the approach i use when it comes to varnish and sanding is that i use 220 sandpaper with a relatively soft backing.

the purpose is to simply scratch up the surface for adhesion for the next layer and to flatten out sags, drips or runs.  When i am working on taking down a sag, drip or run i use a more solid backing to ensure i cut  the 'bump' down to a smooth surface.

for between coats, i have used lacquer thinner but more recently water.

after sanding i vacume the surface and wipe it down with the lacquer thinner or water using a disposable paper towel.  its' just important to let the water dry before the next coat....vs lacquer thinner evaporates quicker (but you have to wear a ventilator) 

the most important thing to me for getting a good varnish job is to get those runs and drips knocked down for a smooth surface and to just really work to try to keep the dust down....which starts with a clean surface and is also about not having a lot of air movement in the varnishing area. 

having a good, properly positioned light source is also important to clearly see where you have applied the varnish and where you haven't so you don't accidently miss sessions.

denatured alcohol is not something i use on varnish.  

h

just as a clarification....before the first coat of varnish goes down, i use either denatured alcahol or the lacquer thinner to clean the epoxy surface.   all you are really trying to do is ensure you have a clean surface with no contamination.  either will do the job. 

the first coat of varnish will tell you if you had a contamination problem on the underlying surface by either developing fish eyes or a brittle textured surface (vs smooth and glassy).   if your first coat of varnish goes down fine,  as long as somebody doesn't spray off a can of WD40 in your work space after your first coat, you are usually good to go.

howard

Like Howard I use water and paper towels to clean up after sanding between coats of varnish. After the first couple of sandings I also sometimes use a tack rag, I wait until then so that there's no chance of contaminating the epoxy surface.

Unlike Howard, I use 400 wet & dry sandpaper. I also wait until the 3rd coat before I start sanding, just so I don't get into the cycle of put it on, sand it all off, repeat until varnish is gone.

Good luck,

Laszlo

Be Very Careful using lacquer thinner. It’s quite the volatile stuff, explosive vapors easily produced in a very short time when used for surface cleaning. You’d be unpleasantly surprised how easy it is to touch off from whatever ingition sources might be present when used. Too it’s not at all good for any of your mucous membranes or lung tissue, skin or liver either. Use a well-fitted respirator and PPD equipment if you need to use it, carbon filter-equipped.

Were I you I’d opt for plain water, or maybe whatever’s available as a shellac thinner where you are over lacquer thinner.

just another note on how a little sanding helps.

sometimes it is hard to see where you have put down fresh varnish if the underlying surface has not be roughed up a bit.

that said, if its going on smooth, and you happen to have 400 grit...that works fine too.  first couple coats, per laszlo's comment, i am typically going to go very light.

h

Denatured alcohol isn't sold under that name in Canada. Check your outdoor and marine supply stores in Powell River for alcohol stove fuel. That's denatured alcohol with a different name.

Shellac thinner is also simply denatured alcohol.

hokker