CCA treated wood has its good points and its bad points, on several
levels. Specific to your first question "do the agents of pressure
treated wood provide resistance to fungal attack, or is it merely for
preventing infestation?"

CCA is a good poison in that it kills pretty effectively both decay fungi
and wood boring insects. The CCA solution is forced into the wood by a
pressure chamber process. The wood is placed on carts and rolled into the
pressure vessel. The vessel is closed tight and a vacuum is applied to
remove some of the air and moisture from the wood. The vessel is then
flooded with the CCA liquid treatment and pressurized to drive the CCA
treatment liquid into the wood. The wood is treated under pressure with
the CCA liquid for a given amount of time and then the vessel is
de-pressurized, drained and a vacuum (negative pressure) is used to get
some of the excess CCA liquid off of the wood.

There are several factors that determine the effectiveness of the
treatment.
- Type of wood
- Size of wood
- If the wood is seasoned or un-seasoned
- Concentration of CCA in treatment liquid
- Pressures used during process
- Length of process

One of the problems that is not uncommon is for the interior of the
treated wood to not receive the desired CCA material. If you cut into a
piece of CCA treated wood you can frequently find the interior core as
bright wood without staining from the CCA treatment. The larger the cross
section of wood the greater the volume of possible untreated wood.
Looking at the end grain of an un-cut piece of CCA treated wood will not
be informative as to the depth of penetration. In many applications this
protective shell can be beneficial however once the protective shell is
broken with a crack, check or saw cut, much of the long term protection
is compromised.

Railroad ties and utility poles are pressure treated with one of several
processes. What has been happening in resent years is that the pressure
treated wood is being also protected with Borate based wood
preservatives. This additional application is able to penetrate into the
volume of wood that were missed by the pressure treatment and provide a
back-up protection for when the shell is compromised or the interior
moisture is severally elevated.

So when you buy pressure treated wood how much of the wood is really
pressure treated?

Question two, "what is the process of rot with these agents, bacteria or
fungus?"
Make the assumption that the attack of decay is by a fungus. Bacterial
decay of wood is much less common.

Now how about some answers as to health and safety issues, both personal
and environmental, based on the use of CCA and other such pressure
treatments of wood.

Your truly,

Mr. Borate

========
Robert Cagnetta wrote:

> I found, once again, some rotted pressure treated wood about 20 years
> old.  I'm curious, do the agents of pressure treated wood provide
> resistance to fungal attatck, or is it mearly for preventing
> infestation?  And also, what is the process of rot with these agents,
> bacteria or fungus?
>
> Curious in RI