Treated Lumber vs Teak

[LaughingWarrior]

As a carpenter and home builder, I can relate a few issues with generic, Home Depot type treated lumber.

Firstly as stated above, it will absolutely destroy fasteners of incorrect type. You must use hot-dipped galvanized (not electro-galvanized), coated, or high-grade stainless steel fasteners, rated for ACQ contact. A common 16D steel nail embedded in ACQ will begin to seriously rust within weeks, and a common zinc-plated construction screw shortly after. Even hardened Grade 8 steel bolts will rust badly within a year.

Secondly, the usual stuff is either not kiln dried, or comes out of the kiln and into the treatment process. All dimensions of this stuff will shrink, crack, check, warp, twist, crown, crook and bow with extreme prejudice when exposed to sun and weather, right from 3/4" fence boards up to 6"x6" posts.

The act of fitting and fastening it, such as in a fence or sundeck for example, is often enough to (mostly) prevent this if working quickly and surely, but any surplus left in the weather for more than a day or so is typically so bent as to be useless. Even then, wide flat boards like fence boards or 5/4" radius-edged deck boards will cup and shrink, even with 2 screws every 12". Boards set flush and with edges touching will be cupped and have a gap of 1/8" or more within about 2 weeks of dry weather.

This is discouraging when you finish something like a B-E-A-utiful deck and pergola, only to see it looking years old within a month.

There are some products available which are kiln dried after treatment, which perform somewhat better in this regard, but you need to purchase them specifically, and are more costly of course. These may be a special order at your local lumber yard.

Also as stated, there are different grades of treatment. Standard ACQ is intended for exposure to weather only (with the ability to drain/dry). PWF (for Pressure-treated Wood Foundation) is incised (tiny cuts in the surface) and infused with a uniform amount of treatment from face to core, and is intended for direct, constant contact with ground. This is the material I most commonly see used on marina docks etc.

If I had to use softwood lumber on a boat, I'd choose seasoned clear pine (some might call this project-grade or cabinet-grade material) or cedar/redwood, and seal it well.

[Briney Bug]

We've built two significant cruising boats using pressure treated pine. One is a 37 foot cutter, over 20 years old and still going strong. Our current 34 foot, sail-assisted trawler is over 12 years old and still going strong. Mostly it is building the boat, or parts for a boat, using good, well tested, dimensioned-lumber techniques that often makes a big difference in longevity. I've found that contemporary-material building techniques and materials do not mix well with dimensioned-lumber, but the old, traditional techniques and materials do, things like oil based seam compounds, oil based bedding compounds, oil based paints and true varnishes, cotton caulking. With pressure treated lumber, the type of material that the fasteners are made from can be important, so it is best to do some research in this area.
Rudy Sechez

[Mike Banks]

It is not just the arsenic. The baddie is the chrome salts used as a fixative.

CCA treatment is wonderful at combating rot, BUT if one is in a situation where skin or other abrading contact is to be made with it, it needs to be fixed with epoxy resin or some tough two-pot polyurethane varnish.

Who needs the tiniest particles of dislodged carcinogenic chromium compounds in their lungs--as well as arsenic--?

The modern version has no chromium in it, I am not sure about the arsenic, so it is safer, but it does not resist rot as well as the older version when used for ground-contact applications, and termites DO eat it, even if they spit it out a lot..

[Fence Man]

Originally Posted by Mike Banks

It is not just the arsenic. The baddie is the chrome salts used as a fixative.

CCA treatment is wonderful at combating rot, BUT if one is in a situation where skin or other abrading contact is to be made with it, it needs to be fixed with epoxy resin or some tough two-pot polyurethane varnish.

Who needs the tiniest particles of dislodged carcinogenic chromium compounds in their lungs--as well as arsenic--?

The modern version has no chromium in it, I am not sure about the arsenic, so it is safer, but it does not resist rot as well as the older version when used for ground-contact applications, and termites DO eat it, even if they spit it out a lot..

This can't be repeated enough! CCA is still approved for most agricultural products in the US, so I'm around it more than I like. I really regret all of the miles of fence I built without gloves or lung protection when cutting it. What a bonehead.