CAC Pt Lumber test

OK we all "know" the new PT lumber "eats" fasteners. At least that is the warning. I decided to test it with a number of fasteners and materials including aluminum screen frame material, aluminum flashing and an assortment of common nails and screws. This is in CaC-C .15 saturation level "ground contact" rated PT that was the normal "wet to the touch" when I bought it.
I am tossing this assembly out behind my shed in the Florida weather for a while and let's see what happens. I figure in a year we will have a real result but I expect to see something going bad sooner if the fears are true.
http://gfretwell.com/ftp/PT%20lumber%20test%2010-25-13.jpg
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If this is the new "Copper Quaternary" pressure treated lumber, people might want to know "WHY" it eats fasteners.
They used to treat pressure treated lumber with a mixture of copper and arsenic salts dissolved in water.
The found that the arsenic was being leached out of pressure treated lumber in contact with the ground and showing up in shallow wells people used for their water supply. So, they banned arsenic in pressure treated lumber.
To get the same protection without arsenic, they had to quadruple the amount of copper in the pressure treatment liquid they force into the wood.
Since copper is more noble on the galvanic scale than either zinc or iron, when this new copper quaternary pressure treated wood gets wet, you end up with a lot more galvanic corrosion of zinc plated and unplated iron fasteners than you did with the old arsenic bearing pressure treated lumber.
So, now the recommendation is that people use triple galvanized or stainless steel fasteners and hardware on the new pressure treated lumber to allow for the much higher galvanic corrosion rates cuz of the increased amount of copper.
To make this experiment meaningful, you need to make sure that your pressure treated wood is in contact with the ground or a source of moisture all the time since the corrosion process is primarily galvanic corrosion. You won't get any galvanic corrosion in completely dry wood.
--
nestork


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On Tue, 29 Oct 2013 07:49:47 +0100, nestork

This is out in the weather in Florida. It will get plenty wet. It is certainly going to be a decent test of what will happen to a deck structure.
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...except for a deck that experiences a number of freeze-thaw cycles. I don't how that will impact the materials used, but you are certainly missing that in Florida.
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On Monday, October 28, 2013 11:49:47 PM UTC-7, nestork wrote:

Nestork, you de man! So refreshing to read a solid, scientific post -- by contrast with ...
HB
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snipped-for-privacy@aol.com writes:

Good idea. Sandy destroyed parts of my hand built PT fence. I used those painted deck screws for assembly. After 4 years, the deck screws showed no signs of corrosion.
--
Dan Espen

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wrote:

The assumption is stainless will be unaffected but I can shoot some SS in there.
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wrote:

The test is getting a change of venue. I am moving it down to the boat dock and I will screw it in with SS deck screws.
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snipped-for-privacy@aol.com;3141342 Wrote: > The test is getting a change of venue. I am moving it down to the boat > dock and I will screw it in with SS deck screws.
That would change the nature of the test. Virtually all pressure treated lumber is wetted by FRESH water in the form of ground water, rain or snow melt.
If you're in Florida, conducting your test at a boat dock is going to change the results because salt water is a much better electrolyte than fresh water.
One would expect considerably more galvanic corrosion with salt water than fresh water.
Maybe leave the piece of PT lumber behind your garage where it's typically only exposed to fresh water.
--
nestork


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On Wed, 30 Oct 2013 06:55:18 +0100, nestork

One of the issues seems to be aluminum and I am already testing that against .80 CCA lumber so it is a valuable test for me.
http://gfretwell.com/ftp/aluminum%20and%20PT.jpg
(about 15 years old) The water is not really that salty. Typically it ranges between 5 PPT and 25 PPT depending on the season. The ocean is in the 38-40 range. When the water is high enough to submerge the dock, the salinity is low.
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