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Re: Wood Adhesives

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At 10:25 AM 7/22/99 -0700, Bob Bossi wrote:
>10 or so years ago, when I was chair of the SEAOC Code Committee I was
>approached by 3M who had developed a (marine?) adhesive and was seeking an
>ICBO Evaluation Report for plywood glued to studs shear walls.  I don't have
>copies of the data they gave me but their (monatomic) test results were very
>impressive.  You might try contacting them..   Make sure the block is kiln
>dried and attached to the rafters as well
>

And Nels Roselund has offered:

>When you develop an assembly with the structural characteristics you need, 
>you'll need to write a detailed sequence and procedure for the workers, train 
>them (because it will be something they haven't done before), and establish 
>quality controls to assure confidence that the work is properly performed.  
>No visual verification is possible after the job is completed.  Without a 
>commitment on the part of the workers to do a good job, work in those 
>hard-to-reach places when no one is watching may not get properly done, and 
>you'll never know for sure.
>

My comments: I have solved this same problem several times. I have a
contractor friend and client who is an avid wood boatbuilder. He recommended
3M No. 5200 for this application, based on personal experience and its
reputation among boatbuilders. It is a one-part, humidity-curing urethane
dispensed from caulking gun tubes, and unlike boatbuilding epoxy glues, does
not have a heat-related pot life problem, or a dispensing nuisance.

The stuff is sold by boatyard supply houses and isn't cheap.

I arranged for my friend to be special inspector on the first job, and I did
it myself on another, smaller one, where we glued a 2x4 plate to the plywood
diaphragm underside, and built a conventional shear wall up under that. A
neat solution for a small remodel. This was in a very fussy and diligent
jurisdiction, and was satisfactory to them, perhaps in part because of my
contractor friend and myself being well known there.

As noted by Kelly Cobeen in a recent SEAOC Convention Proceedings paper,
glued joints hold until they let go explosively, without "ductility", so the
safe elastic value of the glued connection needs to be in excess of the most
the structure can ever inflict on it under ultimate strength conditions. 

I would be inclined to glue in 2x4 blocks flatwise to the sheathing as
intended, and then use 1-1/4 inch non-shrinking OSB-like rimboard (as
supplied for I-joist systems) cut into blocks, and face nailed to both top
plate edges and to the edge of glued 2x4 flat blocking, and liberally
toenailed  to rafter faces. The upper 2x4 flat blocks might even be
pre-nailed from the vert rimboard blocks, and the L-shaped result glued up
to the diaphragm simultaneously with being nailed to the wall plate and
rafters. Rotation of the between-rafter vert blocks that would put the glue
in tension needs to be prevented.

An upper limit of the glued value in psi might be the APA-given "rolling
shear" limit of plywood between plies. See the APA Plywood Design Spec for
that. For OSB something analogous probably exists. Field-installed glue
shear in psi may well not be the upper bound on the glued connection, but if
not, probably the ultimate strength of the nailed shear wall is lower yet.

Charles O. Greenlaw SE    Sacramento CA
-----------------------------------------------
>"Robert Fennema, P.E." wrote:
>
>> I am designing a detail to correct a construction defect. The
>> contractor failed to install blocking and boundary nailing at the top of
>> the shear walls perpendicular to the roof rafters. This is only one of
>> the many shear transfer connections omitted from this 12,000 SF home.
>>
>> Of course the roof covering is on. It is a two piece clay tile system
>> set in mortar.  We would like to repair the defect without removing the
>> roof covering to install the missing boundary nailing.
>>
>> Am considering gluing a 2 x 4 block flat onto the underside of the OSB
>> roof sheathing and connecting it to a new block on the shear wall using
>> an A35. I need help selecting the adhesive that would substitute for
>> the lack of boundary nailing.  Does anyone know the shear transfer
>> values of various adhesives that might be available?  I guess this would
>> be expressed in # per sq in.