Not to long ago I had the chance to do something I hadn't done in quite a few years (like 15), and that was to make some curved mouldings from plaster. Since all the mouldings were going to be painted, plaster was the obvious choice. Many mouldings back in the old days where made from plaster and I'm sure that there were many technique for making them. I have developed some techniques as well for making them and I'm going to share them with you today, but first let's look at the alternatives.

You might thing that going through the trouble of making plaster moulding wouldn't be worth it. Well, if you price these moulding out you'd find that it's no trouble at all to make them since you'd save a TON of money. Just one side of the arch shown above would have cost me about $150.00 to buy or $300.00 to complete it (both sides) in flex. Prices ranged from $12.00 to $20.00 per foot and then there was a setup fee because my profile was one that wasn't stocked. Making the mouldings out of wood was an option and if I had some more time or if the mouldings where stained I would have opted to do so. The drawbacks were getting a knifes made ($300 to $500) milling and gluing up all the curved stock and making the jigs for cutting the moulding on the shaper. With eight archways and arches and none being the same, that in itself was a lot of work. So spending about two days and a material cost of $60.00 for making the mouldings seemed quite a bargain.

It goes without saying that there is a fair amount of prep work involved in doing something like this and that care should be taken when doing it. Two critical parts were 1: making sure all the jambs were as true as possible and 2: getting all the radii of the arches correct. Since the plaster doesn't move, if you get it wrong you're screwed. . . or at least you'd have to make it again. Getting the radii correct amounts to a few simple geometric steps and reducing the radius by whatever the reveal on the trim is. Once you have done this you can set out to make the screeds, benches, platform and beams needed to make the mouldings.

The technique I use is called "shooting" the plaster, it is where you run the screed through the plaster to form the curved moulding. In the past and I'm sure in some places today craftspeople made what is called a "shooting bench" to make straight runs of plaster moulding. If any of you are fans of This Old House^TM you might remember an episode where they showed this very process.

The first step in making plaster mouldings is to set out and make what amounts to a screed or template which emulates the profile of the straight moulding you are using. In the past I've used such things from putty/drywall knifes to thin sheets of steel to make the screed, this time I used a thin sheet of galvanized sheet metal to make the screed. I purchased a 8" x8" square for a few bucks from my local Home Depot.

To make the screed I traced the profile of the moulding on a piece of 3/4" plywood slightly bigger then the mouldings profile. I made a pair 5" x 5" squares. I then cut the sheet metal to the same size and sandwiched it between the two pieces of plywood, screwing through the entire assembly to secure it. I then use my scroll saw to cut out the profile. Using the plywood gave support to the metal while it was being cut.

After cutting and a few minor touch-ups with some files got the profile just right.

I mounted the screed to another piece of aluminum bar stock. I did this so I could mount it to a beam to swing the screed.