“No worry” performance in ACQ and CA pressure treated lumber.
Since January 1, 2004 all pressure treated wood sold in the USA has been produced using either ACQ (Alkaline Copper Quaternary) or CA (Copper Azole) arsenic free treatments.
These newer treatments are about 6 times higher in copper content than the old CCA (Copper Chromated Arsenic). Both of the new treatments severely corrode and damage fasteners made of metals “less noble” than copper (see chart below).
Studies show the newer preservatives will destroy fasteners made of aluminum, plain steel and galvanized steel products. Even hot dipped galvanizing, a zinc coating, will fail in time. This affects not only the appearance of the fasteners but will severely compromise the long term soundness of the structure.
Fasteners made of the “300” series stainless steels, such as; 302, 302HQ, 303, 304, 305 (18-8 types) and 316 should be used in the newer pressure treated wood products.