There are lots of different options for clearcoating (AKA "sealing" or "finishing"). Here's what I've used and my opinion of the results:
- Water-based polyurethane: can be brushed on or sprayed on using HVLP sprayer. This is my default finish for decks. Cures hard, but usually requires 2 hours before recoating. I typically apply 4 coats for durability, and need to sand after the first due to the grain raising from the water-based composition. You can also buy spray cans, but I've had mixed results from the sprayer performance (sometimes the spray wasn't very fine and bigger drops would appear on the board).
- Water-based spar urethane: similar to polyurethane, but this doesn't seem to cure as hard as poly. Usually this is listed for "exterior" use, and polyurethane is listed for "interior" use. So, I got this because I figured a board would qualify as "exterior" use. But, boards get thrashed and many aren't meant to last years - after trying both poly and spar, I decided poly gives a harder, more desirable coating for how I use my boards.
- Minwax Polycrylic: I can't really tell a difference between this and water-based polyurethane on a board. No difference in application.
- Oil-based polyurethane: slightly more toxic / harmful to the environment than water-based poly. Yellows over time. I've used this only a few times. Supposedly it is more rugged than water-based poly. Don't need to sand after first coat since there isn't grain raise.
- Rustoleum Triple Thick Glaze: super-thick / heavy spray-on coating. Short recoat time. Very glossy. Probably a bit excessive for most boards, unless you want a really glossy and thick/heavy finish
What do you recommend? What do you suggest builders stay away from? I recommend water-based polyurethane, applied with a synthetic bristle brush or HVLP sprayer (or, use a spray can if you're just making one board and test the spray on some scrap to make sure it sprays good, first). Follow the instructions on the can of whatever you use. (I most often use Varathane, which I can get at most hardware or paint stores.)
Next: When to apply graphic?
- Test your clearcoat on some scrap wood and see if your printing/painting process works on the scrap piece. I've found Sharpie works on polyurethane better than raw wood (raw wood results in bleeding), but acrylic paints need to be applied on the raw wood (doesn't stick to clearcoat). I have successfuly spray painted onto a clearcoated board, though.
- Clearcoat as soon as possible, to prevent moisture change in the pressed board, and prevent warping.
- Apply clearcoat over a graphic helps maintain the graphic (it acts as a protective layer).
- If applying a stain, you must stain the wood before clearcoating. Stain won't penetrate the clearcoat.
- Test the application of your clearcoat on some scrap painted wood before directly applying to your graphic - if you apply the clearcoat too soon after applying a graphic or painting your board, the graphic/paint can smear. (Spraying clearcoat, rather than brushing, can help prevent this.)
- Do wood burning or laser engraving before clearcoating (clearcoat fumes may not be the greatest thing to inhale, plus you'll want to clearcoat the burned area regardless if it was already clearcoated, since the coat was burned off).
Please add your tips to this thread. This was a confusing topic for me when I first started building boards, so any advice you can share may help another builder!
