As I’ve mentioned before, plastering is a lost art. And to the people who used to do it for a living, I’m sure they said “good riddance.”
First, you had to put up lath, which originally was thin strips of bark or leftover wood, whatever you had available. This was nailed to the frame and a “brown coat” of plaster — a mixture of lime, sand, and water, mixed to the consistency of toothpaste — was applied. Some of the plaster (the “key”) squeezed through the lath and dried, which is what held the whole thing up. Next came a “scratch” coat of plaster — same ingredients but different ratios — which was a little finer than the brown coat. This was sanded down and a final coat was applied, which was also sanded to create the final smooth surface, ready for painting.
The good thing about plaster was that the materials were cheap, and as long as it didn’t get wet it would last forever. The bad thing was that it required a lot of time and labor, was horribly messy, and the walls were never, ever straight.
So imagine everyone’s delight at the turn of the last century, when drywall was introduced — it was cheap, it was flat, it was easy to install, and it didn’t make a mess. Unfortunately, it wasn’t appropriate for a 1760 mansion, so we couldn’t use it.
But we could cheat a little. Rather than install lath and a browncoat, we used “blueboard,” which is really just drywall that is moisture-resistant so you can apply wet plaster over it. That saved about half of the labor costs, but didn’t save the mess as they sanded the two coats of plaster. I imagine we’ll be blowing plaster dust out of every nook and cranny for the rest of our lives.
We also cheated on the ceilings. Rather than patch all the cracks and the holes made by the insulators, we just put up blueboard and a coat of plaster. That saved a lot of labor at the expense of the crown molding in some of the rooms. But since the blueboard was only a quarter-inch thick, it seemed a reasonable compromise.