# Rotten bathroom subfloor



## tallycat77

I have some rotten wood in the corner of my bathroom between the tub and the toilet. In investigating, I pulled some of the rotten wood out and now have a hole straight through. Not sure how it got to be like this. I had a leaking tub drain replaced and this may be the lowest spot in the bathroom where any water would collect. In addition, there is no underlayment over the plywood. I think placing some 2X8's perpendicular to the joists and replacing with 1" plywood would be best. There is a joist about 8" in from the wall, the other is on the other side in the kitchen. Should I take out the toilet and vanity, replace the rotten with new 1" ply and then put an underlayment on before I top with a faux stone laminate? The subfloor was topped with peel and stick tiles, which I am sure did not help with the moisture problem. Any advice or suggestions are appreciated. New DIY'r but have felt quite accomplished in my endeavors so far.


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## Mike Swearingen

The rotted floor damage may have been caused by just shower and bath users dripping water between the tub and floor, or through the stick-on floor tiles, over time. Any water hitting the floor from whatever source will do it eventually.
I don't know how your particular floor is built, but usually there is a subfloor layer, a "vapor barrier" layer of roofing (tar) paper if it is over a crawlspace or unfinished basement, and then the flooring level that the finish flooring is installed on. 
In my case for instance, which is typical, there is 3/4" plywood subflooring on the joists, a layer of overlapped tar paper (downstairs bath only - over crawlspace), a layer of 5/8" plywood flooring, 1/2" cement board and then ceramic tile.
You also probably have rot damage under the tub, but if the tub is sitting securely, I wouldn't worry about it right now.
You may need to remove everything but the tub to get all of the damaged flooring out. 
To remove the bad flooring, you will need safety glasses, a circular saw (use an old blade - you WILL hit nails), a crowbar, a prybar, claw hammer, etc. Use a reciprocating saw if up close to the tub or a wall. 
Adjust the depth of the circular saw blade so that it cuts only through the flooring, and NOT into the top of the floor joists. You may want to start a layer at a time. Be careful with a recip saw. 
Cut along the centers of the floor joists, so that you have something to nail or screw the new subflooring and flooring to. If the top of the joists are badly damaged, you can sister another joist along side of the old one with long screws. Install 14.5" crosspieces of lumber the same size as the joists between the joists, half under the old flooring for the same reason.
I always use pressure-treated lumber and plywood when repairing bathroom, kitchen or utility room floors, but that's your call. 
To make it easier to pry out and remove, I don't cut more than 2' X 16" pieces of the damaged flooring, but go back with as full sheets of plywood as you can, and stagger the joints of the layers.
Good luck!
Mike


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## Benhamcarpetguy

Tallycat,

It sounds like you have a good handle on the situation. If I understand what you're describing, that's the course of action I would take. You really want the floor to be structuraly sound, so replacing any rotted wood is mandatory. Between the 2x8's and 1" plywood I think you'll have a good solid base from which to work.

Then, depending on the type of floorcovering you choose, an appropriate underlayment. By fuax stone laminate do you mean real laminate floor? Like Pergo or QuickStep? 

Absolutely pull the toilet, the sink too if it's not too much trouble, but always the toilet and replace after new floor is installed.

You really do need to find the cause of the problem. Making an assumption and being wrong can be an expensive mistake. I could very well be from the leaking tub, or major moisture underneeth. If you have a crawlspace go under there and see what's happening. You may need to fix that area before moving foward.

Good luck,
Don


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## Benhamcarpetguy

I should also mention that whenever dealing with water-damaged wood, ventilate as much as possible. Wear a good dust mask as well. Mold can be quite dangerous when stirred up and released into the air.

Don


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## tallycat77

*More investigation on rotten subfloor...*

Thanks for the quick replies and good info.







I went under the house again this morning to do some more investigating and found a small drip running down the toilet drain pipe. I saw another small drip running down the back of the tub. I have caulked around the tub spout - but did not caulk around the very bottom (because there was a hole there...







) So I guess now any water that hits the spot flows to the bottom and down behind the tub. I guess I should caulk all the way around, huh? As for the toilet, I'm not sure if it is a leak somewhere in the pipe, the wax ring, etc... What is the best way to diagnose, or will I more than likely fix the problem when I pull the whole thing out? Back to the rotten floor... I think I can handle tearing out the subfloor in the bathroom (that is the only thing between the stick on tiles and the floor joists) but what about the part against the wall? What about on the other side of the wall in the kitchen? I don't see anything on the kitchen side like I do on the bathroom side (remember - hole straight through to the ground in bathroom) but the wall rests between two joists (~21" apart). I've still got a few questions about how to install these pressure treated 2X8's I got. Am I supposed to run the deck screws all the way through the joists and into the perp. 2X8? Thanks for the sage advice and patient approach.


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## Mike Swearingen

Is the toilet "loose"? Sounds like you have a wax ring leak.
You also have a supply line or faucet leak around the tub, if it is steadily leaking when nothing is draining.
Caulk is not the way to repair those. 
You need to open up whatever you need to, to find the leak and fix it, or your flooring repair is for naught. 
When sistering joists, all that you're doing is screwing or nailing them side-by-side at the same exact floor level, and _supported_ the same way. Nail or screw the screws completely through the new joist and at least 2/3 the way into the adjoining, existing joist. 
Let us know what you find. If you run into anything that you need help with, just ask. That's why we're here. We'll be glad to help you. 
Mike


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## tallycat77

*Rotten subfloor -- More info and questions*

I would not say the toilet is loose. In fact, I recently paid somebody to "stabilize" but don't remember seeing anything on the invoice about replacing the wax ring.
I went under the house right after a shower had been taken today and I would not say the leak is steady. The only thing I did notice when I was under the house (not right after a shower) were the drops of water on the toilet drain pipe.
Should I caulk around the entire tub spout?
I want to do this right, just need to make sure I am covering all my bases.
What would be some of the reasons for sistering the joists? They don't appear to be damaged. I was under the impression that I would be putting in supports perpendicular to the joists to support the subfloor in areas where there is not a joist.
How much of the subfloor should be replaced? Obviously the visibly rotten spots, but how much is too much? Thanks for the help!


