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Subject: Pest management

Pest management

From: Marc A. Williams <artcons>
Date: Saturday, August 4, 2001
Tamara Lavrencic <tamaral [at] gh__hht__nsw__gov__au> writes

>Can anyone direct me to people or organisations who have used heat
>treatment to eliminate borer in historic buildings? I have been
>investigating the potential use of this treatment method on a very
>fragile wooden cottage, but need to demonstrate that it's been used
>on a similar building, preferably somewhere with a similar climate
>to New South Wales in Australia, ie, temperate.

Heat can be used as a successful treatment for insects.  However,
there are several caveats that must be discussed first.  By heating
hygroscopic materials, the air surrounding them will be at very low
RH (probably below 5%) and the moisture content can fall
significantly.  The duration of heating and the degree to which they
are protected by a moisture barrier or moisture buffering are also
factors.  For unrestrained single materials, this may not be a
problem.  However, restrained constructions and composite objects
(for example paint on wood) may be damaged.  High temperatures also
accelerate chemical reactions, including oxidation and degradation
reactions.  However, for a building this is probably not a
significant issue, since naturally occurring temperatures within
attics often are near the temperatures necessary for insect control.

In order to be sure of insect kill (eggs, larvae, adults), a
temperature of 130 degrees F must be maintained for 12 hours.  In
practice, this is much more difficult than it seems.  It is unclear
if the building under consideration is intact or disassembled.  I am
assuming it is intact, which is a more complex treatment process.
This temperature and duration must be held at the interior of the
wood in the coldest location.  Generally, this will be at the lowest
level of the building (heat rises) in the interior where the
material mass is thickest.  Depending upon the heating method, it
would not surprise me if a week or more of heating was required to
achieve this temperature.  The rise from ambient to about 120
degrees F will be relatively fast, but the rise to 130 degrees will
be progressively slower and will take the majority of the time.  It
is important to actually measure the temperature in various
locations that are suspected to be the coldest.  It is not always
possible to predict where this will occur.  It goes without saying
that the thermometers must have remote sensors, as humans can not
live long at 130 degrees either.

I have used heat as a pest control method for entire rooms within
historic buildings in a temperate environment (New Hampshire, USA).
However, I have not done an entire building, so you will have to
extrapolate from my experience.  In order to hold a temperature of
130 degrees at the coldest location, it was necessary to set the
control at 140 degrees, and some areas of the room reached this
temperature.  We utilized box fans within the room to very
aggressively move the air.  High air circulation is necessary to
eliminate cold spots and raise the temperature as quickly as

The room air was at 140 degrees within 1 hour, but the interior of
specific storage boxes (the coldest location) required 36 hours to
reach 130 degrees, plus an additional 12 hours held at 130 degrees
to kill the insects.  The treatments were done to control insect
infestation in collections within the rooms, not in the
architecture, but there was the intent to "disinfect" the
architectural surfaces as well.  The walls were plaster on lath with
painted doors and trim.  Objects consisted of textiles, mattresses,
some furniture, and a few decorative objects.  Many objects and
boxes were placed in polyethylene bags to minimize moisture
movement.  No damage was noticed to either the building or the

Marc Williams, President
American Conservation Consortium, Ltd.
85 North Road
Fremont, NH 03044 USA

                  Conservation DistList Instance 15:15
                 Distributed: Wednesday, August 8, 2001
                       Message Id: cdl-15-15-007
Received on Saturday, 4 August, 2001

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