Pressure
Treated Decks built in 2004 and beyond– The New Deck Failure Problem
Due to pressure from the EPA,
CPSC, consumer advocacy groups, and others pressure treated wood manufacturers voluntarily agreed to stop using chemicals
including Chromate Copper Arsenate (CCA), Ammoniacal Copper Arsenate (ACA), and
Ammoniacal Copper Zinc Arsenate(ACZA)
to preserve the wood used in residential exterior construction, including decks, playgrounds, etc. effective December 31,
2003.
Most pressure treated lumber
manufacturers have changed over to a new chemical known as “ACQ” or alkaline copper quaternary compounds as a
preservative. This new pressure treating poses a problem with fasteners and flashing. Flashing is typically an aluminum metal material with a purpose of directing rain
water away from the home to prevent deterioration of the framing. The fasteners
are metal bolts, screws and/or nails used to secure the deck to the home and/or hold the deck together.
The problem is you end up with
two metal compounds in direct contact with each other in an exterior application so water contact is going to happen. When two metals in direct contact with each other are surrounded by an electrolyte
(water) rapid corrosion of the metal on the lower end of the electromotive series will occur.
Simply stated this means that
the aluminum flashing will rapidly corrode and lead to a water intrusion problem inside the framing of the home. Also, if the fasteners and nails are not made from the manufacturers approved materials they too will corrode
and the deck itself will fail.
Below are links to some
of the main manufacturers of “ACQ” alkaline copper quaternary compounds and their printed statements regarding
fasteners.
