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Re: Epoxy for Wood Repair

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On 27 Sep 2007 at 11:00, Tom.Hunt(--nospam--at)fluor.com wrote:

> 
> 
> Antonio, 
> 
> I have never used it but I hear carpenters swear by Gorilla Glue. 
> 
> Thomas Hunt, S.E. 
> Fluor 
> 
> 
> 
> 
> ASLCSE(--nospam--at)aol.com 
> 09/27/2007 10:42 AM 
> Please respond to seaint 
> To
> seaint(--nospam--at)seaint.org 
> cc
> 
> 
> Subject
> Epoxy for Wood Repair 
> 
> 
> Hello again, engineering friends. 
> 
> What is the best suited EPOXY to use in Wood Repair (cracked DFL beam)
> in "combination" with bolts holding it together. 
> 
> Thanks 
> 
> Antonio S. "Tony" Luisoni 
> Consulting S.E. 
> Granada Hills, CA 
> 

I just wanted to caution against the use of Polyurethane Glue, like
Gorilla Glue.  There is an interesting article in Fine Woodworking
magazine, Aug 2007 No. 192, that has tested various glues in a
bridle joint, which is an open mortise and tenon joint.  The tests
were done on three types of woods and the joints were milled to
three levels of joint tightness when dry-fit, tight, snug, and loose.

The best glue in the test was Type I PVA glue (waterproof), like
Titebond III.  The worst in the test was polyurethane glue with
only 58% of the strength of the Type I PVA glue. Slow set epoxy
like System Three T-88 was the second best in the test.

Polyurethane glues swell and foam to fill joints but they don't have
strength through that glue matrix when cured, like the epoxies do.

To the OP: Are you going to be drawing the crack closed with the
bolts?  Are there going to be stresses on the cracked joint after
the adhesive cures?  If you are going to be drawing the crack
closed, I would use PVA glue and "clamp" the joint tight with
the bolts and allow it to cure.

Take Care,
Lloyd

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