After the CATO of the reinforced rocket (Tachyon IV) at Doonside, I have rebuilt a new reinforced bottle and pressure tested the entire rocket last night to 170psi. There were no visible stress marks on it so should be good to go for this Saturday.
I am also replacing the fin section on this rocket with 3mm plywood fins directly glued to the bottle. I coated the fins with 5 minute epoxy to add a little strength and water proofing. They will be sanded and painted tonight.
At the last Doonside launch event a couple of the members suggested trying vinyl paint for the rockets. I bought some white vinyl and plastic spray paint at SuperCheap Autos, but at $15 a can that is not all that cheap. I tried the paint on a PET bottle a couple of days ago. I lightly sanded half of the bottle with very fine sand paper and left the other part untouched. After a few goes I realised that you have to spray in multiple thin coats to get good coverage without runs. The paint dried within minutes.
The paint is a little flexible so bending and squeezing the bottle had no effect on it flaking off, like we have had with other paints. The paint on the unsanded side, however, did come off very easily when scratched with a finger nail. It was a different matter on the sanded side though. The paint held very well even when scratched. I'm keen to see how well it holds up in the sun with heat and UV.