Automotive patch repair fiberglass

The key is locking the new material to the old. While cleanliness is paramount, that is only half of the equation. Even with the surface clean and prepped, a mechanical bond is needed to secure the actual repair. This is best done by drilling a series of holes around the perimeter of the repair to lock it in.

Polyester resin is a 2-part substrate that when properly mixed yields a work time of about 15 minutes. Mixing small batches typically means counting drops from a bottle. There is a proper ratio based on room temperature of 76 degrees. The mixture is exothermic, which means it puts off heat as it cures.

When the ambient temp rises or falls from that point, hardener is either reduced or added to ensure a proper cure. Too much hardener makes the resin brittle and it kicks too fast, not enough and it might not kick at all.

Resin age is important as well. Fiberglass resin the base has a shelf life of about 6 months. It can be used beyond that, but more hardener is required. Only mix what you can use in about 15 minutes. When left in the mixing cup, the exothermic nature will speed up the curing process, rendering your mix into a solid block very quickly.

On the car, when it is spread out, this can take an hour. Measuring by weight, g of resin would need 1ml of hardener. If you are mixing large amounts of resin, a syringe is advisable for measuring the hardener. For reference, 1 teaspoon equals 5ml. The type of fiberglass mat you need for your repair makes a difference as well. There are several types of matting available, the most common being woven, chop mat, and loose fibers, all available in different weights. Chop mat , which has no pattern, is just a series of inch long strands that have been pressed together into sheets.

This is the strongest type of mat, but it does not lay down very smooth and it can come apart easily. This is good for large, flat areas where strength is needed.

Woven mat is excellent for a top layer over chop mat for a uniform finish and heavy curves. For these repairs shown here, both woven and chop mat were used. The weights of the material have to do with the intended use. If you are building your own body panels, then you will want to do more research. Finishing the repairs are just like any other fiberglass body work project.

Sanding the repair smooth and then using a body filler and high-build primer to finish it. One extra step should be taken, which is to use a sprayable polyester primer.

This seals the fiberglass much like a gel coat for a factory-perfect finish. The process shown here can be used for any type of fiberglass structure, including boats, RVs and campers, even shelters. The key to a good fiberglass repair is clean preparation, patience, and good quality components such as 3M resins and matting.

Know How. A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer.

In , he began writing tech articles for magazines, and has been working as an automotive journalist ever since. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.

Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Skip to content Fiberglass is a fickle mistress.

The car had been sandblasted, which is a huge no-no for fiberglass, but moreover, the glass itself was in rough shape. Lots of cracks and breaks that needed repair. You can see a large vertical crack in the body. This needs to be repaired before moving on with the build of the car, or it will get worse.

For any cracks or fractures, grind directly on the crack, removing any rough or damaged material. Scuff the entire surface that will get fiberglass applied to it. Clean the surface of the affected area using a rag and acetone to remove any dirt or grease. This is crucial for a solid bond. Tear the fiberglass mat to size so it covers the damaged area.

Tear the number of layers needed to bring the damaged area level with the surrounding surface. Tearing instead of cutting fiberglass mat eliminates visible edge lines on repair patches. Add catalyst to a small bucket of resin following the recommendations on the container.

Thoroughly stir the catalyst into the resin using a stir stick. Wet the surface of the repair with the resin using a 4-inch felt roller. Apply the first layer of mat and saturate it with resin using the felt roller. When the entire layer is full of resin, roll out any air bubbles using an air roller. Repeat this process for each layer of mat until the repair is complete. Let the fiberglass harden. Sand the fiberglass repair using grit sandpaper on a sanding block until it's smooth and level with the surrounding surface.