A. Contributing editor Paul Fisette responds: How deeply the chemicals penetrate the wood during treatment is indeed important. Penetration levels vary widely. Heartwood is more difficult than sapwood to treat. The heartwood of Douglas fir and southern pine (both commonly used for pressure treatment) resists penetration and may allow only 1/4 inch of chemical penetration. So if the lumber you purchased was heartwood, it is not surprising that you would see shallow penetration. The good news is that the heartwood is typically more rot resistant than the sapwood. The heartwood of both Douglas fir and southern pine is considered moderately decay resistant, but virtually all treated southern pine is second-growth, easy-to-treat sapwood.
The amount of chemical retained by the wood is important. The 0.40 designation of the wood you bought means that the amount of chemical retained by the wood after treatment (its retention level) is roughly equal to 0.40 pounds of chemical per cubic foot of wood. That is the correct amount for “ground contact.” The “needle marks” that you see are...
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