The big box stores sell little pieces of Sheetrock. Or they have plaster repair at most hardware stores. It's in a tub like joint compound and costs like $7.

"The big box stores sell little pieces of Sheetrock."

They do, never saw them? Buy a 4x8 sheet and cut it in the parking lot. It's only about $8.

Some sell smaller, 2'x2', pieces, some don't. Call around.

Buy a big sheet, score & snap it to roughly the sizes you need in the parking lot. Those 2' x 2' sheets at the BORG are about half the cost of a 4' x 8' sheet around here.

If I want to do it the "old-fashioned way," is there any kind of special plaster I need to use, or can I patch a large area with drywall compound? I did see the 2x2 foot pieces but they are half inch thick, which is much thicker than the layer of plaster that I have on my wall. I would need 1/4 inch thickness.

cleo,

my local lowes and Home Depot do not sell little pieces of Sheetrock, they do not sell single sheets either, only 2 sheets at a time. What big box stores have you purchased little pieces of sheet rock from?

You really don't need to use Sheetrock at all. What you do need is something to fill the space so that the joint compound is not so thick that it cracks and dries too slowly. 1/4" or slightly thinner plywood will work fine. For greater adhesion of the joint compound, cover it with self adhesive fiberglass mesh tape or aluminum window screening.

If you still have the wood lathe to fill the hole and just need plaster, you can use plaster of paris (most like your old plaster), or something like versabond drywall compound to fill the areas. The old plaster is probably fairly thick, so you could also screw or glue in some 1/4" or 1/2" drywall first to fill the void, and then use plaster or drywall compound on top of it to completely fill in the area.

Plaster of paris will dry very hard, so gradually layer it in to minimize the need for sanding. This is one case where a little is better than a lot, because you can always add more layers. You can use drywall tape on the edges where it meets the old plaster, but may want to score the old plaster so that you can embed the tape a little. Plaster of paris also has a very short working time (about 10 minutes), so don't mix up too much at a time.

Drywall compound will probably match almost as well as plaster of paris, and its available in mixes that are easier to work with (20 minute set time, several hour set time, etc.).

Bruce

"You really don't need to use Sheetrock at all. What you do need is something to fill the space so that the joint compound is not so thick that it cracks and dries too slowly. 1/4" or slightly thinner plywood will work fine. For greater adhesion of the joint compound, cover it with self adhesive fiberglass mesh tape or aluminum window screening."

This is not good advice. Buy the drywall, tape, mud, finish, prime and paint.

Plywood or other thin material such as luan will no more "suck in water" than will Sheetrock. If you can find scraps of 1/4" Sheetrock - not any easy task as this is a rarely used thickness - use it if you wish. If the void to be filled is actually 1/4" deep, however, you will wind up with a bulge after adding the joint compound and have a much more difficult task in smoothing out the repair than if you use something slightly thinner than 1/4". Of course you will need to tape edges, spread the joint compound, sand, prime and paint. Buying an entire 4x8 sheet of Sheetrock is completely unnecessary for what should be a simple repair of a relatively small area.

yea some places have smaller "remnant" pieces of drywall, usually due to some damage to a whole sheet

It depends (regarding the drywall size). There are three Home Depots in the city South of me; one only sells full sheets, but will sell single sheets. The other two both have smaller sizes that are precut in a couple sizes. One is a very high-end area, the other in an area with lots of older homes. All depends on the store.