaining drywall in the room.

Is there a way to do this that I'm not seeing...?
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Last edited by Mikester; 12-28-2008 at 05:13 PM. Reason: Added image
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Old 12-28-2008, 05:22 PM   #2
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Installing greenboard around new fiberglass tub


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Originally Posted by Mikester View Post
We're remodeling our upstairs bathroom and are replacing the tub. We will not be tiling the walls..will be putting up an acrylic liner around the tub instead.

The old tub was a standard sized 60x30 steel enameled tub with a hairline crack in it. Previous owner "hid" the damage by covering the tub with a 32" wide acrylic liner, so there was a 2" gap between the liner and the tub. The original wall was 4" ceramic tile set on regular drywall (not green board), and one wall looked like it was assembled using odd sized scraps of drywall with cardboard strips stapled to some smaller pieces to hold them together...needless to say it was mush.

There was extensive rot and mold damage, and have removed all the old 1/2" drywall from around the tub and about four feet in front of it on both sides (The water damage extended over three feet from the tub, and under the commode). I've cleaned and replaced all the affected lumber in the walls and floor and have re-insulated, and dry-fit the new tub. I will be installing 1/2" green board, but the 1/4" thick nailing flange on the new fiberglass tub has me concerned.

If I use 1/4" furring strips on the studs around the tub to make the new green board sit flush over the nailing flange...the new walls wont be flush with the existing walls where they'll meet.

If I DON'T use furring strips, the new green board will "bulge" over the nailing flange and will leave a gap behind it.

The bathroom is only as wide as the tub, and don't want to have to remove all of the remaining drywall in the room.

Is there a way to do this that I'm not seeing...?
It appears that the tub is shimmed out already ,is that correct? I would run shims, 1/4" to 0 approx.1' long and the green board will transition there to existing dry wall & mud

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Old 12-28-2008, 05:33 PM   #3
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Installing greenboard around new fiberglass tub


I would advice against using greenboard at all. For the extra $15 or so overall, get GP's Densarmor. It's a paperless drywall so no chance of it growing mold.
This picture of a bathroom I recently remodeled had one of those fiberglass surrounds over it. Neither greenboard nor the fiberglass stopped the mold:
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Old 12-28-2008, 05:37 PM   #4
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Installing greenboard around new fiberglass tub


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I would advice against using greenboard at all. For the extra $15 or so overall, get GP's Densarmor. It's a paperless drywall so no chance of it growing mold.
This picture of a bathroom I recently remodeled had one of those fiberglass surrounds over it. Neither greenboard nor the fiberglass stopped the mold:
would it be safe to assume, perhaps it wasn't done correctly? lol......
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Old 12-29-2008, 12:25 AM   #5
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Installing greenboard around new fiberglass tub


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Originally Posted by butlersprints View Post
It appears that the tub is shimmed out already ,is that correct? I would run shims, 1/4" to 0 approx.1' long and the green board will transition there to existing dry wall & mud
Yes, There are shims in place - though they aren't set and the tub has not been screwed into the studs yet. I thought about running longer shims up the studs like you proposed..I figured that would create a barely noticeable gentle taper going up the wall, but those wouldn't address the difference going horizontally.

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Originally Posted by angus242 View Post
I would advice against using greenboard at all. For the extra $15 or so overall, get GP's Densarmor. It's a paperless drywall so no chance of it growing mold.
I checked into using paperless, and quite honestly was turned off by how weak and brittle it seemed, almost every single sheet in stock at the Menards and Home Depot by me was crumbling in at least one spot.

Either way, cementboard, greenboard, or paperless drywall, I will still be running in to the same problem with the nailing flange causing the walls to not be flush.
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Originally Posted by angus242 View Post
This picture of a bathroom I recently remodeled had one of those fiberglass surrounds over it. Neither greenboard nor the fiberglass stopped the mold:
That picture you supplied is pretty fnasty though...obviously the fiberglass surround trapped moisture in...I'm guessing the leak was behind the greenboard to begin with.
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Old 12-29-2008, 09:21 AM   #6
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Installing greenboard around new fiberglass tub


I've run into the same situation. You have two options as I see it. 1) shim the face of all the studs the thickness of the flange or 2) cut a corner out of the back of the drywall to accomodate the flange. I've done that and then smeared the groove full of drywall mud before fastening the drywall. When the mud sets up it will be solid between the drywall and the tub flange. I would definately use fiberglass drywall. The facer may be a little more fragile going up, but it will be a lot tougher than paper if it gets damp.
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Old 12-29-2008, 12:10 PM   #7
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Installing greenboard around new fiberglass tub


