Many guitar bodies are made with a deep polyester clear coat to give it a shiny, glossy appearance. Although polyester provides a tough protective coating, it can be chipped and gouged with enough force. The good news is that this damage can often be invisibly repaired using liquid polyester resin. The process is fairly time-consuming, but patience will pay off. Take your time and work carefully, and your guitar body will end up looking as good as new.
Thoroughly clean the blemish to remove any dust or oil.
Sand the blemish with 400-grit sandpaper to create a good bonding surface.
Apply a coat of polyurethane filler and allow it to dry for at least two hours. Sand with 400-grit sandpaper, and clean any dust with a damp cloth. Apply another coat of filler, then allow it to dry. Sand again and wipe clean.
Apply successive layers of sealer, allowing each coat to dry for at least one hour. Sand each layer smooth if bubbles or imperfections form.
Once the blemish is completely filled, sand the patch perfectly smooth with 400-grit sandpaper.
Spray successive layers of polyester-compatible lacquer, sanding lightly between layers, using the paint sprayer, until the surface texture matches the surrounding finish.
Hand buff to a high gloss using a clean cloth.
If the underlying wood of the guitar body was also damaged, you may need to retint the wood with a matching stain or paint before repairing the polyester finish. If the base coat of polyester is tinted, you'll need to add a matching tint to your polyester sealer before applying it. Several manufacturers produce polyester repair kits that include all the materials you need for instrument finish repairs.
Polyester resin products can emit harmful vapours, especially when used in a sprayer. Always use adequate ventilation or a respirator when using these products. Improper use of polyester resin products can further damage your guitar's finish. Always read and follow the manufacturer's instructions when using these products. Double-check with the manufacturer's specifications to make sure the products you are using are compatible with your guitar's finish.