Use a sharp utility knife to carve out a V shape around the edges of the damaged area. Make sure to cut down through the color layer of the acrylic or fiberglass into the structure below. Usually, this means cutting down between 1/16 and 1/4 inch. If the surface is very hard or the damaged area is very large, a sanding drum or grinding disk attached to a drill or Dremel tool will make this preparation easier. Angle the sides of the damaged area so that the filler paste can be applied smoothly.
- Wipe the surfaces clean with cloths or paper towels, then use 220-grit sandpaper to slightly roughen the entire repair area. This slight roughening will help the paste adhere to the damage area.
- Clean the repair area with nail polish remover or acetate. At this point, make sure to ventilate the area well and use a ventilator mask. Wear protective gloves for the following steps.
- Transfer a small amount of paste filler from the kit into one of the provided mixing cups. If necessary, use the lightening or darkening toners to adjust the color to match your tub or shower (this is most often necessary with white tubs or showers).
- Add the catalyst agent to the paste in the ratio recommended by the manufacturer. Mix the ingredients together thoroughly to form the activated filler paste.
- Apply the activated paste mixture to the repair area using the mixing stick provided in the kit. Make sure to fully fill the damaged area. Overfill the patch area slightly; it will be sanded flush later.
- Allow the paste to fully harden for one hour, or according to the kit instructions. A heat gun can be used to speed up this drying time.
- Use wet/dry sandpaper to blend in the repair area with the surrounding surface. The best results are achieved if you sand in several stages using progressively finer grits of wet/dry sandpaper. Begin with 220-grit, then proceed by sanding with 320-, 400-, and finally 600-grit sandpaper. As you sand, drip water onto the sanding area with a wet rag to lubricate the surfaces.
- Clean away the sanding dust, then use the rubbing compound included in the kit to polish and blend the repair area with the surrounding material. High-speed buffing will give the best results—a buffing bonnet mounted to a drill or an automotive buffing tool is a good choice.
- If your kit includes a clear top-coat layer, apply it now, according to kit instructions.
Done patiently and according to instructions, the repair to your fiberglass or acrylic tub or shower should be nearly impossible to distinguish from the rest of the fixture.