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Bathroom Floor Help Please

2107 Views 18 Replies 5 Participants Last post by  bigfishcatcher3
I have begun a project that has been long overdue- finishing my master bathroom and bedroom. I got started in the bathroom last night and I am running into major concerns with the flooring. There were serious areas of rotten wood near the old shower floor drain and toilet, so tonight I started removing the subfloor. I am worried that once I am done replacing the subfloor that it will not be as level as it should be for tile.

Should I finish replacing the subfloor and install the cement board before assessing how level it is? For what I am doing, I am wondering if a self leveling compound can be installed on top of cement board. Can you install tile directly to the self leveling cement compound?

Also, at what point is it best to install my tub, toilet drain, vanity, etc? I am moving the toilet and tub from the original locations.

Any help is very much appreciated. Thank You


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Those floor joist look really narrow.
That's the width spacing and free spans of the joist?
How thick is that subflooring and is it T&G?

Your also missing foil tape on the duct work joint.

Yes the floor joists are very narrow. Im guessing about 12oc. The subfloor is 21/32 tongue and groove. What do you think? And yes there is no foil tape. Its amazing the things that are discovered doing these projects. That is a minor one. What do you think about replacing?
Very narrow is not what the guys need for info. Please get back with the info I requested. Later today the real good tile people will be home from work and will get you up to speed.
Joists are indeed 12"oc. Free span I will have to check tonight when I get home.

Since you're partially there, you may want to consider removing the rest of the subfloor. This would make it easier to evaluate if the joists are in plane. This will also make it easier to run the new plumbing to its new location.

Once exposed, you can sister the joists to make them all flat.

So your joists are 12" o.c.? What size are they? Do you know their specie and grade? I see you haven't gotten around to answering the span question. Haven't been back in over 3 days. Must be too busy working on the project.

Edit: Oh, I see you're online now.

By the way, I know Henry's Self-levelling compound is not approved by the manufacturer to go over cement board. You can certainly put it down before the cement board. Or, you can make up for it with the thinset, when you lay your tiles. I would use the self leveller before the cement board, though, another manufacturer may approve their product to go over cement board..I just haven't found it.

Or, as mentioned by JazMan, you could sister additional lumber to the existing joists. However, it will be a pain in the ass to get your drill/driver in between 12" O.C. joists, especially with another 1.5" inches taken up by the new lumber. You also have to keep the new lumber at the right height, while trying to attach it to the existing joists.
Yes sorry just downloaded the app to my cell and reading while driving home. I did remove the rest of my subfloor and switched all my pvc around fo the new layout while the floor is up. Spent 3 hours Saturday cleaning liquid nail off my floor joists. Good news though that joists look good and level. Next step will be sistering joists. I'll chec the span when I get home. Thank you.

Floor Room Property Wall Bathroom
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IMO floor don't have to be perfectly level just close, you can make up small differences with your thin set.
The joists are 2x12 and the span is 20 feet. They start at the right side of the pictures in hangers and then go 20 feet to the left.
The joists are 2x12 and the span is 20 feet. They start at the right side of the pictures in hangers and then go 20 feet to the left.
I find that hard to believe actually. (20 ft. unsupported span). Are you sure there isn't a supporting wall under there about half way? Also, maybe it's deceiving but just doesn't look like 2x12 at 12" o.c. in the pic. Maybe it's the shadow from the flash.

Yes. They are 1.5"x11". 12"oc and span 20 feet.

Wood Ruler Floor Plywood Ceiling

Floor Wood Hardwood Flooring Plywood
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Wow. Ok, the 12" o.c. is obvious. But I don't know of any species of grade #2 (commonly used for joists), 2x12" that meet minimum specs of L360 deflection at 50 lb. live and 20 lb. dead load for ceramic tile. Those joists are rated for vinyl and carpet which is what minimum code requires. The minimum criteria for code is L360 at 40/10.

It's not safe to install tile when the joists are overspanned. I'd like to see something around L480 or better. BTW, stone tiles require min. L720, just for reference.

Is there anyway to build a supporting wall under, or sister the joists? Sistering even just the center 2/3's would do it. Since the ceiling appears to be unfinished, sistering would be easier.

I looked at the pics again and wondering which way is the facegrain of the plywood going? Top and bottom grain should be the same on the sheet, but should be running perpendicular to the joists.

Yes it is perpendicular to the joists and that's how I will install the new. Please give me more info on sistering. I would like to not build a supporting wall in the middle of my basement game room if I don't have to. Thank you
Sistering= screwing/bolting new lumber to the side of existing to make it stiffer. Doesn't have to be same size as old. You can use 2x6 2x8 2x10, even 3/4 ply glued and screwed will do it.

Would you just sister it the width of the bathroom or the full 20 feet? Would it do any good to run 2x4 flat and flush with the top of joist in between? I was going to do that were my seem in the sheathing falls because I probably won't be using tongue and groove. What is better 23/32 plywood or 23/32 osb?
Sister the whole length if you can. The most flex will be towards the center of the span. I don't know how accessible the joists are.

You have to install blocking under all unsupported ends. (the 4' ends). I don't think 2x4 flat will be enough though. Why not install some joists under the ends?

You removed all the subfloor in the room right? If you wanna install just one layer you should go with t&g. Otherwise either do lots of blocking or also install an underlayment over the subfloor, 3/8" B/C or thicker.

3/4" Subfloor grade ply or OSB subfloor? Well I'd probably go with ply, but if you buy a premium OSB like AdvanTech you're doing good. Most would say premium OSB is even stiffer than ply. But with 12" o.c. I don't worry about that.

Before i did the sistering I would check all the joists and make sure none have sagged over the years. If they have now would be the perfect time to jack them up, then sister. May make your work later a lot easier
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