Author Topic: Can a tub be screwed to green bored or am I screwed ?  (Read 836 times)

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Offline I screwed up

  • Posts: 1
Can a tub be screwed to green bored or am I screwed ?
« on: October 18, 2020, 06:25 AM »
Ok so I might have screwed up big time....god I hope not.
So I installed the green drywall that's water resistant OVER some thin drywall and thats OVER paneling that is also OVER plaster walls. And yes I already mud and taped it all. I see a lot of videos showing the tub being screwed to the wall studs. But I can't do that now as there's 4 layers of walls in the way.

I was planning on putting backer bored around the tub any ways. So the main 2 questions are
1. Is it ok to screw the tub flange to the green bored? Since I'm planing on putting up backer bored all around it. Or am I screwed and have to tear down a whole wall?
2. What's the importance of having the tub flange directly agaist the wall studs?
Oh and it's also a fiberglass jacuzzi tub, if that makes any difference

Edit 10/20. Ok ok you guys won. I've decided to tear it all down to the studs. I'm actully almost done tearing it all down but guess what I found. The studs on the wall where I'm putting the tub up against are all facing the wrong way. So I have to frame a wall in front of it. It's a 200 hear old house anyways. I really want a nice long shower niche shelf going across. I promise to all of you that I am going to do it right the first time from now on. No more trying to cut Corners, that only takes more time and money
« Last Edit: October 20, 2020, 05:04 PM by I screwed up »

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Offline Bugsysiegals

  • Posts: 444
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #1 on: October 18, 2020, 08:06 AM »
What do you mean by putting up backer board?  I can tell you by first hand experience the Green/Purple drywall are not water resistant and will mold over time with direct water contact ... at least it’s the case if the paper peels back on the edge or any other area is punctured and the chalk becomes exposed.

Whoever remodeled my bathroom last used drywall, I assume Green/Purple, and did not caulk around the edges where the tub and surround meet the drywall. We’ve a new exhaust fan which is rated for an even larger room but even still the hot showers leave the mirrors fogged and moisture on all the walls/trim ... not sure if this is normal ... but this has led to the drywall peeling at the edges of the tub/surround and mold has developed.

I’ve now to remodel the bathroom and have to research how far to extend the cement board past the tub in order to prevent any drywall peeling and future mold...

« Last Edit: October 18, 2020, 08:25 AM by Bugsysiegals »

Offline Peter_C

  • Posts: 931
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #2 on: October 18, 2020, 10:20 AM »
Are you tiling after tub install? Is the tub also going to be a shower? If so Schluter Systems Kerdi is designed to go directly over drywall, and is one of the top tiling systems in use right now.

My concern with so many layers of walls is...are they flat? If not tear the wall down to studs, make them flat with shims and planning where needed, then install drywall, Kerdi and tile away.

Are you going to set the tub in a bed of mortar?

Offline afish

  • Posts: 125
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #3 on: October 18, 2020, 10:25 AM »
Im a little confused on what you have going on to but will try to help.  First I would seriously look at removing that entire stuff sandwich you have going on down to the studs.  Drywall and wood paneling have no business being around a tub.  (sorry I know you didnt want to hear that) but its going to be a lot worse if you install and tile everything only to rip it all out in a year or two.  As far as the securing the tub.  Tubs can vary a lot some stand alone tubs such as the steel and cast iron tubs dont need to be secured to the wall and have no nail flange they are heavy and have no flex.  I think the fiberglass tubs have a flange to help support and minimize movement.  Not sure if you have ever used one before but most have some flex to them and water is heavy plus the more pointed load of people stepping around in the tub.  I usually like to fill under the tub with either cement or LOW expansion foam to help prevent extra flexing.  Some manufactures require it some already have the tub mounted to a skid so it varies widely.  Stay away from any green/purple board in a tub surround. Your 3 best options in my opinion are 1. Densshield which is almost like drywall but has a thick waterproof coating over it (its just about as easy as drywall) 2. One of the foam type (schluter) systems. 3. cement board ( I prefer to go over cement board with a fluid applied water proofing as well) like Mapei's water defence.  #1 is easiest but I trust it the least even though I have never had or seen a failure. #2 is going to be easier than #3 but more expensive. #3 is going to be the most labor but cheaper and the most bullet proof in my opinion.

Offline Sparktrician

  • Posts: 4036
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #4 on: October 18, 2020, 10:35 AM »
One thing not yet mentioned is to NOT set the cement board (or any other substrate) directly on the top of the tub.  Set it 1/4" ABOVE the tub and over the flange so that proper caulking can be done after the tiling has been completed.  NEVER screw the substrate to the steel tub flange.  Doing so creates a pathway for moisture to turn into rust. 
- Willy -

  "Show us a man who never makes a mistake and we will show a man who never makes anything. 
  The capacity for occasional blundering is inseparable from the capacity to bring things to pass."

 - Herman Lincoln Wayland (1830-1898)

Offline Bugsysiegals

  • Posts: 444
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #5 on: October 18, 2020, 01:34 PM »
One thing not yet mentioned is to NOT set the cement board (or any other substrate) directly on the top of the tub.  Set it 1/4" ABOVE the tub and over the flange so that proper caulking can be done after the tiling has been completed.  NEVER screw the substrate to the steel tub flange.  Doing so creates a pathway for moisture to turn into rust.

