Many professionals recommend spar varnish for wood that will be exposed to seasonal changes because spar varnish expands and shrinks with the wood rather than remaining rigid. You should recognize some things in order to get the most favorable results. Before you buy spar varnish, read through this article, and take note of the peculiarities involved with using the product.
Use a Quality Brush
First, always use a good-quality brush. A natural bristle paint brush with a chiseled edge works best for spar varnish. Synthetic bristles can introduce tiny air bubbles into the varnished surface, and bubbles result in far more work before you can complete the project.
Thin the Varnish
Use mineral spirits to thin your spar varnish five to ten percent. By creating a thinner varnish, you allow it to flow out better and cure slower. Bubbles have more time to escape. You can avoid many of the bubbles in spar varnish if you do not scrape excess varnish off, as you might do with paint. Also, be careful not to over-brush, which also introduces tiny bubbles.
Lastly, always pour some spar varnish into a dipping pan. Dipping straight out of the container creates bubbles in the can and can also introduce dust. And dust can ruin the entire can of spar varnish.