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