[Rokeby]

Neil,

I'm not convinced that your plans to use a wood glue/fiberglass laminate is a good idea. This from my history as a professional boat builder with experiences in composite construction from 65 ft fishing vessels to small skiffs, canoes and kayaks. It is widely held that boat builders are a conservative bunch. Well, I've been one of them, and perhaps as a result I'm over cautious. So be it. Here are my thoughts.

Fiberglass composite construction has been around since the early 1950s. In the time since there have been many (r)evolutions in the types of fabric used; woven and non woven; symmetrical and non symmetrical; different materials; glass, aramid, carbon fiber, etc. But through it all the choice of resins has been severely limited, and for the most part survived the test of time. Almost without exception, and at least as far as availability to amateur builders, the preferred resins are epoxy and polyester. The combined system of glass cloth - of whatever physical characteristics - and epoxy/polyester resin is highly refined with a high degree of repeatable success.

I take it that the primary reason for your choice of wood glue is cost. I feel that given wood glue's unproven record, its use is a false economy. As between epoxy and polyester resins, polyester is by far the less expensive. I have never encouraged amateur builders to use polyester resins due to its greater health risks. However, in your case I would urge you to consider it, being mindful of personal safety concerns which might include full coverage (Tyvec suit, gloves) and airmask with air supplied from outside the working space.

My specific concerns about the unproven use of wood glue are many. They include:
* possible brittleness of the dried wood glue
* adherence of the glue to the 'glass cloth used
* achieving a near 1-1 cloth/glue mix (1-1 by weight is the ideal epoxy-polyester'cloth ratio for max strength, lowest cost. Dunno if it's the same for wood glue.
* full drying of the glue. The desired thickness of wood glue in a joint is down around one-thousandth of an inch, much of the water in the glue is taken up by the wood, the rest is dissipated by evaporation. Also, ideal clamping pressure is around 100 psi. In your case, the relatively thick glue layers - there will be no clamping pressure - can dry by evaporation only. A possible comparison is vinyl, water based, paint which has a much greater film thickness than alkyd, oil based , paints. Water based paints take a full 30 days to completely dry.
* resistance to cyclical loading. This is critical for the laminate in way of the attachment of the suspension bits, critical areas. This can only be verified by actual testing. It's not completely relevant here, but aircraft parts/joints are vibration tested under load to millions of cycles.
* final stiffness of the structure. I'm not confident that layup schedules that would provide adequate stiffness with epoxy/polyester will do so with wood glue. This can only be verified with side by side testing.

I wish you the greatest success with your project. To achieve the success you are working so hard to achieve, I recommend you take the time to fully reconsider your choice here, including what testing is in order. It wouldn't surprise me that a comprehensive testing program will take 3 or 4 months to research, devise and implement.

Rokeby