We would pre-paint the whole board before putting the mask down with one coat of primer and one top coat. It could be any color, cause it was gonna get painted 4 or 5 more times. Let that dry for a few days. Blast it. Remove whatever mask could be removed and paint those areas. We generally lifted before completely dry also, so it didn't lift paint. Never had edges pile up on us, that I remember. By the time we got to the final lettering, border or other incidentals, we had several coats on there. The lettering always came last and many many times, we used a roller for that. Went back in and touched up with a brush if need be. If it was being gilded, we'd powder it, then size it with tinted size and gilded the next day. Always used regular size, never that 'Quick Size' crap. Ya never get the punch like you do with regular size.
We did literally hundreds and hundreds of redwood sandblasted signs back in the 80's & 90's. We were well known for our redwood signs and they lasted for years. Somewhere, I have some start to finish pictures I took back in the 80's of blasting one or two of them. We always glued up our own boards and I would personally go and pick out like $6,000 or more worth of vertical grain all clear heart 8 quarter stock. Wanted to make sure I got the grain I wanted and no cracks in the ends. We generally got 20' long pieces. We were very particular which way the grain ran when gluing up. Nothing worse, than seeing a totally new board start because someone couldn't match grains correctly. Vertical grain is beautiful and when done right, just has an elegant look about it. To me, these were the Cadillacs of signs.
I know a lotta guys today are using latex paints on these things, but I guess I'm just old school and like the brilliance and longevity from the oil-based paints.... especailly the old leaded paints....
which are still available