Scrape! Yep, that’s the operative word—don’t sand, scrape! Sanding out the imperfections in the fill coats is theoretically possible, I guess, but not very practical. It would take forever. Take a look at the amount of resin scraped off in the photo below and then realize that all those darker, shiny spots are depressions that are still there after a substantial amount of resin has been removed.
You’ll want to sand. Why? Because it’s hard to convince yourself that you’re not getting to deep along the seams. The flat areas go slowly, but if you bear down on a seam you will cut into it, so you don’t.
As you scrape, you’ll see small drips lines, wavy lines, and random small depressions in the fill coat. If you do get a little bit deep, you’ll suddenly see a matrix of dots. You are not in the glass. If you took one more light scrape, the dots would vanish. What you’ve found is that the glass tends to rise up (bow up) very slightly as it is bent across a convex seam. This may only be a couple thousandths, but you will see the dots more quickly along a seam than you ever will out in the middle of a flat panel. That’s not to say that there won’t be an occasional ripple in the cloth in the middle of a flat area—there will be—but if you wet out your cloth carefully, ripples will be rare.
The point is, in the left photo below you will think “oh, crap” I’ve cut into the cloth. You haven’t. This pattern will completely disappear when the varnish is applied. It’s hard to tell when you’ve definitely hit the cloth—which means you’ll have a permanent visible pattern under the varnish. The photo on the right has some specs of bright white, which the varnish cannot (and did not) turn translucent.
My varnish plan is to do the deck and coamings first, then the hull. This is definitely backwards. What you see here is the first coat, lightly sprayed on with a Finex Mini-HVLP gun. This is on the recommendation of Royce, an Airstream Forums member and outstanding woodoworker. The Finex HVLP might have been a better choice, but I wanted to be able to spray under the coaming lip without runs. I’ll use the bigger gun on the hull.
I’ve masked off the cockpit and the hatch lips. I use a small foam brush to saturate the edges of the hatches to make sure the end grain is sealed and also do the vertical edge of the hatch opening. I have masked off the hatch lips because I want the contact cement to bond directly to the epoxy—the solvent in the contact cement would melt the varnish and possibly make for poor adhesion of the foam seal. In the photo below you can see I have taped a paper skirt all the way around the sheer so I won’t have to re-sand the hull before I start to varnish it.