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## floorman

If this is a small bath 5 x 5 then go ahead and tear it all out and start over not worth picking and choosing in this small area take everything out as suggested and cut the entire subfloor out and replace.
I would worry more about the choice of flooring for this area than the what part of the subfloor to tear out.In effect what you are puttingin is a laminate floor with a stone finish i think if i were you i would opt for the real stuff and forget this product altogether it is still new and i'm hearing bad things about it,haven't done any yet but the ones who have don't like it.
Sounds like you are in good hands here


tallycat77 said:


> I would not say the toilet is loose. In fact, I recently paid somebody to "stabilize" but don't remember seeing anything on the invoice about replacing the wax ring.
> I went under the house right after a shower had been taken today and I would not say the leak is steady. The only thing I did notice when I was under the house (not right after a shower) were the drops of water on the toilet drain pipe.
> Should I caulk around the entire tub spout?
> I want to do this right, just need to make sure I am covering all my bases.
> What would be some of the reasons for sistering the joists? They don't appear to be damaged. I was under the impression that I would be putting in supports perpendicular to the joists to support the subfloor in areas where there is not a joist.
> How much of the subfloor should be replaced? Obviously the visibly rotten spots, but how much is too much? Thanks for the help!


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## tallycat77

*Rotten subfloor - making progress with plans?*

Floorman - thanks for the advice and for being patient as I attempt my first major home repair. The area is small, 6x5 (not including the tub). I think I can handle getting the toilet and the vanity/sink out all right, but what about that tub?! If it is not necessary to remove (how can one tell?), then of course I'd rather not. I think Ell made some good point about the caulking and the leveling and the drain, but based on the view from under the house, this wood does not look like it has been wet (no marks like the ones running from around the toilet). What do you suggest as a floor covering? After I tear up the 1" subfloor, should I lay 1" plywood again? or a thinner piece in consideration of the hardy backer board and tile? Since this will be raising the floor, how do I handle reinstalling the toilet and sink? I'll glady buy a book or two on this subject if you have any recommendations. I just keep telling myself how accomplished I will feel when this is finished - not to mention my new tile floor (which I will more than likely install in the kitchen based on the same specs). Thanks!
Tallycat


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## floorman

If you can get the plywood out without any damage or loosenimg of the tub then do it.

With the sistering of the joists you can go a little thinner on the plywood use either 3/4 o.s.b. or exterior grade plywood.That should do just fine then the hardi or durock and then the tile.
After is all the plywood and durock or hardi is in check the toilet flange and see if it needs to lowered or raised,check that do that before you put all that stuff in,got ahead of myself there  .
You can cut the perimeter of the room and get as close to the walls as you can and then chisel or take a sawsall to it and get the rest.
Let us know if we can help some more


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## tallycat77

Thanks floorman-So I should pull out the vanity and toilet, remove the subflooring up to the tub and around the perimeter (so that all is showing are the floor joists)? Then I will need to check to see if the toilet flange needs to be raised or lowered (based on the depth of the new 3/4" plywood, durarock/hardi and tile) and make any adjustments. Adjustments: how do you raise or lower the toilet flange? It is PVC drain pipe, so I am guessing I would have to cut and replace with the appropriate length piece making the connections with epoxy and pipe fitting stuff. I assume the same goes for the sink connections. Then I am going to put down the new plywood. What size pieces do you recommend and how should they be positioned in the room? What kind of screws should I use for connecting the ply to the joists? After I get the ply down, I install the durarock/hardi (what thickness do you recommened - 1/4" or 1/2"?) and then I will be ready to install the tile. Should the vanity sit on the durarock or the tile? If possible, I'd like to try and knock this out in a weekend or 3 days. Thanks for all your help.


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## floorman

Yes,pull all that you can out of the way and then cut the pipe for the toilet flange as you suggested and then reattach.

The piping for the sink is less crucial but if it needs to be done then do it,probably will not make that big a differencs as far as that goes.
Stagger the plywood over the joists at half sheets making sure you stop and start a sheet in the center of the joist so that you get the support needed for that sheet,put the bigger piece in the area that will get the most traffic and the smaller piece behind the commode and the sink.
Use 1 1/2 deck screws to fasten the plywood and use construction adheasive on the joists before you drop the plywood to fasten it.
Use 1/2 rock or hardi and screw or nail every 2" on the seams and every 4 to 6" in the field,and don't forget the unmodified thinset under the c.b.u. use 1/4 notch to apply that,and make sure the seams of the c.b.u. lap the joints on the plywood by at least 6".
Let us know if there is anything else


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## toolgal1

*rotten bathroom floor*

Thanks for all the helpful tips! After putting in all new plumbing in the shower and then pulling the toilet up to find rot, I am now in the process of ripping out the floor  A woman's work is never done.....


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## mark marabella

can i use thin set mortor to level ouy my bathroom floor?


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## joecaption

Once the subfloors out take the time to check the floor joist for level, the time to do any sistering, trimming, shimming is before the subfloor goes in not after.


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