Yes, applying a gel coat over the patched area after using Bondo fiberglass repair is recommended to enhance waterproofing and provide a smooth finish. The gel coat helps seal the repair, protecting it from water exposure and UV damage. Additionally, it can improve the overall appearance of the hot tub, ensuring a more uniform look. Make sure the Bondo is fully cured before applying the gel coat for best results.
Depending on the amount of rust you can bondo the holes. You will ned to cut the rusted parts. If the area is large then fiberglass will make a better and more durable repair than bondo.
Bondo doesn't require cloth, but it's not very strong. It's intended to fill small shallow imperfections. Cloth is usually used with fiberglass resin, which is used to repair fiberglass bodies structurally.
Bondo is the industry standard.
Go to the automotive section of your local Wal-Mart and get some Bondo (fiberglass resin) for small repairs, or Bondo Glass (fiberglass threads and resin). You can adhere pieces like completing a puzzle with the plain resin or fill in large holes with the threads and resin. I also suggest fiberglass mat if you need to completely recreate a piece.
What I do is, rivet sheet metal behind crack. Fiberglass patch and resin. Then Bondo.
It is generally not recommended to put fiberglass over aluminum, however, people do it. An epoxy polymer resin is usually suggested, and the fiberglass should be very clean.
Bondo.
It is possible for a person to put a color into fiberglass. This is common with people who own fiberglass boats.
bondo would probably work well its used for replacing chunks of fiberglass that have fallen of of cars so it is very sticky.
I think they have patch kits, but you have to drain below the area so it is dry. You mix the resin, slob it on a cloth and put a few layers over the hole. i think one for a car sold in auto body sections (along with the bondo in a can) would even work since fibreglass is fibreglass. After it drys , run a sander over it and viola.
from my experiences with bondo would be inproper adhersion to the metal being that there may have not been enough hardener added or not mixed properly. over time the product(bondo) could become brittle and crack.