On Nov 10, 6:32*am, Perry wrote:
I am preparing to varnish the rails thwart and deck of a newly
constructed canoe. Mahogany and Ash. Any advise on when or when not to
use a sealer first? Also, I have seen how varnish can yellow the
appearance of Ash, any advise on maintaining the white appearance of the
wood?

--
Perry

Hi Perry,

Pretty much all single part varnishes and polyurethanes have an amber
tone to them but some more than others. Varnishes that are very
traditional in composition utilize pine resins will often have the
most amber tone. Brands such as Epifanes and Le Tonkinois fall into
this category.
Two part, catalyzed urethanes can be water clear but are both
expensive and difficult to apply.
I would recommend you look at single part polyurethanes. My choice
would be Sikkens "Clear Varnish UV". I have used it many times with
great results.

Even if you find an un-tinted product, the UV exposure will eventually
give your wood an amber tone anyway. I say just go with it.

The suggestion of using epoxy as a sealer is okay if you use a product
with UV inhibitors such as West System 105 resin with 207 hardener.
Even then, varnish is still required as a top coat. Epoxies are very
prone to UV degradation and will turn milky and brittle with exposure.

Sealers are generally just thinned down versions of your top coat.
Standard practice is to thin your first coat by 25%-50% and increase
viscosity as you build coats. You can also use tung oil or linseed oil
as a sealer coat. Be sure to thin it a bit and wipe off excess oil
thoroughly. An extra day of drying may be wise if you are in a colder/
damper environment.
There is nothing wrong with just starting off with a thicker
consistency so long as you do not try to lay it on too heavily.
A round, pointed brush works really well on small rounded mouldings by
the way.

I am personally not a fan of using epoxy as a sealer but as Scotty
suggested, it can work well for your goal of keeping the ash white but
I believe it is best if you use a product with UV inhibitors such as
West System 105 resin with 207 hardener. Even then, varnish is still
required as a top coat which will still impart an amber tone.

My top picks are the traditional varnishes mentioned earlier and am
now using Le Tonkinois almost exclusively because it is non-toxic and
VOC free. http://www.tarsmell.com/letonkinois_original.html

Mark Reuten
www.nomadboatbilding.com