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Re: glu-lams and termite damage

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At 01:17 AM 5/22/98 -0400, you wrote:
>Can anyone provide guidance in repair of an existing glu-lam beam with
>In my particular case I have an existing glu-lam beam,  50 foot backspan with
>a 11 foot cantilever that has termite damage at the midspan of the backspan.
>The roof is a panelized system with 4x16 purlins at 8 foot on center by 24
>feet long. The glu-lam beam is 5-1/8 x 30 and the initial visable termite
>damage uncovered so far extends down at least 3 inches from the top of the
>glu-lam.  The original design was tight, so by subtracting out 4.5 inches of
>lumber for a net depth of 25.5 inches, the glu-lam no longer figures unless
>the live load gets down to about 10 psf (dead load is 12 psf).  The length of
>the visible damage along the surface is about 12 inches.  We plan on furthur
>investigating the extent of damage, but before proceeding too far, I would
>like to get the opinions or experiences of others.

I have been involved in several projects where we repaired over 200 GLB's
for dry rot and termite damage.  And I suggest the following:

 First I recommend that you carefully inspect this beam.  Not all termite
damage is visible from the exterior of the beam.  Termites, in my
experience in Northern California, attack wood that is wet.  The termites I
am familiar with apparently need some moisture to either survive and/or
digest the wood.  Many termites also need a connection to ground.  If these
termites travel to the soil they have tunnels along a path from their point
of infestation or wood damage to the ground.  If they have encountered
another wet area along this path then there is likely damage to this area.
I wouldn't be surprised if you found termite damage in other areas of the
building.   Also you would want to fix the leak that probably started this

Our testing for damage was done in this manner.  Visual testing included
removing damaged material to expose sound wood.   Coring with a small awl
like bit that brought out a 1/4" diameter core for visual inspection.  We
also tested the density of wood with sound measurement.  With a transducer
on one side of the beam a special hammer was rapped on the opposite side.
The time it took the sound to transverse the wood was measured.  As you
know the speed of sound through any object is a function of the density.  A
meter registered the time it took the sound to travel across the beam.  Dry
rot and termite damaged wood had reduced densities which showed up this
meter.  This method seemed to work very well.  Generally we also looked for
de laminations where lams were separated due to  wet and dry cycles.

Our repairs were done in many  ways all of which I think you proposed in
your e-mail.  An additional method of repair which we didn't use was epoxy
injection.  As your damage is in the top of the beam, presumably in the
compression zone, this might work for you.  As all of my work was in
schools and this method of repair was not acceptable to DSA  (The state
agency that plan checks and approves school and hospital construction)  I
don't know how effective it would be.  Having had the procedure explained
to me I think I would be very careful where I would use this solution.  

In California there are two testing labs that I know of.  One is in
Berkeley and is associated with the university.  The lab we used was Forest
Products Inspection, Ken Avila, at 707-995-9663.  I would not hesitate to
recommend Ken as I found him good at testing and full of knowledge about
GLB's.  He would know about epoxy injection.

In the course of our repairs  we treated the repaired areas along the
foundation with timbor.  This product, I believe, is basically boric acid
and though poisonous is relatively benign compared to some of the toxic
agents in use today.  Apparently boric acid in a powder or crystalline form
travels from the legs of the insect into the stomach when the termite licks
or cleans its legs.  The boric acid prevents digestion and the animal dies.
 We were careful with our application, and it was done by someone with a
license and knowledge of the material,  yet we had only moderate concern in
using it on school campus' where I don't think we would have liked to use
something more toxic.

I hope all this is some use to you.

David Carpenter