Glenn Mathewson points out (in “Decay Resistance and the Code,” May/June 2014) that field treatment of cuts and holes in pressure-treated pine with copper naphthenate is not specified in AWPA (American Wood Protection Association) Standard M4. Though that’s true, both the Southern Pine Council and the AWPA note that field-treating pressure-treated southern pine is a recommended best practice. And my experience with several pressure-treated decks built between 2004 and 2009 that have shown signs of decay has convinced me that field treatment is a good idea.
In most cases, the rot occurs where cut ends are in contact with other wood, such as the butt joints of built-up beams, stair-stringer tread cuts, and joist ends at the ledger and rim joist. I’ve even found rot in ground-contact-treated 4x4 posts, where beams are resting on top of the posts.
The challenge in my area is finding copper naphthenate. Since cuts in treated wood are rarely field-treated on the East Coast, there’s little demand for the solution, and most lumberyards don’t stock it.
East Greenwich, R.I.