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Burning fence posts?

Warren David

Joined: Nov 18, 2010
Posts: 186
What is the green stuff a lot of fencing is treated with and is it ok to use this treated wood for firewood?
Al Loria

Joined: Apr 21, 2010
Posts: 395
Location: New York
If it is pressure treated wood, don't burn it.  The older stuff has arsenic and copper in it, as I remember.  The sawdust from cutting it was even dangerous, so burning it cannot be any better.  The newer treated wood is supposedly less toxic, but I would not even burn that.

Brenda Groth

Joined: Feb 01, 2009
Posts: 4433
Location: North Central Michigan
no, do not burn them, you breathe the smoke, you breathe in put the ashes on your  garden, you  feed your plants arsenic

a better use would be to use them..they can be put in paths as steppers, or on terraces to hold back soil, if they are still solid they can be used to build raised beds and other fencing or trellising, esp in areas where food will not be produced, but generally if they aren't new they won't be leaching out any of the product from them after they have aged a bit.

I have used old treated posts in the property as edgings and other things..with no problems


Bloom where you are planted.
Warren David

Joined: Nov 18, 2010
Posts: 186
Thanks for all the replies. I shall take your advice and wont be burning it. It's just a couple of posts from a fence I took down at a customers house last week. I threw the rest of the fence away because it had so much wire and screening attached to it.
Tim Canton

Joined: Sep 14, 2010
Posts: 174
Al Loria wrote:
If it is pressure treated wood, don't burn it.  The older stuff has arsenic and copper in it, as I remember.  The sawdust from cutting it was even dangerous, so burning it cannot be any better.  The newer treated wood is supposedly less toxic, but I would not even burn that.

the new stuff is still pretty toxic just no the still sell the ACQ  lumber for agricultural purposes so fence posts are likely to still be the old stuff.    The new stuff is all residential materials
John Polk

Joined: Feb 20, 2011
Posts: 6879
Location: Currently in Seattle. Probably moving 1 hour north by end of the year.
I'm not certain what they put in the new 'safer' green stuff, but the old stuff was called "Cuprinol" (sp?).  It was copper based...not safe to burn.  If it is "treated" wood, it is treated with something to kill anything that can harm wood.  Since it is still green, I'm guessing that there is still oxidized copper in it.  Do not burn it, do not chip it for mulch, do not...Hell, I'm not certain I even want to handle the stuff without rubber gloves.
Ken Peavey

Joined: Dec 21, 2009
Posts: 2523
Location: FL
The chemicals used in treating pressure treated wood has changed over the years as information became available.  Way back in the day, creosote was used-not the same stuff that builds up in your chimney.  Problems in manufacturing led to the development of CCA-Chromated Copper Arsenide.  CCA was cheap, easy to use, and effective against water and insects.  The residual Arsenic meant that chronic exposure was a health hazard, the guys working at the sawmills often had the shakes.  It had to go.  The replacement was ACQ.  ACQ is a form of copper quaternary.  Its effectiveness in protecting wood is questionable.  I've worked with the stuff.  Boards cup and warp, entire truckloads have been sent back by retail outlets because the boards have arrived infested with termites.  The stuff is junk, but at least your baby wont be poisoned if you feed it 20 picnic tables.  It's only practical advantage is that it sheds water.  The ACQ lumber is of such poor quality that I know of contractors who wont use it unless absolutely required by building codes.  Untreated oak lumber, although more expensive, is far more durable than ACQ and I've seen it used in place of treated lumber.

Burning any of this stuff will alter the chemicals and release them into the atmosphere.  If used in a residential woodstove, these vapors will be released into and around your home.  The old style creosote boards are probably mostly gone by now, having been phased out back in the 70s.  CCA is still around in massive volume and still will be for decades to come-that stuff holds up.  CCA, while being great for construction durability, is about the worst stuff you can have in your fireplace or compost heap, in wood or ash form.  High temperatures are required to destroy the chemicals, and woodstoves dont always reach the temperatures required.  Even if they did, the residual materials are just as destructive.  The primary effect of high level, chronic exposure upon microbes is death, and the stuff holds up for decades.  The debate continues as to the leaching of the chemicals into soil.

If you only have a few boards to burn, I doubt the trace amounts will have much impact.  If you have a lot of boards, you might consider building a shed or fence rather than burning it.

I purchased a truckload of lumber last weekend to build a greenhouse.  Out of all that lumber, 3 boards are pressure treated-a 4x6 beam and 4 2x6 planks which will all be used where the greenhouse contacts the ground.  The rest of the stuff will be stained.

Seed the Mind, Harvest Ideas.
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