Through a process called photo degradation ultra violet uv radiation damages the wood and the finish.
Clear coat for exterior wood door.
Of the three clear exterior finishes exterior oil is by far the simplest finish to apply.
At the surface of the wood uv breaks down the glue called lignin that holds the wood fibers together.
Either by forming a hard film over wood or by penetrating it.
Application ease and service life are the two major differences between these finishes.
Exterior oil exterior varnish and an epoxy sealer with an exterior varnish topcoat.
Clear finishes work in one of two ways.
The other option is wood boat bright work and use spar varnish but realize boat coatings are made to be removed and renewed periodically so the same will happen to your door.
There are three basic clear finishes for outdoor furniture.
The finish will not hold up to the sun and weather requiring yet another refinish job.
This can cause problems if you apply the wrong type of polyurethane.
Polyurethane wood finishes are synthetic coatings that prove highly durable and water resistant making them the best clear coat for wood protection.
Depending upon exposure you are good for another two to twenty years.
Polyurethane is the most durable of clear exterior finishes.
The film forming products both classic varnishes and modern urethanes are unmatched in their ability to bring out the beauty and depth of a wood surface while guarding against wear and tear.
They provide a natural appearance with a variety of satin semi gloss and glossy sheens and are ideal for kitchen cabinets doors furniture and floors but not recommended for outdoor use.