varnishing tips?

Brad C

Enthusiastic about Wooden Canoes
I am repairing an Old Town canoe for a friend and am looking for some tips on varnishing. I have sanded and oiled the hull with a 50/50 mix of boiled linseed oil and turpentine. I am going to varnish with Z-Spar Captains varnish and want to know if the first few coates should be thinned? With what? The direction for the varnish said not to unless it is required for spraying. I have heard of some builders thinning the varnish so it would strike in and as more coates are applied the ratio works its way to straight varnish.
Does any consideration need to be taken so the varnish will adhere to the oiled wood?
Any input would be appreciated.
Brad C
Hi Brad,

Captain's is a nice varnish; you've done well to choose a traditional spar varnish as opposed to a urethane varnish. Thin first coat 1:1 with a good quality thinner (you might want to use the manufacturer's proprietary thinner just to be sure there are no incompatibilities...greater cost than mineral spirits or turpentine, but it's not much additional over everything else you spend on restoration). Some people advocate going through a whole range of stepped concentrations up to 100% varnish, but this seems overkill to me. You can certainly get a great finish, excellent adhesion, and fast build by going 1:1, then 3:1 (75% varnish), and then subsequent coats at 100%. Others may disagree, but many boats finished this way give fine service with no apparent ill effects.

Number of coats? Some builders have put as few as 2-3 coats on new wood, but this is pretty thin. Old wood also may require more, though your application of oil should reduce absorption of thinned varnish into the wood. For a user canoe, you might put on 3-5 coats on top of the oil; many deep rich show finishes on old boats have many more coats.

You may use either a good quality natural brush (badger, China bristle, etc), or a foam brush. Foam will generally give you a thinner application, but they work well and don't require careful cleaning. A high quality natural bristle brush just feels good and gives beautiful application, but only practice will give you a consistently level application. In either case, flow on the varnish without excessive brushing out. Make sure you get an even coat- watch for sags and runs with a bright light at a low angle to the surface and correct them before the varnish begins to set up.

If you want an excellent book on finishing, including thorough explanation of a variety of issues and techniques plus beautiful inspirational photos, look for Brightwork by Rebecca Whitman.

May your future be glossy and resilient,
Michael's advice is pretyy much spot-on. The only thing I do differently is to thin the varnish for coats 3-5 somewhere about 5-10% - I feel it brushes out a little better and tends to sag less. I sand between coats with a 220g sanding star, available from Woodcraft.

Dan, on the road in Buffalo
What they said.

All varnishes in the last few years were reformulated to comply with new VOC regulations. The result for spar varnish is that it has become very thick and doesn't flow well (for me, at any rate) if I don't thin it at least 10%, even for the top coat (I use Man O War.). I like odorless (it's not!) mineral spirits better than turpentine as it does not retard drying as much. You can tell if it's flowing well when you brush it on, if it's sticky, you have to thin it until it flows well. Same for oil-based paints. Manufacturers are prohibited by the above rules from explaining this, but talk to a good, local, professional painter.

Everything said is is good advice. I've noticed the same thing about good spar varnish. lnstead of using a traditional solvent I've found that Penetrol, sold in most good paint stores, added in small quantities makes the finish flow better and lay out nicely. It's also great to use in the color coats over the filler. It works especially well with Kirby paints.
Thanks for all the good advice from all of you. It's has to warm up before varnishing, but i'll be ready for it. Thanks again
Brad C