On Wed, 31 Dec 2008 00:11:01 -0700, wrote:

Thanks for this info. As well, I wanted to see if an ammonia solution
could be used instead of bicarbonate, so I did some googling, and found
a discussion of the chemistry involved. Turns out that various bases or
basic salts can be used resulting in, I suppose, various chemical
properties of the casein glue since it specifically mentions that casein
glue formed using lime has a known assoiation with aviation related wood
gluing. Here is the link
http://www.dotapea.com/english/chap03casein.htm

There's another article on casein linked from that page, but needs
translating from French.

A.L.

casein if protected from fungal attack is still an acceptable glue for
some aircraft work. typically gliders in dry climates that are not
left out in the rain.

the chemistry of the glue is one thing but what really matters is the
long term stability of the chemistry in the overall joint.

resorcinal formaldehyde, invented in the early 1930's, is the oldest
glue for aircraft use. the need for near perfect joint gaps, 70psi
jointing pressure and about 70degrees F jointing temperature make it
more difficult to use than the new boy on the blocks Epoxy Resin.
(dont sue me on the numbers, they're from memory)

some glues have disgraced themselves along the way by failing in
service.
acid catalysed phenolics like Selleys 308 are not usable for aircraft
because too much formic acid in the joint gradually destroys the wood
layer abutting the joint leading to in service failures.
PVA glues become thermoplastic at high temperature and will fail
underload.

just be carefull with aircraft glues. what you want is a glue that
forms a chemically stable compound after achieveing the joint
strength. it is never just a matter of sticking stuff together.
Stealth Pilot