Scratch Coat
No more excuses so this weekend is trying the scratch coat on the wood lath. I do a final pass with some more plaster washers just to make sure I didn’t miss any loose areas. I also put down some PlasterWeld around some of the spots that don’t have a lot of lath to grab on to. There’s some spots in the room like above doors that have crumbling plaster that I need to rebuild, but there’s only one lath so hard to see how a key can be built. In these cases I’m hoping PlasterWeld will provide some of the adhesion if I can’t get a good key,
I mix up a batch of the scratch coat and of course right out of the gate I forget the rule to start with water and add plaster to the water instead of the reverse. Because of that, I have to do a bit more mixing to get all of the dry plaster moistened. After I get things mixed, I add goat hair to the mix. The purpose of goat hair is to provide extra grab to the walls. When I attended the seminar, one of the instructors said it was no longer necessary because the modern formulation of plaster had enough adhesion. He said in the past with varying quality of sand, goat hair was needed to cover up for poor sand, but in the modern production they have better quality control. But the plasterer said he still uses goat hair and considers it a belt and suspenders approach where adding it won’t hurt and only would be a benefit. So figuring I need all the help I can get, I add the hair.
Adding goat hair.
Goat hair mixed in.
I make my way to each of the bare laths and apply the scratch coat. Because the spots I’m plastering are around windows or near a joint between a wall and ceiling, it’s tough to get the full-sized trowel into the spaces to spread the plaster. That’s the biggest challenge and at some points I end up using my hands to put the plaster down. At the seminar, the plasterer was talking about some plasterers actually throwing the plaster against the wall, so I figured I’d try that approach in some of the tight areas. Not sure if it’s correct, but it actually seemed to work well. The problem is that in a tight area, it’s hard to get a clean shot at taking the plaster off the hawk and getting the trowel into the area swiftly. I would try to navigate the tight space and the plaster would either fall off the trowel or I’d apply it so weakly it would just fall off the wall. But when I grabbed a blob of plaster and threw it against the tight spot, it stuck to the lath and then I could use a small trowel to smooth it out. One thing they stressed in the seminar was to not make the scratch coat too perfect. You need to resist the temptation to smooth things out too much and focus on getting the plaster on the wall and keyed in. Continuing to fuss risked pushing the plaster through the slots in the lath and it falling through the wall.
Starting application.
All done.
I get everything up on the walls and ceiling and things seem to be staying up so I give it a misting and wait a few minutes. I then go back through with a few pieces of wood scraps and give the plaster a scratch, hence the name scratch coat. The scratching gives the next coat more texture to grab on to. I keep a heater in the room to help things cure and then I’ll wait at least 7 days before doing the next coat.
Scratch coat
More scratch coat.
