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Protect Exterior Wood with Epoxy and Spar Varnish

Preserve natural wood furniture and trim and protect it from water and UV damage with a classic boat-builder's finish.

by Eric Smith

From The Family Handyman

If you'd like to preserve the natural wood appearance of your wood entry door or your outdoor furniture, take a lesson from boat builders. Boat builders and restorers use multiple coats of epoxy and spar varnish to protect wood - instead of spar varnish alone - because the combination is much stronger than either finish is separately. Epoxy creates a tough, flexible moisture barrier; spar varnish adds depth and UV protection, which keeps the epoxy from yellowing and eventually disintegrating.

The epoxy, a special type for clear-coating wood, is sold at woodworking suppliers, hobby shops and marine supply stores (see Buyer's Guide). It's expensive - the 2 quarts we used for our project cost $70 - but when fully cured, the finish is very tough and will last for years.

Two-part epoxy

Click Image to enlarge.
Mix the resin and hardener thoroughly in a clean, disposable container, in the proportions specified by the manufacturer.

To begin, sand and clean the wood, then stain it if desired. Mix the resin and hardener thoroughly in a disposable container. A batch will start to harden in about 30 minutes, faster if it's hot out, so just mix a small quantity the first time to see how far you get. Apply the epoxy with an inexpensive natural-bristle brush (Photo 1). (You'll need a new brush for each coat.) When the epoxy in the container starts to stiffen and feel warm, discard the container and the brush and mix a new batch.

Allow the epoxy finish to harden overnight, then sand thoroughly and apply another coat. The manufacturer recommends three coats.

Sand the final coat of epoxy after it has cured for at least 24 hours (Photo 2), then vacuum the surface and wipe it with a damp rag. Topcoat the epoxy with a minimum of three coats of exterior spar varnish (Photo 3). Add coats of varnish every few years to keep the finish looking fresh.

Click Image to enlarge.
1. Spread the epoxy, then lightly drag the brush back through to even it out and eliminate bubbles. Work quickly and allow the thick epoxy to flatten without brushing it too much.

2. Sand each coat with 120-grit sandpaper to flatten out any ridges and flaws, then clean and resand with 220-grit to create a smooth, scratch-free surface for the varnish.

Click Image to enlarge.
3. Apply three coats of oil-based spar varnish with a high-quality chinabristle brush, brushing with the grain. Sand the varnish between coats.

Buyer's Guide
You can find epoxy for clear-coating wood at local distributors or order online at:

www.systemthree.com: (800) 333-5514

www.westsystem.com: (866) 937-8797

From The Family Handyman - April 2007