Chris Neurath sent this long note that is important enough to run in the column. (The column appeared in the Observer on Jan. 26.)
“You may have given bad advice that leads to safety issues when you said not to worry about deck joist hangers that were ‘rusting a lot.’ (question from Arthur, chat room)
“Here are my comments: Have you read the tiny print on today’s generation of joist hangers and other hardware meant to be used with pressure-treated lumber? They all warn that the current generation of treatment chemicals, which is usually ACQ (Ammonia Copper Quarternary) is more corrosive than the previous generation, which was ACC (Arsenic Copper Chromium). The ACC was phased out by manufacturers about 15 years ago because of the toxicity issue. It was loaded with arsenic and chromium.
“Most of the current generation of pressure-treated wood is more corrosive and all hardware warranties (including for joist hangers) require that only specially coated hardware designed to withstand contact with ACQ may be used. Mostly they use thicker layers of hot dip galvanizing, but some hardware is stainless steel for even better corrosion resistance.
“It is quite possible that Arthur’s deck is made from ACQ lumber but that pre-ACQ hardware was used. It took 5 or 10 years for manufacturers to realize the ACQ was causing premature corrosion of hardware and for them to develop and distribute the more corrosion-resistant products.
“Your suggestion to only worry if the deck starts shaking or sagging does not seem very safe. Catastrophic deck collapses have occurred, typically happening when there is a party with a lot of people on the deck.
“Although Arthur noticed the joist hanger itself rusting, it is possible the nails are even worse but less obvious. Joist hangers require specific nails and for ACQ lumber they need to meet the current corrosion-resistance standards. Unwitting builders, probably even now, might not have bothered to use nails approved for joist hangers. From my own experience, I have been amazed at how quickly ordinary metal hardware and nails can corrode when used with ACQ wood.
“Please read up on this issue and warn people instead of giving them false reassurances that they don’t need to worry. One source I found is http://woodworking.about.com/od/safetyfirst/p/SafeACQLumber.htm
Thank you, Chris. Duly noted and stored in the archives.
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