Determine whether your Jacuzzi is made of acrylic or gelcoat fiberglass. Acrylic Jacuzzis are formed by heating the material, molding it into the shape desired and then coating the surface with fiberglass. Gelcoat fiberglass is made of polyester resin that is molded, colored and then reinforced with glass particles. Call your Jacuzzi manufacturer or search the company's website. Or use P320-grit sandpaper to gently rub the crack in your fiberglass Jacuzzi and then smell the sandpaper. Acrylic is odorless, but gelcoat is not.
Choose a tub and shower repair kit that matches your Jacuzzi surface and color.
Use a putty knife to gently hollow out the crack in your Jacuzzi until you create a groove of 1/16 to 3/16 of an inch deep. Wipe the area clean with a paper towel and then wrap the putty knife with P-320 grit sandpaper to smooth inside the groove. Sand the surrounding surface also to lightly smooth away the transition from the Jacuzzi repair area.
Clean the Jacuzzi repair area with nail polish remover to eliminate grease or oil residue from soaps or body creams, as well as the wax residue from the sandpaper.
Tape off the repair area with painters tape to protect the surrounding Jacuzzi surface. The fiberglass repair gel will bond to any exposed area.
Put your dust mask on and ventilate the work area if possible. Mix the fiberglass filler with the hardener as instructed on your Jacuzzi repair kit. Use a mixing bowl and a hard wooden stick for a thorough mix.
Fill the Jacuzzi repair area with fiberglass filler using the putty knife. Press down with the knife to pack the fiberglass filler into the groove. Wipe the putty knife with a paper towel, and then smooth the Jacuzzi repair area to eliminate any hump.
Use a hair dryer to speed up the drying of the fiberglass filler. Wait one hour, and then press the Jacuzzi repair area lightly with your finger to make sure the surface feels hard. Use a soft cloth and the rubbing compound that comes with your Jacuzzi repair kit to gently buff the repair area until it is smoothed away into the surrounding surface.