Can you tell me what this is?
Tore off some damaged tile and drywall and found this behind it (next to a shower stall that had a leaking double track door). I don't find pictures of dry rot that resemble this (though that's what we suspect), and I'm wondering what we're dealing with here. Has anyone seen this before, and if so - what is it, and what needs to be done? It's hard to the touch and crumbly. Thanks for any help!
Here is a link that might be useful: