Help with replacing subfloors

Old 12-25-02, 04:51 PM
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Help with replacing subfloors

We just started remodeling the bathroom. After removing
the vinly flooring, we found the underlayment (particle board)
has water damage We removed the underlayment and
found that the subfloor has water damage

I need help with the following questions....

1. What's the best way to replace the subfloors? These
look alot tougher than removing the underlayment.

2. How can I determine the cause of the water damage?
I suspect it's the toilet or the bathtub cuz they are
adjacent to the damaged wood.

Bathtubs can't leak (can they?). So only water coming
from the bathtub I figure is from water leakage coming
around the curtain when someone takes a shower.
Does this make sense?

Thanks for listening. Merry Christmas!

Old 12-25-02, 05:37 PM
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The floor damage could be caused by water leaking from the wax seal under the toilet or from water leaking under the edge of the vinyl flooring at the base of the tub from the tub/shower. It could even be damage from a pipe leak under the tub or in the wall.
Find out what has caused the damage, and take steps to replace or repair as necessary.
In any case, the way to remove damaged flooring and subflooring:
A. Get a circular saw (use an old WILL hit nails), safety glasses, a crowbar, prybar, and claw hammer.
B. Set the blade depth to cut the subflooring only (probably 3/4" plywood), not the joists.
C. Cut the subfloor back to the center of the nearest joists outside of the damaged area. Cut it into small sections (no more than 24") for easier removal.
D. Once you have all of the damaged flooring out, nail or screw 2Xs between the joists half under the good plywood. This will leave you half of a 2X to screw the new flooring to all around the opening.
E. Install a solid sheet to fill the void. Use screws about every 6" along the joists and on the new supports between the joists.
F. If the subfloor is over a basement or crawlspace, add a layer of 30-lb felt over the subfloor as a vapor barrier.
G. Then add the flooring over the subfloor, staggering the joints if you have to use more than once piece each.
When repairing joists and flooring under a "water use" area (baths, kitchen, utility, etc.), I always use pressure-treated 2X and p-t plywood, for when (not if) there is another leak. Then you only have to fix the leak and just let the p-t dry out the next time that something like this happens.
Good Luck!
Old 12-25-02, 05:39 PM
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Well, you got your work cut out for you but it should go well if you do the following things.

I assume that you have removed the toilet,vanity and the like but you still have the tub in place. You didn't mention replacing the tub but if it is staying, it woul be a good time to evaluate its condition as well as the possible leaking issue. Rule of thumb "If it involves water - it can leak!" You should thoroughly check out all the fittings and if need be, replace the tub drain assembly with a new one due to gaskets and/or plumbers putty can become brittle/crack and the leak starts. Toilets are another area but usually the wax rings may need replacement but also check water supply line and replace with "no burst" flexible lines - easy and good insurance. Don't forget to check your sink lines as well.

Removal of the existing subflooring, which may be 1x boards or plywood can be removed by the use of a circular saw and/or sawzall. Use a prybar to pull your subfloor pcs out once cut. ***Don't cut the floor joist when doing this and don't go below the subfloor in case water/drain lines are directly under it*** Once you have all this removed, replacement with 3/4" T & G plywood is in order. Apply construction adhesive to the joists before laying your sheets down and use screws in this application - no squeaks and solid!

Depending on what you are doing for finish flooring will determine your next step. If ceramic tile, nothing else needs to be installed but this is based upon the method of tile application. If done the old way with lath nothing esles is need. If with thinset, addition underlayment is needed. If vinyl flooring again, then use hardboard underlayment or particle board. The thickness that you will need will be determined by your existing door jambs/casing.

Hope this all helps!
Old 12-25-02, 06:53 PM
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OldGuy, Doug:
Thanks for the tips! We now feel confident to tackle
replacing the subflooring first thing tomorrow morning!

We've also found the source of our leak. Spraying
water on the fixtures in the shower caused water to leak
into the crawl space. We've re-inforced the caulking
around the fixtures and will retest tomorrow.

The next question is how hard do we look for
damaged subflooring? We've gone under the house
and the subflooring below the bathtub and behind
the wall looks ok from underneath. Just a few white
spottings. I guess this is mildew?

We were not planning on replacing the bathtub.
So is there a way to assess the subflooring under
the bathtub besides removing it?

And is the only way to assess the subflooring behind
the wall is to rip open the wall?

Again thanks for your replies. It was a wonderful
xmas present!

Old 12-25-02, 07:10 PM
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Just remembered something...what happens if the
nearest joist for the piece of damaged subflooring
is behind a wall? Is the only alternative to rip
open the wall and cut the damaged piece to
the nearest joist?

Instead of ripping open the wall, could one add
another joist and hammer the new piece of subflooring
to it?


Old 12-25-02, 07:23 PM
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To determine if the subflooring is sound, use a flat blade screwdriver and try to push it into the wood. If it seems relatively hard, it is probably ok. I would suspect that your partcle board was more damaged, swollen up and maybe even brittle.

As Old Guy indicated, you can put down some felt paper to act as a vapor barrier under your new underlayment. If you are seeing white underneath, this just may be residue from the water, mold would tend to be more porous, not like a boarder stain.

Subfloor replacement if required means tub removal unless the area under it is not damaged. In fact, your particle board (underlayment) may have only gone to the front of the tub, not under it. Usually the tub would sit directly on the subfloor then the particle board underlayment would butt up against the tub, this provided a stop for the front lip of the tub to provide minimal movement when the tub was filled and occupied. Replace just a section of the underlayment may not be feasible if you are intending on relaying vinyl flooring thus the entire underlayment should be replaced. Sometimes the built up adhesive may be show or the unevenness of the particleboard, especially if it is old, it would have swelled some. You could try and sand the edges of the patch and apply water putty but I don't rely on such methods unless alternative flooring is done. If any flexing is in the floor, the wood putty will break and tile applications would require some Durock underlayment - glued and screwed!

Normally, the subflooring would be cut at the wall studs, not replacing the subfloor under them. This would only be done if severe damage was done.

I do have a concern for your walls though, you didn't mention if you had tile over plaster type walls or sheetrock but I am assume plaster. This may have gotten soaked and may be damp but you would be able to tell the condition by looking through the access panel. Just make sure that you have corrected the problem. I have reservations about the splashing on the fixtures causing damage that you described. It may be more than that but you are there and I am here. Make a good inspection.

Hope this helps!
Old 12-25-02, 07:26 PM
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If this is the case, regarding the subfloor being that bad, then you would install another joist with it out far enough to install your new subfloor. Sometimes this may be a problem around the toilet but you have to box it in. The same process is similar if next to the tub.

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Old 12-27-02, 01:34 AM
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Doug, OldGuy:
Spent the entire day removing the vanity/toilet and replacing
the damaged subflooring. Wasn't so hard afterall. Especially
with all your help!

Your hunch was correct in that the leak was not from the
splashings on the fixtures. After your reply, we retested
and found the leak was caused by the pipe connection
behind the faucet. Wev'e since repaired the connection
and are now leak free!

Our walls are sheetrock and we have some minor damage
at the base. Nothing too serious. Tomorrow we
start installing the laminate flooring.

This website is GREAT and your help was invaluable.
Thank you so much!

Old 12-27-02, 06:05 AM
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I'm glad that you did further testing. Sometimes the obvious may not be as what it seems.

I was surprised to hear that you are putting in laminate flooring but PLEASE follow the directions completely. This wouldn't be my choice within a bathroom but the product can be installed in a bathroom.

You guys don't work too hard and good luck with the bathroom remodel!

Happy Holidays!

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