View Full Version : Thinning Spar

Roger Bell
08-17-2005, 10:58 PM
Is there any reason why common Spar Varnish cannot be thinned (with spirits or naptha) to make it into a "wiping" spar the way that furniture varnishes can be?

Manufacturer says do not thin by more than 10%. If this is so, why is it so?

Jim Becker
08-18-2005, 9:22 AM
Government (VOC - Volatile Organic....something or other) rules are why you are seeing the "no more than 10%" statement on the can. Restrictions on solvent-based finishes are getting stronger all the time. You should be able to thin your finish for wiping with no problem. (Do remember that spar varnish is designed to be a flexible finish...spars bend...so don't assume it's a "hard" or "strong" finish. It's not.)

Howard Acheson
08-18-2005, 5:49 PM
Following along Jim's line of thought, why are you considering using a "spar" varnish? Is this an outdoor item?

In general, interior varnishes and poly varnishes are harder and more durable than exterior varnishes.

Roger Bell
08-18-2005, 9:52 PM
Thanks guys. I am inquiring for a friend's project. A white oak church pew that he intends to use on an outside partially covered (roofed) porch. He has tried brushing full strength with such disastrous results and has had to sand it down and start over. I have suggested the more fool proof wiping method.....a diluted mix with more coats with the advantage of more predictable results. He called MinWax and they tried to discourage him from diluting more than 10%. I know good and well you can thin it, but wanted an idea of why they might have said what they said. Helmsman Spar is what he wants to use.

Howard Acheson
08-21-2005, 4:22 PM
>> Helmsman Spar is what he wants to use.

I would suggest you might want to do him a favor. As Jim has said, spar varnish is a finish designed to be soft and flexible. It is not a good choice for something like a pew that will be sat on or otherwise subjected to abrasion. Second, Minwax Helmsman was the first clear finish to fail a few years ago during Consumer Report's long term testing of outdoor and deck finishing materials. It lasted less than a year. It's a poor product.

If your friend wants a longer lasting product, suggest a real marine exterior varnish (not a spar varnish). It can be purchased and a marina or marine supply store. Look for a manufacturer like Wolsey, Interlux, Pettit or Epifames. They are not cheap but they last the longest. Be sure to follow the directions regarding number of coats. It takes a thick film finish for the UV inhibitors to works correctly.

Steve Schoene
08-22-2005, 11:45 PM
I want to second Howard's suggestion that real marine varnish is MUCH more durable than stuff labeled "Spar" Vannish at paint stores or big boxes.

These high quality varnishes brush more easily than cheapo stuff too, though they all (especially Epithanes) need a small amount of thinner to help them flow out. I just don't see the advantage of turning it into a wiping varnish, which doubles (at least) the number of coats needed. Brushing on a good varnish should be a learnable task.

It needs a good brush--it should have tapered natural bristle, with flagged tips (split ends), have a chisel tip (the bristles in the center of the brush are longer than those on the outside) I like a 2" or 2 1/2" width.

After as much dust control and removal as you can, brush on the varnish. Method is not critical here, but I like to work cross grain to spread the varnish, and then brush it out evenly with the grain. The final brushing should be "tipping off", which is very light passes with the almost dry brush held vertically with the intent of evening out any heavy or thin spots. On large surfaces you have to work fast enough so that the full surface can be tipped off while the varnish is still wet. GOOD LIGHT, with a raking angle is an aid in avoiding skips. IF YOU NOTICE A SKIP after the varnish start to set up, ignore it until the next coat.

VARNISH ALWAYS LOOKS LIKE ______when it hardens because unless you work in "clean room" conditions there WILL be dust nibs and other glitches. Between coats remove runs and sags with a scraper, and either LIGHTLY sand the surface with 320 grip or very lightly use a scraper to knock down the nibs.

After the last coat has cured, which should be as perfect as you can make it, after the sanding/scraping to remove dusts and defects, you need to rub out the finish. Give the finish at least a week before rubbing out. This should be about the same as rubbing out after the dozen or so wiped on coats had you chosen that method of application.