Ive put a mahogony glass on on a resin tint PU longboard, and I put some marine varnish over the fin that I have left over from the rowing boat that ive just built. I taped off the bottom of the board whilst i was applying the varnish but in lifting the tape a little early to check how it looked against the sanded finish, I realised a bit of the varnish got under the tape, when i tried to pull it off with my finger, it ended up looking really nice and shiny over the grey resin tint area. Im wanting to apply to varnish over the whole board now, it had a gloss coat, but I havnt sanded it all the way down or polished it because iv never done a polish before, truth be told, i dont even have a polishing mop. Is it possible to put marine varnish all over a board, has anyone had any good results doing this? Part of the resin tint is white, so thats another thing im nervous about, as the marine varnish is definitely not white. Anyone got any advice or thoughts for me?
Its standard for a lot of boat builders to do 3 or so coats of clear epoxy and then top coat that with marine varnish and it look killer. the problem is when you do that finsh over white (foam or whatever) over time it don’t look so good. I prefer to do clear epoxy and then spray on several coats of 2 pack Automotive clear coats. The colors underneath stay clear because 2 pack is clear. Marine varnish is amber ! So no don’t use the Marine varnish.
I spent years painting and varnishing all types of boats from 8" to over a 120 foot Yachts. A
traditional marine varnish on teak or mahogany looks great. The deep rich light amber color is classic. 6 or so coats on a Teak hand rail sanded to at least 220 between coats makes an ordinary run of the mill 30" sloop look like gem.
If you plan this to be a show board then it might be worth the effort. If you plan to ride it and use it I would go with a diffrent finish. varnish is rather soft and plyable. it moves and breathes with the wood. Keeping varnish looking good is a lot of work.
Wood Ogre has it right there are better solutions for your board.
If it’s old-fahsioned spar varnish it will be soft and yellow and will never last.
If it’s a modern polyurethane it will be hard and fairly durable and it might even be clear instead of yellow.
In “marine varnish” there is a huge range in between those two extremes.
When I was making a lot of wooden kiteboards to sell, I used to use a waterbourne polyurethane over the epoxy to protect it from uv and make the finishing much faster and easier. I scuffed the finish with a scotchbrite pad to get out the bits of dust that invariably landed in the finish in my dirty shop (no seperate sanding room). But the poly was very clear and hard and my boards really sparkled once you got them wet.
The stuff I was using was not “marine grade” I recall that it was made by General Finishes in New Berlin, WI (near my home town). I can’t remember for sure but it might not have even been “exterior grade” It still lasted at least as long as the boards did - it’s not like you board is sitting in the water 24-7.
I’ve used interior grades many times and their usually fine for boards. They’ll actually begin to turn white if left wet for any length of time but will turn back clear when they dry out. I’ve never seen an exterior grade that didn’t have some yellow to it.
Varathane Spar Urethane - water-based is the best I have found. This is very close to clear and does not yellow. Others I have tried (especially Minwax) look like they have received a suntan before they ever leave the shop. The finish holds up very well using three coats.