Expert: Richard Taylor, AIA - 11/30/2007

Question
Richard,
I read an answer you gave around NOT sealing a deck that has fungus growth. I too have a deck that is in the shade in PA. The guy who built it told me that I had to seal the deck. Being in the shade and being in a the snow belt, it would have moisture sitting on it all the time (Its not really possible for me to keep this deck dry). Should I seal it ?
Also you mentioned cleaning with a fungicide. I have a particularly ugly black fungus which grows on the deck. Is there one time of year that is best to apply the fungus (i.e in the spring before it starts, mid summer while its growing or in the fall when its done).

Answer
Brad - thanks for your question!

The problem with sealing is that it eliminates a path for moisture to escape the wood.  It's a short-term solution.  The wood's going to get wet - nothing you can do about that - so you need to make it easy for the wood to dry out again.

That means plenty of air circulation over, under, and around the deck, and keeping the wood uncovered and unsealed so that the moisture can escape.  Sealing it would accelerate the damage from moisture by holding it in the wood longer.

The fungus you're concerned about needs warmth, wood, and water to grow.  Keep the wood dry and clean will help control it; killing the fungus with a proper deck cleaner on a regular basis should keep it away.  Use the fungicide when the weather starts warming up, but otherwise just follow the manufacturer's directions.

Hope this helps!

Richard Taylor, AIA
www.rtastudio.com
www.rtaplans.com