How To Repair Your Automobile Fiberglass

The most frequent problem we see with paint issues on fiberglass automobile bodies is the result of improper fiberglass repairs. That’s why we have decided to take the time to give you the basics on how to do this yourself—if you must. We could harp on how you should bring it to us because we are the professionals, but we have encountered way too many cases where someone along the way has chosen to take on the do-it-yourself fiberglass repair project…and honestly, we are just trying to do our part to cure the inevitable.

Note that we have included links to some of the products that we like to use for fiberglass repair here at the shop. Since this is a basic how-to on fiberglass repair, we suggest that you read the instructions for use and drying time included with all of the resins and primers mentioned below.

The first and most important step when performing a repair on fiberglass is to grind deeply into the panel ensuring that you expose the fiberglass mat below. Repair this with 3 to 4 layers of hand laid mat and Marson Resin, carefully working out all of the air bubbles with your brush with each layer. Sand with 3M 36 grit sandpaper to form and shape the repair. Finish ff with a resin based filler. Finally, sand that with 3M 320 grit sandpaper.

Next apply a catalyzed high build polyester primer (we prefer Slick Sand produced by Evercoat), to the repaired area and be sure to cover at least 12″ beyond the repair. Once dry, block the repair area using 3M 150 grit to start, moving to 3M 320 grit to feather the repair into the body lines. BE VERY CAREFUL to NOT break through the polyester primer during this step!  If you break through reapply the Slick Sand poly primer and block again.

Next apply 2k primer (also known as a urethane primer), we use PPG’s Global 2k Primer. Once dry, wet sand with 3M 500 grit. Another very critical step is to properly seal the repaired area. We suggest PPG Global Sealer in the color best suited to your top coat color. This sealer will stop shrinking between the different layers of products used in the repair. It also helps to avoid having the paint lift on the feathered edges of each layer in the repair.

And there you have it. Best advice for a project like this: Don’t skimp! Use quality products and take the time needed to get it right! Poor bodywork and paint are the most expensive mistakes made during a build.