Interior walls - why skim coat with joint compound?

Question

Roughly put, my understanding of the history of interior walls is:

1. In olden days, plaster. Good/bad/indifferent - not everything was 3-coat. Good work took time. $$$
2. Drywall. Faster, cheaper. Largely supplanted plaster, ex in Europe and Boston. $
3. Then, skim coat. With joint compound. $$?

Apparently, skim coat looks better than straight drywall? If so, is that because the (taped & coated) joints are hard to hide?

Bonus question: if you're going to skim anyway, why not use veneer plaster, either over blueboard or over drywall plus a bonder? Am I wrong in thinking that plaster is much easier to trowel?

(Full disclosure: I'm going to do some drywall, for the first time. I have done some veneer plastering. I found the results more that adequate, and didn't think it was impossibly difficult - mostly, it set faster than I wanted. But, I'm far from a pro.)

Answer 1

I'm not sure if we're talking about the same thing with "skim coat", but it's just a higher level of drywall finishing for improved sheen management.

Level 1: This level means that your drywall joint tape has been embedded in joint compound, and nothing more.

Level 2: This next level means that you have skimmed a thin coat of joint compound over the tape and covered the drywall screw holes. You can stop at this level if you intend to cover with tile.

Level 3: For this stage, you apply a coat of joint compound to the tape and screws. Walls that will receive a heavy texture, such as knockdown texture, can end at this level. It would be pointless to progress beyond this level, since texturing is rougher than level 3.

Level 4: This is the classic drywall finish.

Here, you apply another coat of joint compound to the tape and screws and sand the dried compound.

Level 5: The highest possible level of drywall finishing involves applying a skim coat, if applicable. ... The two instances when you need a level 5 coating: the finish will be glossy and/or light will be coming from an angle low enough to highlight bumps and depressions.

https://www.thespruce.com/the-five-levels-of-drywall-finishing-4120152

Modern joint compounds are used for their ease of application, relatively quick drying, and light weight. I'm not familiar with the application of plaster over drywall in modern scenarios. My 1950s home did have plaster over drywall, but that's a much more involved process than simply skimming wallboard.

Answer 2

Skimming the entire surface with a looser joint compound just makes the entire surface uniform. It is almost impossible to get a uniform appearance without it but I guess it depends on how hard you look and the sheen of the paint. I have never skim coated with blue board and plaster but I had a job quoted both ways and plaster was almost twice the cost.

Answer 3

In my house built 20 years ago, we opted for a 2 coat plaster system that is in my area called "hard coat plaster". The plasterer did a terrific job and swirled the finish to my wife's liking. (you get the picture) WE (she) then had the painter paint the whole house with a semi-gloss paint finish which she can clean to remove spots. Flat finish paints are always used with "dry wall" jobs to try and hide the taped joints, which can always be seen. The walls and ceiling are semi shiny and looks great. No tape joints, no marks that she can't remove.