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Re: pressure-treating glu-lams

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Mark,

	Thanks for pointing this out, Mark.

	This brings up an interesting question; how do you detect hidden rot in
large pressure treated members?

	I don't have a project requiring this information; I'm just asking out
of general curiosity.

	Thanks in advance to anyone who replies.

				Best regards,

				H. Daryl Richardson

Mark Gilligan wrote:
> 
> The problem with pressure treating large pieces of wood is that the
> pressure treatment only extends about an inch into the wood even when
> incising is used.  Thus much of the interior of the section is untreated.
> 
> When wood checks it can allow water to get to this untreated wood which in
> turn results in the center of the piece rotting.  The surface does not rot
> because it is treated but the interior will be worthless.  This is a real
> problem with large pieces of lumber.
> 
> Thus for pressure treatment to be fully effective in glu-laminated lumber
> you want to treat the laminations prior to gluing.   When this is done it
> is necessary to plane the laminations after the treatment process.  The
> problem is that the shavings from the planing process are considered
> hazardous waste because they have been treated, and as a result most
> laminators are not willing to go to the bother, so you may have to settle
> for treating  the laminated member.
> 
> Mark Gilligan
> 
> ++++++++++++++++++++++++++++++++++++++++++
> 
> From: "Brian M. McMahon" <brian(--nospam--at)ubsdesign.com>
> To: <seaint(--nospam--at)seaint.org>
> Subject: Re: pressure-treating glu-lams
> 
> 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
> 
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