We have a pond fountain that is based on a 4 foot tall fibreglass pot (brass tube up through centre, etc). The original finish degraded so I sanded it back and painted on Zinsser sealer then a pool-rated top coat. About 6 months later the top coat started to show small lumps of various sizes as the paint started to come free all over. Have stripped this back, and realized that as the pot is fibreglass, maybe Zinsser not the right sealer / base product. Need a fibreglass sealer (I guess) but not sure what is best. Would paint it on, then aim to paint over it with the pool paint again. Don't need fibreglass sheeting for repair - just the surface sealed as I hope this will act as a good base for the paint.