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.
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
To get the same protection without arsenic, they had to quadruple the
amount of copper in the pressure treatment liquid they force into the
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.
> 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
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.
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.
(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
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