I’ve a tub which also is going to be a shower with tile and going to use cement board. I planned exactly what I think you’re saying ... cement board with 1/4” gap from the top of the tub flange and notched where the flange is secured so it doesn’t touch the screw/nail, and then the tile with thinset/mortar will run down past the flange with a 1/8” gap between the top of the tub, finished with caulk ... sound about right?

Do you run the cement board flush with the exterior of the tub or past the tub by “x” distance since water can get past the shower curtain and on the wall?

Offline Sparktrician

  • Posts: 4036
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #6 on: October 18, 2020, 02:15 PM »
One thing not yet mentioned is to NOT set the cement board (or any other substrate) directly on the top of the tub.  Set it 1/4" ABOVE the tub and over the flange so that proper caulking can be done after the tiling has been completed.  NEVER screw the substrate to the steel tub flange.  Doing so creates a pathway for moisture to turn into rust.

I’ve a tub which also is going to be a shower with tile and going to use cement board. I planned exactly what I think you’re saying ... cement board with 1/4” gap from the top of the tub flange and notched where the flange is secured so it doesn’t touch the screw/nail, and then the tile with thinset/mortar will run down past the flange with a 1/8” gap between the top of the tub, finished with caulk ... sound about right?

Do you run the cement board flush with the exterior of the tub or past the tub by “x” distance since water can get past the shower curtain and on the wall?

I prefer to notch as you noted, lay a 1/4" spacer on top of the tub, secured with blue tape, then put a bead of caulk on the top of the flange before setting and screwing the substrate to the framing.  This first bead of caulk prevents (hopefully) capillary action from wicking water up into the framing.  When the substrate has been fully attached to the framing, I remove the 1/4" spacer.  Once the tile job has been completed, I caulk the 1/4" space, being as sure as possible to force the caulk up to meet the previously-applied bear of caulk. 

As for the second question, I prefer to run the waterproof substrate at least 2" past the outside edge of the tub, then cover it with border tiles.  Caulking here is as important as it is inside the shower curtain. 
- Willy -

  "Show us a man who never makes a mistake and we will show a man who never makes anything. 
  The capacity for occasional blundering is inseparable from the capacity to bring things to pass."

 - Herman Lincoln Wayland (1830-1898)

Offline Holzhacker

  • Posts: 977
    • www.aic-chicago.com
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #7 on: October 18, 2020, 05:49 PM »
This is just stupid, this must be a joke or somebody watching way too much hgtv.
Tear all that junk off and start fresh.
If there is a shower head the green board is NOT compliant for that installation per the manufacturer.
"The Code is not a ceiling to reach but a floor to work up from"

Offline DeformedTree

  • Posts: 940
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #8 on: October 18, 2020, 08:09 PM »
tear it all off.  It's just a tub space, not that much material, and make the bathroom a few inches bigger.

Offline Cheese

  • Posts: 7782
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #9 on: October 18, 2020, 09:20 PM »
I hate to pile on...but I will.  [smile]

If this were my project I’d take it down to the plaster walls. The wood paneling has absolutely no business being sandwiched between wall surfacing materials. It will only suck up water and eventually destroy whatever wall treatment you decide on.

I’d keep the plaster because of its structural qualities and its soundproofing. I’d fill in with cement board and then pull both products together with some Schluter Kerdi laid over both of the areas. Then install edging, thin set and tile...grout...let it cure...you’re finished.

Offline mkasdin

  • Posts: 306
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #10 on: October 18, 2020, 09:53 PM »
Tear the whole bathroom wall sandwich out. You can check for mold once you have it to the bare  🐻 studs. Then use the appropriate substrate as recommended above. I’m not a bathroom remodel expert but what you said is a no-go. Anywhere there is tile you should have a waterproof membrane. A floated bed of mortar is probably the best, the schluter is also very good, but pricey $$

Offline Jim Metzger

  • Posts: 80
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #11 on: October 19, 2020, 10:36 AM »
You mentioned it is a Jacuzzi. Have you planned for the access panel to service the pump and is your electrical up to code for a wet area? Also know that caulk will not stick to caulk. If you get the caulk joint between the tub and tile wrong you cannot just go over it.


Some people will recommend using mortar or low expanding foam under the tub. If it is a Jacuzzi make sure you can do that.



Do not under any circumstances use a bubble bath in a running Jacuzzi. It will introduce air into the system and cause the pump to cavitate.


I'd also recommend a hand shower to rinse the tub when you are done soaking.


Do it right the first time.


Offline Sparktrician

  • Posts: 4036
Re: Can a tub be screwed to green bored or am I screwed ?
« Reply #12 on: October 19, 2020, 12:24 PM »
Why is it that there's never enough time or resources to do it right the first time, but there's always enough time and money to do it over and over again?   [sad]
- Willy -

  "Show us a man who never makes a mistake and we will show a man who never makes anything. 
  The capacity for occasional blundering is inseparable from the capacity to bring things to pass."

 - Herman Lincoln Wayland (1830-1898)