I have some projects coming up for the garden and I want to use some screws with the raised beds. I recently was told certain screws get 'eaten' by the chemical used for treating the lumber. If this is true, what screws will last longest with the treated lumber?
Pressure treated lumber is treated with Alkaline Copper Quaternary (ACQ), an environmentally friendly water-based preservative that is free of arsenic and chromium. However, ACQ treated lumber is more corrosive to metal, so the right fastener is key to a safe, long lasting deck, fence or other outdoor project.
When nails are exposed to ACQ, a chemical reaction occurs, which accelerates the corrosion rate of the fastener. In addition, the organic components of ACQ attract water, further increasing corrosion on the fastener.
The wood treatment industry recognizes the corrosive nature of ACQ in relation to fastening systems, and recommends hot dipped galvanized or stainless steel nails be used. Hot dipped galvanized nails must meet American Society for Testing and Materials (ASTM) A153 Class D standards and stainless steel nails should be made from grade 304 or 316, to provide maximum corrosion protection. If screws are used they must be rated for ACQ.
Galvanized and coated deck screws rust in treated pine; I am sure it has very little to do with the treatment. The first screws failed at about 10 years but a few lasted 20 years. I expect the stainless replacements to last much longer; The box indicates they are 316 SS which is likely true. Driving the heads down into the wood makes it worse because the recess retains water. I looked at the reference regarding corrosion and it listed no source for the corrosion reference, so I still doubt it. However I built my deck in 1996 so used CCA wood ; The EPA did not require the new crap until 2003. I am/ was a NACE certified Corrosion Specialist ( # 1635 , I have not renewed my certification) so I am not impressed by random articles regarding corrosion.