I'm with maintenance 6. Those are your 2 choices. Actually, if I were doing the job, I'd use either a cement backer or at least, the paperless wallboard. I just suggested the Densarmor because you specified drywall, not CBU.
So for your case, if you aren't fond of the Densarmor, maybe try Hardi. It will be probably the best choice to be able to notch the bottom edge over the tub lip (if that's the way you decide to go).
As for the Densarmor being and brittle, that's definitely not the case. The moldy pic bathroom I remodeled was spec'd with Densarmor throughout (except for shower area) and there was no problem with it. We even used it on the ceiling. I have 6 sheets sitting in my garage that will be going into my own bathroom remodeling project.
And I refer to the moldy shower picture not to say it was done right or wrong, but just to show that greenboard will NOT stop mold IF there is any kind of moisture penetration. The point is to be better prepared if something goes wrong rather to assume something is 100% sealed only to have a pin hole ruin your entire bathroom.
Good luck!
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Old 12-29-2008, 06:12 PM   #8
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Installing greenboard around new fiberglass tub


Ok, I am going to pick up a small sheet of 1/2" hardiebacker and try to figure out how to notch out a strip about 1" high and 1/4" deep. It sounds to me like the best option so far...you think running it along a table router will work?

If I can do it without cracking the board, then I'll use it instead of the greenboard...this way I'm covered if the wife decides she does want tile after all....
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Old 12-29-2008, 07:51 PM   #9
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Installing greenboard around new fiberglass tub


Not sure if I missed something in the post, but could you not just mount your hardibacker, densearmour, greenboard etc, flush with the top of the tub flange, making the flange and wall all flush? Then the fiberglass surround sits atop the tub rail, making the tub flange your flashing? Looking at the pic, it appears that the edge of the tub flange is about 1/2" from the stud?
Just thinking outloud...
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Old 12-29-2008, 08:33 PM   #10
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Installing greenboard around new fiberglass tub


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Not sure if I missed something in the post, but could you not just mount your hardibacker, densearmour, greenboard etc, flush with the top of the tub flange, making the flange and wall all flush? Then the fiberglass surround sits atop the tub rail, making the tub flange your flashing? Looking at the pic, it appears that the edge of the tub flange is about 1/2" from the stud?
Just thinking outloud...
Brett

You didn't miss anything, and it's not your imagination...the one shim that can be seen in the photo has the largest gap around the tub, the very next stud is right up against the tub and there is no room for a shim. I've been manipulating a 3'x3'x1/2" sheet of foam insulation around on the wall (it's just so much lighter than an 8x4 sheet of greenboard), looking at the outcome of several scenarios. If I did what you suggest, in that spot the wall would slope inwards, and appear flush over the tub, but then would stick out over the top of the flange by about 1/4" around the rest of the tub. I was contemplating doing just that, and then covering the opening left in front of flange and under the greenboard with some setting type joint compound and silicone before covering with the acrylic surround. If I can't make do with hardiebacker, this will probably be my next approach....

... and if that doesn't work...I'm seriously tempted to get rid of the fiberglass tub and get another steel enameled one..without the crack, the molded liner, and the 2 inch thick fungus pile growing in it.
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Old 12-30-2008, 10:55 AM   #11
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Installing greenboard around new fiberglass tub


Your supposed to stop the boards a the top of the tub flange. This prevents the board from wicking water.
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Old 12-30-2008, 06:49 PM   #12
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Installing greenboard around new fiberglass tub


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Your supposed to stop the boards a the top of the tub flange. This prevents the board from wicking water.
You're only the second person I've heard say that, everybody else, including the tub manufacturer says to install the wall material over the nailing flange, covering the screw heads..if using greenboard install edge paper side down.
How would you fill in the space in front of the flange, and under the wallboard?

Last edited by Mikester; 12-30-2008 at 09:09 PM.
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Old 12-30-2008, 06:53 PM   #13
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Installing greenboard around new fiberglass tub


So, I was thinking..if i run 1/4" shims up the length of all exposed studs, and use 1/4" greenboard instead ... that should resolve the situation, right? ideas?
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Old 12-31-2008, 10:31 AM   #14
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Installing greenboard around new fiberglass tub


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covering the screw heads..if using greenboard install edge paper side down.
How would you fill in the space in front of the flange, and under the wallboard?
Are there screws going through the flange? I didn't see that in your photo. Is the screw where I have circled in red? Usually the green board or cement board would sit @ the top of that flange. Then tile would cover the seam between the flange and the wall material.
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Old 01-01-2009, 05:14 PM   #15
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Are there screws going through the flange? I didn't see that in your photo. Is the screw where I have circled in red? Usually the green board or cement board would sit @ the top of that flange. Then tile would cover the seam between the flange and the wall material.


The tub is not screwed in yet, I've only dry-fit it, checking for level, etc..., but yes the screws would be at every stud where you've circled in the pic. And as noted in the original post, I am not tiling, I'll be putting up an acrylic surround. The surround is just a thin glue-on acrylic sheet..not one of those 1.5" thick direct-to-stud wall systems.

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