Advice on replacing old/rotting subfloor under bathtub?

Submitted by owmyball t3_zz2mpv in DIY

Hello all,

Looking for advice on how to replace this rotten portion of subfloor under this bathtub, preferably without removing the tub/damaging the tiles?

House was built in the 1960's, I believe this is the original subfloor. Unfortunately the previous owners installed (sigh) carpet in all the bathrooms and naturally this resulted in the state of the floor as you can see. We originally had a carpenter replace most of the subfloor (also seen in the photo) and had intended to replace the tub (and floor), but ended up putting it off and moving into the house, then having a baby and now we desperately need a bathtub!

We'd like to get the bathroom simply functional as quickly as possible. My FIL took a look and suggested I sawzall the floor at the tub, where the rotten piece is, and just replace that. Which somewhat makes sense, and if that will do for 5-10 years then that's what I'll do; but wanted to get other peoples opinion and make sure there's nothing wrong with that or there are no other easy alternatives? I was kind of hoping to just pop in another layer of subfloor or water barrier or something, to 'seal' off the rotten stuff, but the floor does deflect when stepped on and is clearly not in great shape.

I've included pictures of the tub, floor, and kick-panel behind the tub that shows the state of the subfloor behind the tub (also not great). Happy to grab more pictures or add any context, thanks in advance!

Images : Bathtub woes

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Comments

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TheBlueSlipper t1_j291qqt wrote

>preferably without removing the tub/damaging the tiles?

If you figure out how to do this, please let me know. I don't think it's possible.

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owmyball OP t1_j292a7c wrote

Yea, unfortunately that may be the reality of it. Was hoping there might be some kind of neat fiberglass insert or something that would have a lip that extends far enough off from the tub that it solves my problem, but I think that's highly unlikely.

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rearwindows t1_j2951xz wrote

As a contractor, I'm sorry to say that there is little you can do to fix this properly without disturbing the tub and tile. You can try to carefully pull off the bottom row of tile and you have a chance, but if one breaks, it's really hard to replace it. Demolition is your only real option to fix it properly.

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owmyball OP t1_j295aci wrote

Got it, thank you much appreciated your insight

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owmyball OP t1_j296oy5 wrote

A follow up question - how bad would you say the wood is? In definite need of replacement? Or...could be salvaged for a few years until a full bathroom replacement is done?

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rearwindows t1_j297goi wrote

Depends on the flooring used. A floating floor would be best. If it is not spongy feeling, it'll probably last a long time. The mold will get worse over time. Do not use a sealant on the wood. It'll trap the water. If you don't fix the cause of the water, it will begin to smell musty.

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owmyball OP t1_j298fvd wrote

Makes sense, thanks again! Also, as a contractor if you for some reason are in the Philadelphia/SE PA area and would be interested in quoting out replacement please shoot me a DM!

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Fweem t1_j29op87 wrote

You know, it looks nice and dry in the area under and around the tub. I would look closer at the shower door to see if that is where the water is coming. If so, then maybe all that needs to be done is re-caulking.

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owmyball OP t1_j29r8z6 wrote

I hadn't thought of that, thanks! After all the helpful replies Ill definitely spend a day or so trying to identify/confirm the leak, then act accordingly. Fingers crossed it really could just be the doors and I can squeeze a few more years of life out of the tub then do a nice full remodel.

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2001sleeper t1_j298m5w wrote

Where is the water coming from?

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owmyball OP t1_j29ay1q wrote

I believe it's from people exiting the bath, not the tub leaking. I will verify that though if I end up attempting to keep the tub in place

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2001sleeper t1_j29g1dh wrote

If you can’t find the source, it all has to come out.

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whabt t1_j29ozsr wrote

You could stop using it for a few days, let it dry some, plug the drain, and then fill the shower pan to see if the water is leaking from the pan.

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owmyball OP t1_j29rhuq wrote

Good call! We actually haven't used it in the years we've been here, so this is water damage from the previous owner. However I hadn't thought to put water in and plug the drain-great idea to be certain if the tub is leaking or not

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Formal_Ruin_8096 t1_j29vvzz wrote

Hey! I had a similar problem when remodeling this original 1961 main bathroom in my house. The subfloor had water damage even worse than yours and it had been laid before the interior walls, so removing it would have meant demolish half the main floor and I wasn't ready to do that....So based on my very limited experience, you need to first make sure nothing's leaking and that the damage is actually and only from excessive moisture in the carpet. Then , what I did was dremel the whole perimeter of the piece to be replaced. Took a bit of patience and few blades, but it wasn't difficult. I then added a few pieces of wood where needed to properly screw and support a new piece of plywood in.

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owmyball OP t1_j2axz24 wrote

Right on, great to hear from someone with very similar experience. I'm gonna spend a day testing the tub and making sure it doesn't leak, then likely doing the same. Otherwise it's a full renovation! Thanks!

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Formal_Ruin_8096 t1_j2bemk3 wrote

What's under the subfloor? If bathroom is above another room or crawlspace, be careful not to cut into the floor joists. You wouldn't want to create a weak spot right where all the weight of a full tub will eventually sit. Considering the relatively small size of the part you need to replace, I (very occasional DYIer) would definitely go with a dremel over a sawzall.

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owmyball OP t1_j2dpfsu wrote

Yep, kitchen is right below. 100% agree on Dremel vs sawzall for a precision cut

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chaykota t1_j2awtkk wrote

I don't think it's possible. but, I do like a challenge! Remove the bath panel and the bath legs, see if the sealant around the bath holds the bath up. If so multitool around the edges of the rotten floor. If you angle the blade of the multitool sideways you should be able to do it, it'll be tricky and annoying with the restricted space but possibly could be done. Then pva the edges of the floor that was rotting (they would still be wet and rotting and don't want that moisture passing into the new floor and it should just dry out if not too damaged already. Replace then floor with chipboard. You might have to do it in 2 halves if when you remove the legs the bath starts to drop, so maybe remove 1 leg do that bit of floor, then the next. Fuck knows, worth a try.

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skydiver1958 t1_j2b9mj0 wrote

My guess is water damage from leaks around the doors and from the carpet. IF the plywood is still ok( not spongy) then for now reseal the doors and lay some vinyl plank floor. Not ideal but from what I see you will be ok until the gut job which this bath needs.

As long as the drain is good and no leaks from shower controls a little silicone and cheap vinyl floor should smooth you over til gut time

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owmyball OP t1_j2dp8bi wrote

Rgr that, thanks for the input! Will definitely make sure the plywood stays dry after a lot of testing for any leaks in the tub

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