A sealer is clear and stops water. A stain carries pigment and stops water and ultraviolet. In Georgia the second one matters, because sun does more visible damage here than rain.
What sealer does
Waterproofs without changing the colour, which suits a new deck where you want the timber to weather naturally. It also needs redoing more often, because there is no pigment shielding the surface.
What stain does
The pigment is the sunblock. More pigment means longer protection and less visible grain, which is the trade you are making when you choose between transparent, semi-transparent and solid.
The test for when
Splash water on the deck. If it beads, the finish is working. If it soaks in and darkens the timber, the finish has gone and the wood is taking water.
Do it in a few places. Rails and the south-facing edge fail before the middle of the floor.
New timber has to wait
Pressure-treated wood arrives wet and will not take a finish until it dries — usually a few months. Staining too early gives a coat that peels within a year and has to be stripped.
How often
Every two to three years here, sooner on a deck in full sun. Deck staining covers the work, and how often to stain a deck goes into the timing. Finished work is on our Facebook page.
