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Re: pressure-treating glu-lams

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Mike,

How a glu-laminated beam is to be treated depends on the manufacturer,
specifications if they already exist regarding required retention
percentage, material type, use, architectural issues, etc.

Treating prior to lamination is a very effective way of ensuring a good and
long lasting protection.  Typically Southern Yellow Pine is treated in this
way in the Southeast United States.  Probably the most expensive
alternative!

Douglas fir is typically treated by incising the members, the little "cuts"
in the beam, to ensure a deep penetrating treatment.  But, architects don't
like to see the incising marks on beams.  You'll typically see D.F. on
outdoor play structures, girders for wood bridges because they're hidden
underneath, etc.

Both of these examples are the difference between open and closed cell wood.
Without getting too deep it's a material property issue and how the material
absorbs the chemicals.

Remember, the odors of treated beams are usually pretty strong.  Make sure
there is plenty of outdoor ventilation.  For example, don't treat a whole
rafter that sticks out of a building by only a couple of feet.  In that case
you would apply a coat of treatment by hand if necessary.

Hope this quick explanation helps.

Best Regards,

Brian McMahon, E.I.T.
Universal Timber Structures, Inc.
brian(--nospam--at)utsdesign.com





----- Original Message -----
From: "Michael Livingston" <mlivingston(--nospam--at)yolles.com>
To: "SEAINT (E-mail)" <seaint(--nospam--at)seaint.org>
Sent: Tuesday, November 27, 2001 3:32 PM
Subject: pressure-treating glu-lams


A fellow engineer in my office asked me about pressure-treating glulams
for exterior exposure.  I don't know the specifics of her project, but
she was told that each lamination needed to be individually
pressure-treated prior to fabrication instead of just the exterior of
the finished beam getting the treatment.  Is this true?  Is it due to a
limitation of the pressure-treating equipment or are the joints
susceptible to decay?
Thanks,
Mike Livingston

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