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Date: | Wed, 21 Apr 1999 16:50:56 PDT |
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John Warsaw wrote
> Has anyone tried making bottom boards from pressure treated plywood with
> pressure treated lumber around the edges? Any opinions? I've read
> different views on the use of pressure treated lumber, and would paint it
> with oil-base primer and topcoat to help seal in the chemicals. (I'm in
> the USA, where pressure treated lumber is CCA.)
Work done in the 1970's in the USA showed that timber (lumber) treated with
CCA (copper chrome arsenate) could give a residue in hive products. This was
for timber used in boxes and not painted. Even though the CCA formulation is
supposed to have the arsenic bonded in an insoluble form by the chromium,
trials have shown that there is still a certain amount of leaching of the
arsenic. This would be the case inside a beehive, particularly if there is
condensation.
The opinion of our woood chemists here in Australia at the time was that by
painting the exposed surfaces of the timber, you would stop any leaching of
the arsenic. It should not bleed through the paint if the timber is dry.
So you would need to ensure that the timber is dry. If possible, the timber
should be treated rough, dried and then dressed to remove any CCA salts that
may be on the surfaces. This is then painted.
Trevor Weatherhead
AUSTRALIA
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