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Re: Wood Adhesives

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Charles Greenlaw wrote:
> 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.

**Sounds like a hull of a way to build a boat, I mean a shearwall!  But it might be 
  possible to get some nails into this connection (to guard against "letting go    
  explosively) by using a "palm nailer", as must frequently be used in seismic 
  retrofitting work.  James Bela

> 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.