After shooting the 3rd coat of build up varnish on Gerry Santiago's console this morning I began wondering just how far I could push the Epifanes RapidClear. Epifanes recommends allowing a 5 hour drying time between coats, but this is a statement that seems to be implied to mean for brush application.
The difference between the thickness laid down with a brush and that of a spray gun with a 0.0075" tip is at least 10 times. So I set up an experiment to test spray application, building the thickness to similar that of a brush, on a vertical surface without a sag or run.
Using a scrap piece of black melamine, I sprayed a standard coat just heavy enough to be fully wet but not heavy enough to develop a run or sag. Then I set a timer for 5 minutes and shot another coat. I repeated this schedule through 10 coats successfully without any evidence of sagging. The 5 minute wait time allows the varnish enough drying time to support another coat but still wet enough to blend and not trap volatiles.
After a couple of hours of drying time I measured the difference between the unvarnished & varnished areas of the sample. That came out to be 0.004" which would probably shrink to around 0.003" at fully cured status. Initially this tells me that the 6 planned coats & spray schedule I'd planned for the console was only going to produce about 2 or 3 thousandths before sanding. The same schedule applied with a brush would yield around 9 thousandths.
So initially my spray schedule has changed from 6 coats to at least 24 coats of the RapidClear. The good news is that I can spray up to 10 coats back to back at 5 minute intervals. I already have 3 single coats, leaving 21 to go. Using Epifanes drying schedule of 5 hours between coats, I can hot shoot 7 coats each 5 hours & only increase the shoot labor by about 1/2 hour per segment.
10 coats, 5 minute intervals, 45 minutes...
Before settling with this new schedule, I'll have to test the cure after 5 hours to be sure that the additional thickness won't require more drying time. I'll post that result later...
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