Building the fire was fine, though I've noticed that the chimney liner is in pretty bad shape and I really need to sleeve the chimney.
While I was over there, I decided to take some measurements of the nooks by the fireplace. I noticed that there seemed to be more detritus on the floor that had fallen down from the ceiling, so I went up and pulled away a bit of the hanging-down paint/wallpaper shards. You can see the discoloration of the plaster where I had pulled off the old wallpaper and paint; it's mostly the color of the old wallpaper paste and leaching wood, and is normal.
Okay, so some of the plaster came down with it. I knew that the prior water damage had separated some of the plaster, so no big surprise.
Except that the lath that was still in place was wet.
On the inside wall of the fireplace, I found this loveliness:
No, that's not mold. That's where the previous owner had "fixed" the wall damage with vinyl spackling without actually finding the source of the water. It had actually bubbled up the surface and trapped the moisture behind it, deteriorating the old plaster and leaching efflorescent crystals to the surface.
So I spent the next hour and a half with the shop vac and a utility scraper going after the damaged plaster. I uncovered even more bad news: the trapped moisture had actually rotted the lath on the wall where the window is located. You can see the difference in coloration, and some of the rotted pieces here.
I gave up for the night. The whole wall where that window is is going to have to be taken down to the studs-- and it's an exterior wall, so it's gonna be not warm. The thing is, I can see now where the previous owner tried to "fix" this with mismatched pieces of something-or-other, so it's been around for quite a while. I'm a little frightened as to what I might find behind this wall.
The ceiling is going to have to be cut away to where the black line is in this picture
and all the plaster and lath will have to come out. Upstairs, I'm going to have to get into the eave crawlspace, find, and fix the leak. I have a pretty good idea where to look, but it's still gonna be a freaking mess.
This doesn't even begin to approach the ceiling in the dining room, which needs to go through a similar fixing process.
I suspect that my spring timeline may fall by the wayside. I can't really do a lot while it's still winter-cold outside. I suppose that on the good side, I'll be able to insulate that wall much better while I've got all the plaster and lath off.