Pressure-treated wood

[radhak]

Just browsing at LJs, and found this nice project.

Thought I'd ask y'all - isn't pressure-treated wood really treated with chemicals, even poisonous chemicals? Is it a good (safe) material for such benches and tables which might be used by kids, or for picnics?

[docrowan]

I've done a lot of study on this. The previous chemical used was CCA - Copper Chromate Arsenic. The arsenic was a concern, although to the best of my knowledge there were never any credible studies done that showed anyone was actually harmed by it. The new stuff is ACQ - Ammonium Copper Quartenary. Ammonium "quat's" as a class of chemicals are used in a number of different applications including as disinfectants in food service. Copper is used in drinking water pipes. I'm personally satisfied there is no danger to my family from the new stuff, but I'd encourage you to do your own research. Of course all the manufacturers have whole staffs of lawyers so I had to do quite a bit of study to come to that determination, sorting through all the weasel words.

I've seen some gardening websites that advised not to use treated wood, even ACQ. I believe the advisors were too lazy to do their homework and gave the easy answer. Sort of like the old story about the housewife cutting the ends off the roast because that's the way her mother and grandmother did it. Turned out the grandmother didn't have an oven wide enough to fit a family size roast so that's why she did it, but she didn't know why the other two with nice, big, newer ovens were doing it.

Note, the kinds of preservatives used before CCA WERE toxic. CCA was developed as a kinder, gentler preservative. CCA treated wood is still available to professionals, but only in very specific applications. You won't find any at the local big box store. I still check the tag to make sure that it says ACQ on it, though.

Hope that helps some.

[radhak]

Thanks Chris, that does help a lot.

I picked up a pamplet at HD from one of the manufacturers. They do use ACQ. They only warn against the sawdust, and against burning the wood. Nothing against using it as a furniture, whatever the purpose. So I guess a picnic table should be good.

The other question is - does this treatment only protect against termites, or also against moisture? As in, would an open air picnic table be better with PT pine instead of regular pine?

[gjat]

Here in Florida, stick with the PT pine. If you stop at most FDOT rest stops and parks, the picknic tables are PT. It does help against the moisture as well. If you want it to last longer, wait until the dry season, let it all dry out, and treat with Thompson's water seal. It won't be dry until late fall at the rate we've been getting rain.

[siliconbauhaus]

Just make sure you use stainless fasteners in pt lumber.

[docrowan]

Moisture laden wood attracts termites and promotes the growth of fungus. (Termites won't eat, or even "see" very dry wood.) The ACQ is poisonous to both the termites and the fungus, therefore you will not see the rot problems in PT pine.

Siliconbauhaus raises a good point. The ACQ treated wood has 5 times the amount of copper compared to the old CCA treated wood. The copper will cause galvanic corrosion in regular steel and iron fasteners and the old galvanized fasteners did not have enough protection. Look for fasteners that are rated for ACQ, it will state it on the package.

[Rich P]

The PT will corrode galvanized metals...in fact Simpson came out with a "Z" line that is to be used with PT. Stainless is fine. Note that there are two "grades" of PT, one for ground contact and one for air. Ground contact costs more and you can't usually get it at the big box stores. Whenever I cut PT I always paint the ends with copper green...the 20% stuff. Even with the ground contact you will notice that the center of the lumber has not been totally penetrated.

[dielectric]

Huh, never realized that the "C" in ACQ is copper. That explains why the black phosphate screws I used in the sandbox bled all over within a couple of months. Everything I've built outside since then has been coated deck screws or full stainless. I wonder how long until the sandbox screws rust through and give out? I should probably go re-do it with the spare stainless screws just in case.

[cabinetman]

They only warn against the sawdust, and against burning the wood. Nothing against using it as a furniture, whatever the purpose. So I guess a picnic table should be good.

The other question is - does this treatment only protect against termites, or also against moisture? As in, would an open air picnic table be better with PT pine instead of regular pine?

I never did worry much about PT being toxic for furniture. The dust was a bit irritating. Wood that doesn't stay wet won't rot. I would rather use anything other than Thompson's. Regular applications of something as simple as a good outdoor oil (Penofin) would be better. Much of the PT may be SYP, which is a good choice for outdoor stuff.
.

[SARGE..g-47]

The toxic issue has been covered well here. I personally would not use the old style PT if kids were involved as I don't care for the arsenic content that was used. The new stuff I would consider but.. not the reason I posted.

Just a reminder to use a dust mask when doing the cutting... and you better plan on throughly cleaning blades and the guts of your machines you used to sever PT own. I had to replace a few steps the other day and it took me about 45 minutes to clean a TS blade.. my trunnions.. arbor.. etc. inside the cabinet. I hate to work with PT even though it has it's rightful place.

And also a reminder that when working wet PT be especially alert as it has a tendency to spread.. close... when severing that can cause havoc if you are not prepared. I have had PT pinch a splitter so bad it moved it and allowed the wood to touch the back of blade and you know what happens when that occurs.

So.. just thought I would add a few comments for any that might not be aware of the wonderful properties of PT when working with it.

[docrowan]

Sarge,

As always you make a good point. Most of the time when I use PT it is for carpentry projects and I cut it with my circular saw. Because of the copper content I try to blow out the saw thoroughly with compressed air to flush out the sawdust.

[gjat]

I never did worry much about PT being toxic for furniture. The dust was a bit irritating. Wood that doesn't stay wet won't rot. I would rather use anything other than Thompson's. Regular applications of something as simple as a good outdoor oil (Penofin) would be better. Much of the PT may be SYP, which is a good choice for outdoor stuff.
.

Why not on the Thompson's? I'm neanderthal, don't use anything on PT, but my Dad used to use it. Is it performance problems or application pain? I've never head of Penofin.