) writes:
I am in the process of building a bankers dory. The Bill of Materials
calls for Marine Glue.

My partner wants to use an epoxy instead. Anyone been down this road
before?


When was the design published? Is it a reproduction using historical
materials?

Dories are traditionally held together with mechanical fasteners, ie nails
or screws. When wood gets wet is swells and closes the gaps so the boat
doesn't leak. On some boats, although I don't think on dories, the cracks
between the wood was stuffed with something that would also swell up when
it got wet and seal the cracks better. It's a bit tricky because if the
gaps are too small the wood fibres will get crushed when they swell and
lose their ability to close the gaps.

Up until the 1930's all sorts of things were used to try to stop leaks on
boats. They were usually called "calking" or "bedding" but not "glue".
Glue is supposed to be an adhesive, ie holds things togehter. Glues used
to be proteins, "glue" and "gluten" being from the same latin root. So
it's the protein in wheat flour that makes four-and-water paste stick, the
protein in milk which makes casein glue, the protein in skin and scales
that makes fish glue, and the protein in hooves and hide that makes
animal glue. None of the glues is very waterproof.

In the 1930's two new adhesvies were made from (petroleum?) chemicals,
urea formaldehyde and rescorcinol. Urea formaldehyde is generally called
"plastic resin" glue. It is water resistant but will break up if heated,
say in boiling water. It is called "cold waterproof", and sometimes
"weatherproof". Resorcinol adhesvie is waterproof. Both of these are thin
glues which have to be applied to pieces which fit closely with no gaps
more than 1/8 inch. They both dry hard and brittle. When sold as "marine
glue" the urea formaldehydde is a dry powder mixed with some wheator rye
flour to thicken it. Weldwood is (or was) a popular brand. I used a
different brand on one small plywood boat (Dogskiff) in combination with
wood screws. Where the parts didn't fit well I mixed in some sawdust for
extra thickener. It worked fine. There are some limitations like having to
be above 70 degress to cure. I was building indoors in winter and threw a
tarp over the boat and put a space heater underneath to "cook" the
plastic, a common practice. I've never used resorcinol but have read
accounts of others who have. The plywood motor torpedo boats and the
plywood aeroplanes (Mosquito light bombers) used in WWII were glued with
urea formaldehyde.

Epoxy (epoxides) is one of the post war chemical adhesives. ("Glue" should
probably be reserved for protein adhesives). Epoxy is waterproof and very
strong. The drawbacks are cost and toxicity. Cost is always an arguable
point and there have been many arguments about it. It becomes less of a
factor on large boats for which epoxy can be purchased in volume.



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