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Q.Our local lumberyard carries .40 CCA-pressure-treated wood. The label says the wood may be used for ground contact. The wood has needle marks from the treating process. When I cut the lumber, the treatment appears to be only about 1/4 inch deep, which doesn’t seem adequate for sill plates in contact with concrete. I have also used .60 PT, and it shows green all the way through when cut. However, my supplier assures me that the .40 PT will not fail from either insects or moisture. Is he right?

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 a result of incising, a process in which lumber is passed through a series of rollers equipped with teeth that sink about 1/2 inch into the wood. The incisions expose the more absorbent end grain of the wood throughout its length, allowing better penetration and chemical retention. Typically, incising is used for more difficult-to-treat species like Douglas fir (which can have more heartwood) and not southern pine.

So is your wood okay? Probably. There’s a good chance it’s heartwood, and even the shallow penetration of heartwood afforded by incising has some value. Rot fungi usually begin to grow not in the middle of the wood but on the surface. Where there are cracks or checks in the wood, incising helps reduce the likelihood that fungi can get into those pathways and rot the wood from within.