I wouldn’t do that if I were you. I have been around this forum for couple of years now and I have never read a recommendation from any of the experts to do it this way. The guy in the link you provided – in my opinion – missed the main point in the reply he got from uncle something. The main ingredient wasn’t the flour, it was the polyester resin which is combatable with the resin you will be using on the fiberglass. The flour, Cabosil or wood dust are only fillers to add thickness to the resin. Few things came to my mind when I read his recipe
- It is dough made from organic materials (i.e. vegetable oil) pretty much like pizza, so will it rot under the glass?
- If so, would it cause the wood it is touching to rot as well?
- Is it compatible with polyester resin? In other words, will it have any impact on the curing characteristics of polyester resin?
I don’t have the answers for these questions nor the time to experiment, so – personally – I would not take this risk.
I am speculating that the size of the boat that guy was building made him comfortable improvising such an unorthodox way to save few bucks. There is not much to risk to begin with. If you want a simpler alternative to Peanut Butter, you can fill this gap with PL Construction Adhesives. Give it 48 hours to cure, sand and glass.
I will be very interested to hear from the guys here what they think about this.