I was once asked what I thought of PVA wood glue.
the common brand in Australia is called Selleys Aquadhere.
a chap I know was trying it in the wood parts of his aeroplane.
now while it is a really good glue for furniture work it is not ever to be used in aircraft.
remember that hot summer day I mentioned in the previous post?
what I asked him to do was get his heat gun and warm up one of his joints to see what happened.
next time I saw him (later that afternoon) all the colour had drained from his face.
all the glues that we use in aircraft are thermo setting plastics when cured.
there are two types of plastics, thermo setting and thermo softening.
if you heat a thermo setting plastic it just sits there getting hotter.
If you heat a thermo softening plastic it gets softer and softer until it melts.
Aquadhere, or PVA glue, is a thermo softening plastic and as it is heated it softens. as it softens the glue strength rapidly diminishes.
What my friend found when he heated the joint is that it fell apart.
On a hot summers day his aeroplane could have, would have, had a structural failure in flight.
We only learn new things by experimentation but you have to understand what you are doing.