sealing fiberglass

[alvingra]

once you have fiberglassed the stringers in your boat do they require any kind of seal to be applied to fiberglass.

[Dutch Peter]

Originally Posted by alvingra

once you have fiberglassed the stringers in your boat do they require any kind of seal to be applied to fiberglass.

No, the fibreglass is sealing enough if it encapsulates the stringers completely.

[Ilan Voyager]

It's not exactly answering to your question but if you have to fiberglass wood stringers or plywood with polyester resin it helps a lot to seal first the wood or plywood with a polyurethane varnish. When the varnish is very tacky you make your fiberglass. I've learnt this tip by a technical paper of the german company Vosschemie in the beginning of seventies.

The theory behind this technique is that polyester does not bond to wood for two reasons;
1/ polyester is a poor glue.
2/ wood contains phenols that inhibate the polyester cure.

The polyurethane which is a very good glue makes an interface between wood and polyester resin.

It works pretty well for parts which are never permanently in water.

Besides, it's good to seal the polyester with a gel coat which absorbs less water and protect eventually fron the UV.