I worked for a short time with a guy who made furniture
as a hobby.

I've heard him mention "milk paint" several times. I guess
it's used because it's a very tough coating , and I suspect it
maybe heavy as well. Don't really know

Never tried it myself and I would be reluctant to do so since
so many other systems are proven and readily available.

I've tried several other systems of coating my planes,(auto,dope,etc),
but I prefer the latex method. Inexpensive,easy, and in any color I want.

Regards
Roby