Name:   lumberdude - Subject:   FYI: Pressure Treated Lumber Date:   6/13/2016 5:11:11 PM

Hello- new member, and also a long-time worker in the treated lumber business. Here are some observations that might be of some use in planning your building projects involving treated wood. Again, just my personal opinion based on a lot of years being around the product:

• The 'old' treated lumber preservative was used from the 1930s through the early 2000's. While arsenic got all of the attention, it was used only in levels that were below normal naturally-occuring levels as defined by most states. The Clinton EPA left a little booby trap for the Bush folks in the form of exponentially higher detection thresholds, which in turn set the stage for class action lawsuits. In response, the old chemical was phased out, and it was replaced by a variety of new chemicals. While the old chemical was pretty much a standard formulation, the new ones vary in their composition.
• The new preservative mixes do not contain as much copper, which gave treated lumber its greenish tint. That tint also served to cover mold and fungus which may have started to grow on the lumber prior to treating. What that means is that you are more likely to see dark mold residue on treated lumber today, even if it is no longer growing.
• Some of the new mixes have had problems properly adhering to the wood cells. Alongside this, the extra margin of preservative engineered into the chemical has been slowly but steadily reduced in response to pressure from large retailers to 'cheapen up' the product. These two things have combined to make pressure treated lumber have a shorter life than it did 15+ years ago.
• The move to all ground contact is a response to the point listed above. While the old chemical had two levels of retention, 'ground contact' and  'above ground only' (.40 and .25 to you old hands), the above ground would work in many cases where there was minimal ground contact. That is not the case with the new stuff. Two of the three major chemical manufacturers have had issues with shortened lifespans in their above ground chemical, and the move to all ground contact is mainly an effort to get more chemical into the wood.
•  The preservative composition is between 98-99% water, so it is still pretty wet when it goes to the retailer. The preservative has no effect on the movement of the lumber; it only keeps it from rotting. Get it fastened down before it dries, then give it at least a few weeks (in the summer) to dry out. After it dries, put a sealer on it, and plan on redoing this as a maintenance item every few years. The goal is to minimize water going into and drying back out of the wood. It-the water- has the same effect as bending a coat hanger back and forth until it breaks. In this case, the movement results in warping, twisting, cupping, and splintering. This is a natural thing for pine wood, but you can minimize it with a sealer.
• Some sealer manufacturers do more marketing than others- I don't know if there is that much difference in performance. That question might be better answered by a painter. The point is, be ready to do some sealer work to keep your deck, dock, or pier in good shape.

Kind of long, but hopefully some of this will be helpful with your projects.