A few months ago when I was looking to varnish some of my paintings I found a series of very helpful and informative videos from Gamblin. They have several videos up on ground application, oiling out, varnishing, reusing gamsol, and more. For example this video below covers ground application.It explains a few different ground and how best to apply them, how long it takes for them to dry. It covers both pannel and canvas as well. I found all this information very helpful when considering changing from acrylic gesso.
To view all of the videos click here.