Spar varnish -any tips?

I recently built a couple built-in cabinets (two drawers and a door into a cavity where a refrigerator used to go) and some crotch walnut wooden panels to surface a couple interior doors. I don’t know anything about boats, but these clients seem to love the ultra high gloss spar varnish finish. I’ve been using Epiphanes and would appreciate any tips/suggestions for getting a good finish. My limited experience is that it’s super thick and the brush marks don’t really seem to level out over the recommended 24 hour driving time between coats. Should I sand between coats? What grit? What about a final polish after the surface is cured 72 hours with something like rotten stone etc.?

Thanks in advance for any advice and suggestions. I apologize for my naive question.

All the best, Mike

Spar is typically an exterior finish. It should level very well and is not typically rubbed out. A badger hair brush is often recommended. I have always used a china bristle brush with good results. I only use it for outdoor projects.

Spar varnish has UV inhibitors that help block the suns UV light from reaching the underlying wood which is one of the reasons it is used for exterior applications but this is usually not needed for interior applications. Spar varnish is composed of much longer polymer chains than regular varnish which makes it a more flexible finish which is good for boats and stuff where there is a lot of flexing but not ideal for interior applications as it is a softer finish. The long polymer chains also make spar varnish take a very long time to dry and fully cure.

My most used finish is 1/3 varnish (or spar varnish depending on the use case), 1/3 boiled linseed oil or tung oil and 1/3 turpentine with a bit of Japan dryer. I usually apply it with a small foam roller or foam brush but have also sprayed it on large projects. Because the finish is thinner each applied coat is thinner and it will take many more coats than just straight varnish. On the very first coat on a project I will often mix the batch extra thin (1/2 turpentine, 1/4 varnish, 1/4 oil) to get maximum penetration of the wood pores. I will build up several coats then sand with a fine Scotch bright before the final coat. I mix a fresh batch for the final coat as stuff tends to accumulate in the finish container over several applications. Measurements do not need to be exact, I pretty much just eyeball the proportions these days. I have never noticed any difference between the gloss of spar varnish and regular varnish. I usually use a semigloss or flat finish varnish for my projects but if the customer wants a high gloss finish a gloss varnish in the above mix should give them a high gloss finish... it is just a mater of taste and preference.

I love the above finish for any dark wood. It is my favorite finish for walnut and Ipe because it really makes the grain pop. For light wood any oil based finish will impart a pretty heavy yellow cast to the wood.

I only rub out the finish with pumice, rotten stone or similar if I want to soften the gloss. For a high gloss finish I would not rub out the finish after the last coat.

A spar varnish surface may be usable after 72 hours but it certainly won't be fully cured, in my experience, even with the addition of the Japan dryer. Regular varnish usually cures faster than spar varnish and usually cures to a harder finish.

It sounds like you may be a pro in which case the above finish might be to time consuming to be practical for your uses.

As Michael says (I forgot to mention) sand between coats with 220 or finer. I use polyurethane for in-place cabinets and trim. Learning to apply it and keep a wet edge without runs and drips is an on going challenge. I remove doors, drawers, and any components that can be laid flat and spray when possible. I have only had a few clients request gloss. It does "Pop" and earn its title "Bright Work"

I use a Badger brush, and clean with thinner followed by acetone directly after each coat (see my old thread in the link below), being careful to not let the acetone get up under the ferrrule where the bristles are glued in. It's important to get the brush completely clean to be able to put on smooth coats.

Total Boat makes one that dries really fast between coats, which lets you put multiple coats on in one day. I used to use Epiphanes too, but this one seems as good so far, and the job can be finished days quicker.

I sand after the first coat, and maybe before the last, but more than that is really not needed.

Spar Varnish and Marine Varnish are pretty much the same thing, but Spar is more flexible. Marine Varnish is a harder, and more durable finish. I don't see any advantage to using Spar on a non-flexing anything.

https://sawmillcreek.org/showthread....ght=total+boat

Another issue with spar varnish, perhaps related to the long drying time, is it will off gas for weeks or months. Not an issue when used outdoors but can be a problem for indoor projects. I used spar varnish on a driftwood bed over a decade ago and recall it took over a month before it was odor free.

Thanks Guys- super helpful!