Clairification for first time skim coat

I'm moving into a house built in 1940 and it has plaster walls throughout. The walls are structurally fine but there are years worth of dents and nail holes as well as a fairly rough and uneven surface. Ive been researching and it seems like skim coating is the best solution to achieving smooth, flat, uniform walls (Plz correct me if im wrong). Youtube and some blogs are telling me that the way to do it is trowel 2-3 coats of drywall compound (potentially mixed with 10-20% plaster) onto the wall and to cure/sand each coat before applying the next one. then just prime and paint. This post is mainly looking for advice/tricks as well as giving the internet a chance to tell me if there are major flaws in my solution/planning of the project. Any help is appreciated and I'd rather know now if my plan is flawed than wait till im hundreds of dollars into the project.

 

Drywall mud dries, not cures and typically sanding is reserved for the last coat only - you can usually knock down big ridges and lumps with the knife.

Big knife for this, 10-12".

The rest of the plan looks pretty good (though I would use straight joint compound maybe with just a little water added, I would not add plaster).

 

If you spend $1,000 on this your using WAY too much mud!

I see guys in commercial work skim all the time. Especially after they pull off the vinyl wall covering. the glue leaves a rough wall surface. They thin their mud down to about a first coat tapeing mud (fairly sloppy, think pudding, I add two grout sponges of water) and put it on with a knife, trowel, paint roller or even a airless paint sprayer. Then smooth it off with a 12" knife or a large knock down squeegee.

It seams everybody has their own way of doing it. You need to find what works for you. I have found that as I get better, and better with taping, my mud gets thinner and smoother.

If your skimming a lot, I suggest renting a drywall sander for the sanding.

 

good advice, happy to know im on the right track.

 

Depending upon surface condition which can vary widely, you may not achieve "perfectly" flat surfaces. The smooth part is simple. If you had a straight edge that could go from one end to another you would likely see wide variations in it's "level". I believe this is primarily caused by settleing and climate changes (N.E. Ohio here). But it could also be a matter of application. Some plasterers did not shoot for perfectly smooth, perhaps not even level. I'm not faulting them, it's sometimes a matter of what is necessary budgetwise. Therefore what I shoot for is "the illusion" of flat and smooth. Some warps or variations might be obvious enough for a heavy fill, you'll have to make that determination yourself and try to fill those first, especially if using joint compound (not watered down) but better to use setting type for heavier fills.
Mixing joint compound and true plaster is like mixing latex paint with oil base :S mitch17 is again correct on two points... Plaster cures, joint compound dries. I try to avoid sanding at all costs ! A customer once called the dust "insideous". Also if one sands between coats, a smoother surface is not as good a bond as one that is rough. So like mitch stated... after a coat is well set, knock down high spots with a knife ( I like a 6" but 10-12 is good too) before applying the next coat(s). Keep the knife fairly flat against the wall when doing this to avoid gougeing. Ironhand described very well how many professionals thin down and apply their mud. If you are working with a pan and knives, I'd bet against you getting it from the pan to the wall or ceiling this way ! I work with a hawk and trowel and you'd have to be pretty quick with the flip and loose mud not to wear it ! Indeed water down the joint compound so it's managable, but not too loose. As you apply the mud- think to yourself about less sanding. Each coat should make the next one easier and smoother. As I mentioned I use a hawk and trowel, particularly for this kind of work (skimming) WITH COMPOUND ONLY ! So useing a pool trowel works best for me partly because it leaves less of an edge line. You have to have a feel for the mud or you could leave ridges and valleys.