Fixing a water-damaged plaster ceiling

Hola, amigos! It's been a while since I rapped at ya, but I've been busy with the whole professing gig. So here's the deal. About, I don't know, a year ago? No, more--it was before the pandemic. Anyway, we had a nice rainstorm, and discovered that we needed a new roof. Water seeped in through a break in the flashing around the chimney, and water really wrecks plaster, which is what our walls and ceilings are made from. I'll show the consequences in just a moment, but suffice it to say, we got the flashing repaired, and a while later, got a new roof put on. So there won't be any more water damage, but we still had to live with the consequences, all from a pretty tiny amount of water:

This was the most obvious damage, a good 3 feet long or more

Some ceiling stains, and cracking in the ceiling plaster

The ensemble

Well, from a different, much more pervasive leak (from the upstairs bathroom), I'd learned how to repair this kind of damage, after several years of living with some pretty awful stains. So, that's what I did again. 

Step one is make the damage much worse! You have to get rid of the damaged plaster with a scraper, a stiff wire brush, sandpaper and if necessary, with a chisel. 

As you can see, in some ways, the most problematic area was the originally pretty minor crack in the ceiling plaster--but when I started pulling material away from the cement underneath, it just kept coming and coming, so eventually I said "big enough," and stopped. 

Step two is to fill in all that damaged material with wallboard compound. I've been using this cool stuff that is bright pink, but that dries off-white. This is nice, because you're not tempted to sand or paint until it's really dry. It has a downside, however, which is that it contracts a lot and takes basically 12+ hours to fully dry on a large patch, so three days later:

Along the way, I decided to finally fill in all those little holes and cracks as well -- and there were a lot. There was also a thin crack running the length of the ceiling. This is pretty typical. to account for heating a cooling, the big concrete slabs that form the ceiling don't touch -- they have about a centimeter gap between them, and over time, the movement and the contraction cracks the plaster along those lines. Our house is full of them, and you can see that they've all been patched and repaired before (I'm guessing once every 20-25 years or so it's needed). That requires a somewhat different technique: you fill the crack with wallboard compounded, set a loose mesh fiberglass tape in that, all more wallboard compound to cover the whole thing. 

Step three, everyone's favorite. Sanding. All of these patches have to be sanded smooth so that they match the wall or ceiling material so that they don't stand out too much. It's a pain to sand the ceiling, a real pain. I had a funny moment. I asked at the hardware store if they had any suggestions to make it easier, and the guy said, sure, we've got a ceiling sander right here. I looked at it, and went, "oh, right. I've got one of those at home, but wasn't sure what it was for. Well, it helps, but it's still a pain. 

Step four, paint: the trick, of course, is matching the paint, but I've brought in big paint chips and found a match before, and the guys in the paint department actually like that kind of challenge, so we found a pretty compelling match. BUT WAIT: there is a much more important step 4A: buy a really, really nice stain and water blocking primer. Spare no expense on this step, because even years after water damage in plaster, if you paint, the stain will just come right through again. Like, in a few hours. You will never be able to paint over it until you've blocked it.

And here is the exact same patch of wall and ceiling that we started with, as of today:

No way, right? It literally looks new, and the pain match is basically perfect. Here's a wider view for context:

I did a ton of crack and hole repair -- and there is actually still quite a bit that's not done yet. But this is much more livable (and attractive) than before. Am I ready to do the whole rest of the house? There are significant ceiling cracks throughout the main rooms on the ground floor. My answer. Maybe some day.