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Unread 04-12-2021, 06:34 AM   #1
MAS79
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Upstairs bathroom gut

Hi all,

I am currently renovating the last original bathroom in our 1955 colonial cape cod home. So far I've completely redone the electrical and plumbing and passed both rough inspections so now I'm getting ready to close things up. The floor where the original CI alcove tub was installed was close to 3/4 of an inch out of level on the long edge so I installed the new CI tub on a level ledger board and shimmed the feet using a combination of plywood and metal shims. It is rock solid and level left to right and front to back. However, now I have a 3/4 gap between the apron and the subfloor (5/8" ply) on the right side of the tub. I plan to "fix" that by adding another 1/2" layer of ply and 1/4" layer of Durock. That plus the thickness of the tile should hide the gap nicely. My question surrounds what to do at the threshold where the bathroom floor meets the 3/4 inch hardwood floor. If I go all the way up to the hardwood with the 1/2" ply and 1/4" Duruck I'll be level with the hardwood. Adding the tile on top of that will make it about 3/8" to 1/2" higher which I'm fine with. The issue is the threshold between the door jamb which will be marble or quartz (not sure how thick those thresholds typically are but I think they're 3/4") Assuming that's correct would it be okay to add the 1/2" ply and 1/4 Durock up to the door jamp and then just 1/2 inch Durock between the door jamb to get it level with the floor tile? Any advice is appreciated.

Thanks,

Matt
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Unread 04-13-2021, 02:26 PM   #2
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Welcome, Matt,

I think your plan is fine. Just be sure you set the Durock under the threshold in mortar and screw it down, and have the threshold fully supported by mortar when you set it on the Durock.

Will be good to screw down that 1st layer of ply. Remember, also, to install your 1/2" ply (no face grade lower than C, EXP1/Exposure 1 rated) so that it's long edge(s) is perpendicular to the floor joists and no seams lining up with the first layer. Don't screw it down into the joists, only into the first layer. Be sure to set the Durock in mortar and offset seams and corners per instructions.

I assume you evaluated your joists to ensure suitability for a ceramic tile installation?
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Unread 04-14-2021, 05:20 AM   #3
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Thanks for the reply Dan. I've evaluated the joists using the Deflecto tool and they're fine (2x10s, 16" on center, 13.5' span = L / 416). I also rebuilt a lot of the structure and added blocking to improve its strength. When I pulled up the original subfloor I found one joist was cut to make room for the toilet plumbing and it was completely unsupported underneath. The plumbers box under the tub drain was a complete joke too, so I rebuilt that as well. The original bathroom was there for the last 76 years, so it held up nonetheless.

The plywood subfloor was installed perpendicular to the joists, but the 2nd layer of 1/2" ply was not. I did everything else you noted except that. The bathroom is only 5 ft wide with the joists running in that direction. I don't have it completely screwed down yet and will pull it up and do it as you suggest if you think it's necessary. Thoughts? Again, thank you for your help.

Matt
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Unread 04-14-2021, 07:13 AM   #4
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Welcome, Matt.
Quote:
Originally Posted by Matt
The plywood subfloor was installed perpendicular to the joists, but the 2nd layer of 1/2" ply was not.
Hate to be the one to tell you, but you may as well not have bothered with that second layer of subflooring if that's the case. While it might make a nicer surface to work over, it didn't improve the subfloor deflection a meaningful amount. I would suggest it wasn't worth the labor or expense. See Post #10 in this thread in our Liberry.

I would remove that layer and orient it properly if that's an option.

My opinion; worth price charged.
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Unread 04-14-2021, 07:24 AM   #5
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Thanks CX. The second layer of ply wasn't installed to improve the deflection. It was installed to add height to the floor to hide the gap between the floor and the tub on one side. Does that change anything? I don't want to pull it up but will if you still think it's necessary.
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Unread 04-14-2021, 07:40 AM   #6
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Up to you, Matt. Your having only nominal 5/8ths" plywood for your first layer of subfloor I would consider the second layer mandatory, but the manufacturer of your CBU will say it meets their minimum requirement.

Keep in mind that when those requirements are established the testing is done with new material in pristine condition, near perfectly installed over joists with zero deflection and the test needs pass only once to be accepted.

I'd want the second layer.

My opinion; worth price charged.
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Unread 04-14-2021, 08:09 AM   #7
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Thanks CX. I will do it. Just talked to the lumberyard and good quality 1/2 inch ply is now $81 per sheet. Ouch. I wish I had read a little more before installing the 2nd layer. As my father always says..."Education is expensive". Thanks again.
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Unread 04-14-2021, 08:12 AM   #8
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one more question...the bathroom is only 5' wide. Would you install a full sheet and then a 1' piece or rip down the full sheet and install two wider pieces? If I go full sheet, the 1' piece will be against the wall away from the tub and won't get any foot traffic at all.
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Unread 04-14-2021, 08:19 AM   #9
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That's the option I'd choose, Matt, the 1 foot that doesn't get any foot traffic.

Education is expensive. Goodness knows I've spent a bundle.
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Unread 04-15-2021, 06:06 AM   #10
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Thanks for all the advice Dan and CX. What are your thoughts on waterproofing the floor? I plan on using Redguard (or something like it) on the tub surround, but hadn't thought about using it on the floor until the plumbing inspector mentioned it during my rough inspection. The old subfloor was severely rotted around the toilet and by the tub apron on the plumbing side, so I suppose it can't hurt. He said Redguard makes a band similar to Kerdi band for the gap between the floor and the walls and to use something like Kerdifix to caulk the seam between the floor and tub.

Thanks again.
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Unread 04-15-2021, 07:43 AM   #11
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Water proofing the floor, Matt, is more difficult that it might seem, since there's not an easy way to seal the toilet flange to the floor. You'd also need to be able to seal the edge of the circular cut out of the plywood encircling the flange/riser, not just the top.

Sealing the tub apron to the floor and side walls also requires some detailed work if you don't want to rely solely on caulk between the apron and the tile. If you're using 3/8" thick tile, and add the thickness of the mortar, you have just a bit more than 1/2" to apply whatever water proofing you decide on and still be able to hide it with your tile.

FWIW, I recently removed a tub from my 40 year old guest bath and there was only some very slight discoloration of the plywood near the tub apron, and none at all around the toilet.
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