Remove the lath and plaster and apply the gyp right to the studs.

 

I would personally remove the plaster. Lathe....probably. Keep in mind that the studs on those older homes are very likely smaller dimensionaly than the 2x4 that we think of today. In my old house (1910) all of the original studs under the lathe and plaster are 3" instead of 3 1/2. not a big deal so long as you take that into account when doing other projects.

 

Tearing out the old will give you access to run new wiring, plumbing, HVAC if needed. I'd remove it if it were mine. If you decide to go over it, you can use 1/4"....

 

Do a little exploration to determine what the actual wall construction is.

I bought a home that was built in 1917. The studs were full 2x4. Lath was applied. After that there was plaster. After that was a 1/16" thick "China coat" of very hard and very smooth finish.

When I saw what was there, any DIY patching would not be acceptable and a profession would be required. - It all depends on what you are dealing with. - I tried to buy the house back, but could not afford it now because of the value because it was restored properly.

Dick

 

I would probably remove it all. Just keep in mind that this will change your wall thickness when you replace with drywall, so you may have to deal with this with your existing doors, among other things.

 

This is going to affect the value in you're home. If it were mine and it was at all possible to repair, I would fix it.

 

Depending on where and how it was constructed, some things you might encounter: Old plaster on wood lath is often pretty soft. It was put on with the idea that it squished through gaps in the lath and formed a hook down over the back of the lath to hold itself, forming a wall surface. Over the years those "hooks" break off and the plaster gets loose from the lath. There is no fixing that short of tearing out. The materials used were not like the plaster used later over rock lath or wire lath. Door jambs and window jambs were sized for the plaster thickness. If you drywall, they are going to need to be trimmed back, or you can shim the drywall out to match what was the surface of the old plaster. Having done this a buch of times, unless the house has some historical significance, I would get rid of the old plaster and lath. There is a good chance that the studs will be a full 2"x4" and not the 3-1/2x1-1/2 studs we use today. They are not likely to be straight either. Save some of the lath for shimming. If you gut down to the studs, you can rewire, and properly insulate. You'll have a much better job in the end.

 

I'm currently doing this to my house now.
Keep in mind when the walls are open, your imagination will run wild and scope creep will take over.