How to make polyester waterproof

Agreed Ondarvr, insufficient wetout would be a concern, regardless of resin system employed. I wasn't picking on you, just trying to be clearer.

 

Yane, by now you know that the problem is caused by faults in the laminate, which you can repair by grinding and filling with polyester. There probably were some particles of wood in the glass mat when you applied the resin.

I assume getting a can of epoxy will not be easy in Macedonia, nor is it here.
But the guy who sold you the resin and glass mat also has bags of talcum powder (probably from Korcula). Mix resin and talcum until you have something with the viscosity of yoghurt, add a bit of catalyst and paint the whole surface with it. The talcum powder delays the curing process a bit but that's good because temperatures are high already.
That gives you a thick, waterproof layer- I call it a Balkan gelcoat - that you can sand and paint if you wish, but you can also leave it like it is.

 

I already grind and fill the air bobbles (they occur only on the pin wood, like rails on the bottom and bumpers on the sides, not on the plywood, actually plywood is almost perfect laminated. Probably I made mistake not laminated ply first and then put reals and side bumpers). This air filled blisters occur during the process of drying, thy were not present during the phase of wetting. How the drying take place they appear. I was not able to flatten those area no mater how much resin I put.
This Balkan gelcoat idea I like Very much
I was considering to first put spry putty and then to put more resin over it, your idea is better.
But instead of talcum powder from Korcula I'll use baby powder from Italy, it smells like Adriatic so I'll enjoy the smell of Adriatic sea in my waterproof poly on ply fishing boat fishing on the Macedonian Lakes


Thank you for this helpful advice