About 18 months ago, we built a deck and a front porch on an old farm style houses here on Long Island, NY. The job looked beautiful, the clients were very happy.
The posts for the railings are made of CCA 4x4s, wrapped with “trimboard”. Trimboard is a 1x finger joint, factory primed pine board, which we use for all kinds of exterior trim applications, with no problems. The posts were painted with acrylic house paint. After last winter, the wrapping on some of the posts started showing some mold – real black patches of almost soot like stuff. About a month ago, the painter cleaned and repainted the posts, but now the patches are starting to come back! The posts wrappings are capped at the top and have a 3″ base at the bottom (both cedar). The wrapping does not touch the decking – it’s about 1/4″ off the deck.No other piece of trim we used (same material) exhibits this behaviour – only the posts.
What is causing the mold? How can I stop it? Any suggestion will be greatly appreciated.
Kroozer
I’d rather be riding!
Edited 9/19/2003 3:55:38 PM ET by Kroozer
Edited 9/23/2003 3:42:18 PM ET by Kroozer
Replies
Kroozer,
That pic is HUGE. It'll take me ten minutes to download on the dial-up. Could ya resize to somewhere around 100 kb and post again?
Without looking a the pic, it sounds like we might be talkin' about simple old mildew. I think about the best you can do is kill it off with a bleach water solution and repaint with fungicide additive in the paint. Then cross your fingers. Or did your painter already do the bleach job on it and use the fungicide?
Around here, shady side of buildings, fences, etc. are more susceptable than those on the sunny side of life. Mildew needs moisture and a food source. Did you happen to use an oil-based product on this and if so, did your painter add any linseed oil to it? Mildew loves linseed oil.
I see you're not getting many answers. I hoped you'd get some better wisdom than mine. I saw the photo before it was deleted and you do beautiful work.
Woods are classified according to decay resistance, and unfortunately, pine is in the most decay-prone group.
My suspicion is that the CCA posts still had a lot of moisture in them. They are usually stored outside in lumber yards and are not kiln dried. My first guess is that moisture from the posts is keeping the pine constantly damp from within. If this is so, then ventilating the inside with some holes top and bottom may help.
I know for certain the mold has to be killed before any further action is taken, and a bleach/water mix, fairly strong, is effective. With minimal scrubbing, this mixture will kill and remove any mold it contacts.
As to how to prevent it's return, I'm less certain. I'd consider treating the material with a good soaking coat of a preservative like Woodlife after the wood is thoroughly dry. I don't know how effectively it will soak in through the paint, but it will suck up in the end grain and your joints fairly well. Then repainting with a mildew resistant paint. If there is mold on the back side of the trim this may not work. Maybe the post trim would need to be replaced with a paintable synthetic trim.
Wayne,
You could be right about the CCA 4x4s being wet, but they sat unwrapped for quite some time (a few weeks). Maybe that was not enough, though. I did clean them last week with a bleach and water mixture, and now they look clean. We'll see how long they last!