Learning To Patch Plaster Walls

As something that’s been in development since I introduced the topic two weeks ago, I’m happy to finally have checked repairing the attic stairwell off my list.

The situation happening up there wasn’t dire. Crumbling plaster and unattended holes are no one’s idea of a well-maintained home, but the holes were out of sight behind the closed attic door, and therefore, mostly out of mind.

After I upgraded the stairs from glossy brown to a non-slip sand-infused gray, the walls needed my full attention. The damage wasn’t from me (or either of us, just to be clear), but it definitely did provide a nice opportunity for me to practice my plaster patchworking skills in a place that was in need, but also still out of sight for the most part in case I screwed it up worse. Because sometimes that happens.

There was plenty to consider before I got started:

The house was built in the early 40’s, so there could have been asbestos in the plaster. Lead paint could have been a factor too, as it was apparent that the walls had been painted and repainted several times. Deciding to keep things chill and create as little dust as possible, I opted to patch the open wounds and seal in the offending issues, and then then clean up the overall appearance of the stairwell with some fresh paint.

I started by patching the major holes of the wall using basic all purpose joint compound; after researching my options, I found that most sources suggested using this for patching plaster, even though its traditionally applied to drywall, and that it was especially good to use if it was watered down just a little bit (thinner than you’d need it if you were taping drywall joints, but thick enough to still hold stiff on the hawk and trowel. Pete had about 1/5 of a 5-gallon bucket of joint compound left over from previous projects, so I seized that f-r-e-e opportunity (the stuff doesn’t spoil easily if you store it correctly).

I used the smooth edge of a notched trowel to really glob on in a targeted way, sealing in the holes that were especially large (the size of my palm).

The big holes may have been big, but they were still over lath, meaning that I really didn’t need to get into buying a drywall patching kit to correct the situation since the lath would act as a similar backing for the compound to hold on to. Over the course of 3-4 days, I applied 3-4 layers of compound, not obsessively worrying about how smooth the surface was but more so focusing on making sure that the compound, which oozed downwards with gravity and also sunk concave into the wall as it dried, began to cover the hole and become convex. Compound itself is easy enough to sand down, so if it dries proud to the surface that you’re patching, you can sand a little bit and take it back down to being level with the rest of the wall.

I also made use of having the trowel and joint compound out and did a thin skim coat over most of the wall, which had its own ripples and cracks and smaller divots from 70 years of settling and being generally banged up from carrying belongings up and down the attic stairwell.

It wasn’t perfect by any new construction means, but it is a hidden stairwell, and it is old plaster with its share of irregularities itself. To create a perfect stairwell wall, I probably would have taken down the plaster all together and hung drywall in its place. Never mind that, this route was f-r-e-e.

The dirty part involved sanding the wall smooth, and this all happened after the last coat of skim coating had dried for about 2 days. I didn’t want to create excessive dust (knowing it could be lead paint and asbestos infested) so I kept it simple and hand-sanded the areas coated in compound only to smooth it out. The places that were skim coated had very little excess compound, so it was more a matter of making sure the edges where it was applied flowed smoothly against the wall. No photos of the actual process; it was messy in there and I was fully covered with a face mask, gloves, and goggles to lessen the chances of me inhaling a lot of the compound dust and whatever else I was loosening inadvertently.

After an hour spent hand sanding using both a rough and smooth sandpaper, it looked like this. Note the dust drifts on the freshly painted stairs; I’d have been smarter to leave painting the stairs until after I patched the walls.

Letting all of the dust settle for another day, I followed back through with a damp rag to clean the walls (and what I could from the stairs) before beginning to prime and paint the patched surface.

The surface still wasn’t perfect; as I mentioned earlier, there was a bit of damage in the plaster itself that couldn’t easily be disguised completely. Irregularities like cracks (from the house sinking?) and waves in the wall (uneven joists? uneven plaster application?) and even a 2’x4′ piece of thin plywood over what I found to be a hole in the plaster that’s the size of my torso. Can’t imagine how that one happened; originally I thought it might have been access to the shower plumbing which happens to be right on the other side of the stairwell, but we didn’t remember seeing that access point when we gutted the bathroom shower last winter. Fixing an me-sized hole wasn’t really in the scope of what I set out to do, so I re-screwed the plywood back in place and continued on my priming way. Shush.

The matte finish of primer really does a lot to hide irregularities in the waviness of the walls, although it only covers the smooth compound patches about as well as a tinted moisturizer. While I considered dropping $5 on an OOPS bin gallon of flat paint (there’s always a lot of flat paint in our Home Depot discount paint stash, why, I’m not sure) but I saved my money and kept the project totally free by using what we had on hand, some leftover semi-gloss Behr Irish Mist paint that I used on the bathroom walls. It shows flaws a little bit more (as glossier paints do), but I think some of these scars would show through regardless of paint finish.