Plaster. The bane of existence for many historic home owners…and one of the greatest pleasures of owning an old home. When properly done, nothing beats plaster for aesthetics, durability, and sound insulation. It can be applied over brick, stone, wood and many other modern materials like drywall or blue board. It's exceptionally versatile because it can be shaped into curves or archways and decorated with many different finishes. If damaged, it's easily and infinitely repairable.
A great book for anyone tackling a preservation or restoration project is Dan Browne's The renovation book: a manual for self-reliance in the home. There's a good section on applying plaster to new walls or old. Some of the information in this book, written in 1976, is outdated. But, it's still valuable and you can pull some good stuff from it and update with material available now.
Another good resource is the U.S. Department of Interior's Preservation Brief #21. It outlines the accepted procedures to follow to qualify for preservation tax credits.
When repairing plaster is not an option, there are a few good methods for replacement.
To replace the plaster on our brick chimney in our dining and bedrooms, we got a quote for $1,500. For only 90 square feet, that was not within our budget. When time and money are not overly abundant, veneer plaster is the way to go.
This method uses "blue board", a mold resistant drywall. It's available at any big box store for around $12 for a 4x8 sheet. The sheets are covered with a rough paper that bonds well with veneer plaster. Two coats of plaster (a base coat and a finish coat) are applied over the blue board. The veneer plaster can also be covered with a gauged lime finish-coat -- the same coat that covers ordinary plaster.
When complete, the veneer plaster looks much more like original plaster walls and less like drywall.
Replastering over old wood lath -- old school
Preservation Brief #21 describes three layers of the old school method of plaster.
- Scratch coat. The first base coat put on wood or metal lath. The wet plaster is "scratched" with a scarifier or comb to provide a rough surface so the next layer of base coat will stick to it.
- Brown coat. The brown coat is the second application of wet, base-coat plaster with wood lath or metal systems. With gypsum board lath (rock lath, plasterboard), it is the only base coat needed.
- Finish coat. Pure lime, mixed with about 35 percent gauging plaster to help it harden, is used for the very thin surface finish of the plaster wall. Fine sand can be added for a sanded finish coat.
Here's a good primer to learn about applying plaster to wood lath: Plaster Base Installation
Replastering over new rock lath
Rock lath is a plaster board (gypsum), generally 16 inches-by-48 inches in size, and 3/8-inch thick. It became popular in the 1930s as a less expensive alternative to wood lath. It is nailed directly to the wall studs. Two coats of plaster are appied over it. The rock lath replaces the wood lath and the brown coat of the previous wet plaster system. The second coat is a cement plaster about 1/4-inch to 3/8-inch thick. The finish coat is then applied, which is composed of hard finish plaster, and is approximately 1/8-inch thick.