Bonding fiberglass to polyurethane

How do I bond anything to polyurethane? In particular, I want to bond fiberglass or carbon fiber to it.

I have been using polytek 74 series polyurethane. This is good stuff. It gives my mold the surface that I want. However, it is very expensive. So, instead of just building a box and pouring a gallon of this stuff in it to mold my object. I would like to brush it on, or otherwise put a thin coating of it on my object. Then to get the rigidity in my mold. I will lay up fiberglass over the polytek.

The problem is, I have been told that cured polytek will not bond with much of anything. I know it won't bond to itself. Even uncured polytek won't stick to much of anything.

What can I apply to the polyurethane after I have brushed it on and let it cure, that will allow me to bond fiberglass to it?


Thank you.

Karl

Hi Karl,

Although unfamiliar with your urethane material, if it has a fairly soft surface hardness, then you might try micro-perforating the surface you wish to bond to.
I believe that Aerospace Composites in the USA would help here with some sort of roller having small pins protruding from the surface.

If the surface is hard, then you could do what we used to do. To adhere GRP to waxy plastics and angle-grind the surface lightly all over before applying a gel coat resin.

I hope this helps you.

What about trying...Polyurethane? The Wood glue kind? I use it to bond epoxy carbon fibre to brass with a little moisture to aid curing.

If that does not work or the area is too big, maybe plaster of paris as a support? This combination is often used in mold making for ceramics.

It may work unbonded too, as a separate layer.

Hi Karl - Your PU supplier will have a primer for the PU allowing other adhesives such as epoxy to bond to it. But read up on making epoxy/fibreglass moulds. Easy and straightforward. Make plug / apply gelcoat / apply fibreglass laminate. Very similar to what you plan just leave out the PU. Peter