Fiberglass Bathtub refinishing keeps peeling

[JoeThomas]

My fiberglass bathtub is peeling again, and needs to be refinished again for the third time. It generally happens when temperature wavers between hot and cold I noticed (70 degrees to 40 degrees Farenheit weather within a day). When I step on the bathtub during the cold night, thats when it cracks. Its happened twice before. We are doing fiber glass refinishing. Are there any options to ensure it doesn't happen again? We do sanding before refinishing. The bathroom has no crawl space vent, its in an older building. Also, when a shampoo bottle or soap drops on the bathtub, it will create light cracks which may start peeling.

Note: Everytime its refinished/painted, I do not use the shower for 2 days, 48 hours.

 

[Tuttles Revenge]

I've never refinished an entire fiberglass tub, but we've had repairs done by people who specialize in fiberglass repairs. All but one repair you could never tell that the tub had been broken.

I would imagine tho, that if its just a painted on re-surfacing, the material isn't bonding or there is too much flex to the tub and it looses adhesion. Is there any way to add some structure under the tub to prevent flexing? I've done it by pouring in self leveling mix from the wall to get under shower bases, but I had to create a dam at the drain box.