should I replace this subfloor?
 

Hi all,

We took out the vinyl flooring toilet in a rarely used bathroom in order to do some tiling, and found some very water-stained subfloor. It didn't feel wet or any different really from the rest of the subfloor. Do we need to replace this section of subfloor? What do you think?

Thanks a lot.

Attachment 44443

Vinyl flooring AND toilet, sorry.

Is that the subfloor or luan underlayment?

Todd
www.aloneeagle.com

I'm pretty sure it's subfloor. It looks just like the subfloor in the rest of the house. There were a couple of layers of thin plywood above it that we took off with the vinyl, maybe that was luan underlayment? I don't know what it is.

Just to be clear, it was vinyl, thin plywood, More vinyl, more thin plywood, and then this floor you're seeing here.

Good answer! You can cut that section, joist to joist, add additional blocking and attatch new plywood.
Then your CBU or crack isolation membrane :rockon:

*be sure your cbu is set in a bed of notched mortar

Todd
www.aloneeagle.com

Okay...I guess my real question is, do I have to? :) What happens if I don't?

If the ply is rotted, moldy and flexy then yes. If its just a dried out water stain and the ply is solid it may be ok. That's your call since we're only seeing a picture..

Todd
www.aloneeagle.com

How can I tell if it's rotted? It's not mushy or flexible or anything, or even damp, but it is kind of dark.

I guess better safe than sorry and replace it, but we have a lot to do and I'm just trying not to add to the list if don't have to.

If the plywood is rotten, the toilet is going to keep working itself loose again and eventually leak.

Looks like black mold to me.
Hit it with some bleach and water and see it gets a lot lighter.