spider Cracks?

[wdnboatbuilder]

Could it be caused by the fact that polyester's never stop hardening.

[Buckle]

wdnboatbuilder - I think you may be mis-guided somewhat. There are many wife tells in the industry, I think you many have half the story using the expression "polyester's never stop hardening".

When you catalyst a polyester or vinly ester product, be it gel coat, barrier coat, resin etc, the product will reach a state of cure after a given time frame. Lets assume after 24 hours at room temperature, the laminate will cure to have a HDT (heat distortion temperature) of 28. If you were to measure the HDT after a month at room temperature, this would have risen to something typically around 50/55 degrees C.

HDT can be influcenced by many factors, such as cataylst/accelerator quantities, type of resin system, mould technology, laminate design, manufacturing schedule etc, etc.

You would of most probably heard of post curing. Post curing is basically about increasing the HDT of the laminate and gaining the advantages that follow such as stabilization of the laminate (very important for surface finish issues etc), better mechanical properties etc, etc. The aim of post curing is to subject the laminate to a temperature greater than that it would be subjected to operate in. Generally, the hotter the post cure, the higher the HDT.

But what happens if you dont post cure the product? - Well the product typically undergoes its own natural post cure, althought most people aren't aware of it. The environment in which you boat etc is in is constantly undergoing a post cure cycle by means of the sun. Look at the side of any boat. The side which usually faces south has weathered to a great degree than the opposite side.

Going to back to the laminate after a month's worth of room temperature cure, the HDT would rise from 55 to 70 odd when subjected to natural heat.

If the laminate undergoes heating to a degree greater than the Tg (glass transition temperature) of the laminate, the laminate will naturally creep, leading to stress concentrations, which typically lead to gel coat cracking etc.

I think you may of basically being trying to say what I have just said. If you didnt, you learn something each day.

Remember, go forth and increase you HDT today.

Buckle

[wdnboatbuilder]

Fair enough