I just had my pressure treated deck is cleaned and it’s still green in some spots, WHY?
When pressure treated decks are cleaned properly, all the mold and mildew will be removed, however, you may still see some green in the wood. Why?
Pressure treated wood also know as green wood is treated with a variety of chemicals to give it an increased resistance to moisture, fungus and wood eating insects. Some of these chemicals are water based and some are oil based. (They all change the color of the grain). This type of protection makes the wood heaver and easily identifiable.
So, when you see green in wood it’s not always mold. Below are some of the most common types of chemicals use in treating pressure treated wood.
Chromated Copper Arsenate (CCA)
o CCA was once the most common chemical used in pressure treating. It contains chromium, copper and arsenic and turns the wood dark green. CCA protects against decay, fungi and wood-boring insects but is also poisonous to humans and listed by the State of California as a carcinogen. Since 2004, the lumber industry, under pressure from the Environmental Protection Agency (EPA), discontinued its use for residential lumber. It is still used for industrial purposes such as pole, pilings and bridge timbers and is still the best preservative there is, according to the Natural Handyman.
Alkaline Copper Quat (ACQ)
o ACQ contains copper and a quaternary ammonium compound, hence it is commonly called quat. It less toxic than CCA and has replaced it as the most common pressure treatment for residential use. There are two kinds of quat commonly used, AQC-B and AQC-D. The former is formulated with ammoniacal copper and turns the wood a dark greenish-brown color. The latter uses amine copper and turns the wood lightish-brown. Both chemicals can penetrate difficult-to-treat species like Douglas Fir and are primarily used on the West Coast. ACQ protects wood against rot and insects, but unlike CCA, is unsuitable for underwater use.
Copper Azole (CBA)
o CBA is another copper amine product that has been developed for residential use. It contains copper and tebuconazole and may also contain a little boric acid. It protects against rot and insects, but like ACQ, is unsuitable for marine use. It does not penetrate as readily as ACQ, and ammonia is sometimes added during the treatment to improve penetration. CBA turns the wood light brown