Thursday, April 12, 2007

All Keyed Up

For those of you not familiar with it, a plaster wall relies on the plaster that smooshes through the lath to keep it on the wall. The strips of plaster that hang off the back side of the lath are called “Keys”. The most common reason for plaster failing in an old house is broken keys.

Today I started in on the plaster in the bathroom. I started on the wall with the door because it will be the last place you look when you enter the room. It went pretty well. It took me a few minutes to sort of get use to the whole hawk/trowel relationship again. I was also pressing too hard at first as I was applying the first coat of plaster. It was like I was treating the lath more like a cheese grater than wooden plaster lath. I got the hang of it after a few minutes, though.

Above is a front and back shot of the door wall. You can see how the plaster oozes through the lath to form the keys. Once it sets up, those keys will keep the plaster on the wall. I think I’m still pressing a little too hard. The keys don’t need to be that large, and it’s just a waste of plaster.

The front view represents 2 coats. If I remember correctly, the first coat is called the scratch coat and the second coat is called the brown coat. The scratch coat is coarse plaster that forms the keys. The brown coat is put on after the scratch coat is hard, but before it completely dries. I waited over night to put on the brown coat. The final coat will be the finish coat and that is just a very thin skim coat to smooth any imperfections and give the surface a nice smooth finish. If done properly, there is very little sanding involved. It remains to be seen how “properly” I’m able to do it.

I have come up with a different system over my kitchen plaster debacle. When I plastered the kitchen I made large batches of plaster in a black plastic tub that was about 2X3 feet. This time I’m using a much smaller tub and I mix smaller batches at a time. Hardly the way a professional would do it, but as we all know, I’m not a professional. There is no point in me trying to act like one if I know I’m not. Right?

By making smaller batches I don’t feel as rushed. When you know you have 20 pounds of plaster slowly getting hard in the tub there is an impetus to get to it. I now make just enough to fill the hawk twice. It’s more work, but I get better results, or at least I hope I will. So far, I’m not completely disgusted with my work, so I’m off to a good start.

The other benefit to making smaller batches is that I don’t have as much waste – there was a lot with the kitchen – and I don’t have small, dried chunks of plaster mixing in with the new stuff. Small, dried chunks of plaster getting mixed in with the fresh plaster caused me endless problems with the kitchen. You’re going along, just as fine as you please, getting a nice smooth wall, and then you get one of these destructo-chunks on the trowel and it just ruins all of your work by digging a gash in the fresh plaster. That didn’t happen once today.

This is pretty much as far as I’m going to get for a week or so. I’m going to be shutting down operations tomorrow, as I’m getting ready to play tourist director for some visiting family members. I wonder if they know how to plaster. Hmmm, maybe as part of the activities for the week I could sneak in a day of plastering demonstrations. I think they’d find it fascinating, don’t you?


Readerman said...

Yes, I find it very fascinating. Thank you so much for the mini seminar in plastering. We are remodeling an old home with plaster walls, and I've seen a lot of "keys." Didn't know they had a name, but now I do. Really appreciate your sharing. All the best of luck.

Anonymous said...

Personally if I were a guest at a home that was in the process of being restored, I would love to help. However, knowing what a perfectionist that you are, I would prefer to work on something that isn't too critical. Maybe you could set them up cleaning tile?

Derek said...

What kind of plaster are you using? I was thinking of trying some plaster to skim some walls, but I had a hard time finding any at the stores I frequent. I've looked online, and there seem to be quite a few different kinds, looks great so far.

Greg said...

The base, or scratch coat is a product called Structo-Lite and the finish coat is Diamond Finish Plaster. The brown coat in between is a mixture of the 2. The Structo-Lite is a US Gypsum product, and I think the Diamond is as well. I get them at a brickyard because the home center doesn't carry either product.

I have a PDF file with step-by-step instructions. As soon as I find it, I'll post it.

slateberry said...

OK you are mortal. I saw a picture of your hawk in a photo and thought, wow, he uses one of those! I assumed you mixed your plaster on the hawk. I've seen videos of pros doing it that way. But if you're mixing in a tub--well then that's more at my speed. Lesson learned: we don't have to do every single thing exactly like a pro to get good results, it just might take longer.

One of the things I love about your blog is the way you make things that seemed unattainable come into reach. The process of the job coming into focus, understanding the details and constraints, doing the research, solving problems as they arise, finding more questions as you go--I've lived this process many times as I've worked on my house, and reading about things I haven't tried yet in your blog is a wonderful road map of what's in store.