Treated pine vs. cedar

      The Wood Doctor offers his prognosis for outdoor projects using cedar and treated pine. 1998.

by Professor Gene Wengert

Help! I have been told, by supposed "experts"--fencing companies--that pressured pine is better than #2 Welco cedar, and that #2 Welco cedar is better than pressured pine!

I've been told that cedar will not hold up for more than 5 years (if we are lucky). That cedar runners, and not pressured pine runners should be used with cedar.

This is an expensive project, and I really do not want to make a mistake. Is there a non-biased opinion comparing the two woods? Or is there a third wood that's better than all the rest?

Properly treated southern pine lumber or posts will last for a hundred years even when in contact with the wet soil. (For above ground use, the amount of preservative required is 0.25 pounds per cubic foot. For ground contact the amount of preservative is increased to 0.40 pounds per cubic foot.

In all cases, make sure that the treating is certified with a stamp or label from the AWPB; this assures you the quality that you need. Never purchase wood without the quality label; never purchase wood that is "treated to refusal" or without the quality assurance stamp or label; there are some people who don't treat wood well (money is more important than quality.)

The heartwood of western red cedar and Alaska cedar are known to be very decay (and insect) resistant and will also last for a long time. However, the sapwood of cedar (white in color and the second growth cedar (often lighter red than normal) do not seem to possess the same level of decay resistance as the heartwood of old growth. Much of the wood in the stores today contains some sapwood, which will decay within a year or two.

I just put in a deck and used treated pine. The builder wanted to use cedar, but my feeling was that pine would be better for me. Another concern might be that by using old growth cedar we might be doing more damage to the environment than by harvesting the faster growing, more replaceable, pine. I did put in a cedar fence, however, with treated pine posts. I think the cedar has a better look as it ages, but will need occasional checking for weathering damage as the fence ages because fence boards are usually not the highest quality wood to begin with.

Also, even though the chemicals we use for treating are not entirely without environmental risk (we use copper and chromium), the fact that the wood will last for 20 times longer than untreated seems to justify their use (this is referred to as life cycle analysis). It would seem better to cut a tree once every 100 years and use the chemicals rather than to cut a tree every 5 years. Of course, this doesn't address the issue of whether I need a deck!

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.

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The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
Pine treatment is extremely toxic. The US has recently joined the group of countries that have put restrictions on where treated pine (CCA treated timber) can be used. Please ask for guidelines for using CCA treated timber from your local supplier. It is deadly to burn treated pine.

Comment from contributor B:
Unfortunately, though it was said pressure treated pine would last decades, that is not always the case. In the Pacific Northwest, it is not uncommon to have to replace treated posts in ten years, or sooner. Treatments do not go all the way through 4x4's and they tend to rot from the inside out. What likely happens is, the 4x's shrink, as they lose moisture, resulting in cracks. This leaves openings to the inner core of a post, where treatment is minimal, or has not reached at all.

To be fair, cedar posts would not fare as well as treated pine in our environment. You may be lucky to get five years out of an old growth redwood cedar post. To greatly expand the life of your posts, regardless of which you choose, keep them out of the ground, if possible. You can do this by using stirrups mounted in concrete.

An additional advantage of stirrup mounted posts is, replacement is simple. Merely cut the old boards and 2x's lose with a reciprocating saw (rather than pounding boards off, which breaks most of them). Then install the new post and reinstall everything with fresh fasteners.

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