Nautix PO is a high performance protective primer, recommended for osmosis prevention, and formulated with a Desmodur™ resin which hardens by reacting with air moisture. 
This paint offers strong adhesion and protection over GRP substrates, and can prevent osmosis over GRP if you apply 5 layers minimum. It can be overcoated with antifouling for underwater areas and with undercoat/finishing paint above the waterline. 
This primer is very easy to use, allows application in delicate outside weather conditions (can be applied from 0°C), dries quickly and should not be sanded between layers.