How To Repair Fiberglass Fender

Fiberglass is a fickle mistress. While amazing things can be created using a niggling bit of resin and fiberglass strands, it remains in a constant state of hardening. Certain, once the initial cure is completed, this process slows downwards significantly, over time the resin gets brittle. In the automotive environment, this means cracks, breaks and splits in the body of your Corvette. Add to that some of the more "adventurous" owners of many of these cars, you may accept to repair fiberglass panels to get things back to normal. Take for case the 1967 Corvette convertible we have here. In the 1970s, this was a cool show machine with a deep imperial metallic flake paint task and an 8-71 blower hanging out of the hood.

The car had been sandblasted, which is a huge no-no for fiberglass, but moreover, the drinking glass itself was in rough shape. Lots of cracks and breaks that needed repair.

Surveying The Damage

Throughout this car's life, there have been some bumps and scrapes which have caused some damage to the trunk. I of the worst was a split nether the rear deck on the rear firewall between the gas tank and the interior of the auto. A previous possessor had attempted a fiberglass repair, which nosotros were able to remove with just the twist of a screwdriver. This needed to exist stock-still the right style. Nosotros too wanted to repair the original stinger hood that had been modded with a giant hole for the blower.

You can run into a large vertical crack in the torso. This needs to be repaired before moving on with the build of the car, or it volition become worse.

The previous owner had attempted a repair on the underside, but this simply popped off with a screwdriver, not expert. Fiberglass is not an adhesive; it merely doesn't work that way.

Repairing A Fiberglass Crack

There are several factors that go into making a good fiberglass repair. The central is locking the new cloth to the old. While cleanliness is paramount, that is but one-half of the equation. Even with the surface make clean and prepped, a mechanical bond is needed to secure the actual repair. This is best done by drilling a serial of holes around the perimeter of the repair to lock information technology in.

" data-medium-file="https://knowhow.napaonline.com/wp-content/uploads/2017/04/Vette_glass_03a.jpg" data-large-file="https://knowhow.napaonline.com/wp-content/uploads/2017/04/Vette_glass_03a.jpg" loading="lazy" class="wp-image-17114 size-full" src="https://knowhow.napaonline.com/wp-content/uploads/2017/04/Vette_glass_03a.jpg" alt="After cleaning the area with an 80-grit sanding pad on a die-grinder, a series of holes were drilled into the body on either side of the crack. These are ½" holes. It is also a good idea to drill the ends of the crack to stop its progress. The holes will connect both sides of the repair, locking it all in place." width="800" height="534" data-lazy-src="https://knowhow.napaonline.com/wp-content/uploads/2017/04/Vette_glass_03a.jpg?is-pending-load=1" srcset="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7">

After cleaning the area with an 80-dust sanding pad on a dice-grinder, a serial of holes were drilled into the trunk on either side of the crack. These are ½" holes. Information technology is also a good thought to drill the ends of the crack to cease its progress. The holes will connect both sides of the repair, locking it all in place.

Y'all don't demand any special tools to mix fiberglass resin, merely y'all do need to know how to mix it. Polyester resin is a 2-role substrate that when properly mixed yields a piece of work fourth dimension of almost 15 minutes. The hardener, MEKP (Methyl Ethyl Ketone Peroxide), is added in very small amounts compared to the resin base. Mixing small batches typically means counting drops from a bottle. In that location is a proper ratio based on room temperature of 76 degrees. The mixture is exothermic, which ways it puts off oestrus equally it cures. When the ambience temp rises or falls from that betoken, hardener is either reduced or added to ensure a proper cure. Likewise much hardener makes the resin brittle and it kicks too fast, not enough and it might not kicking at all. Resin age is important besides. Fiberglass resin (the base of operations) has a shelf life of about 6 months. It can exist used beyond that, only more hardener is required.

Mixing resin requires paying conscientious attention to the hardener ratio. If you don't take a syringe, you can count the drops. 12 ounces of resin takes around 25 drops, so you will be counting a lot and it is like shooting fish in a barrel to lose count.

Only mix what you can use in about fifteen minutes. When left in the mixing cup, the exothermic nature volition speed up the curing process, rendering your mix into a solid cake very quickly. On the motorcar, when it is spread out, this tin can have an hr. A ratio of two% hardener to resin is platonic, with 1% existence a slow cure for hot days and 3% being fast for cold days. Don't go outside of this ratio if yous want a quality repair. Measuring by weight, 100g of resin would need 1ml of hardener. If y'all are mixing large amounts of resin, a syringe is advisable for measuring the hardener. For reference, 1 teaspoon equals 5ml.

The blazon of fiberglass mat you need for your repair makes a deviation as well. In that location are several types of matting available, the most common being woven, chop mat, and loose fibers, all bachelor in different weights. Chop mat, which has no blueprint, is just a series of one-2 inch long strands that have been pressed together into sheets. This is the strongest blazon of mat, simply it does not lay down very smooth and it can come up apart easily. This is good for large, flat areas where strength is needed. Woven mat is fantabulous for a top layer over chop mat for a compatible finish and heavy curves. Loose strands are best for building up a bankroll area, filling voids and for mixing your ain reinforced body filler (think Duraglas®  or "kitty hair"). For these repairs shown here, both woven and chop mat were used. The weights of the material have to do with the intended utilise. For automotive body repairs, the typical mid-weight mats available in any NAPA Automobile Parts Store are perfect. If y'all are edifice your own trunk panels, then y'all will want to do more enquiry.

First, the body was treated to a base coat of resin. This serves to hold the mat in place.

Side by side, we added a layer of chop mat.

The castor was used to push the resin into the mat. The mat will get transparent when it is fully wet. This was layered three times.

The process was repeated on the underside of the torso, completing the repair.

Repairing A Fiberglass Pigsty

Sometimes you lot need to gear up a modern that was done by a previous owner. This stinger hood was modified so a blower could stick out, but that is non the direction of this build. Rather than buy a new hood, we opted to set up information technology. Note the holes accept been drilled around the perimeter.

The top side of the repair was taped off, and a piece of sail metallic was used to form the crest of the hood. Nosotros bent the metal in a brake to get a well-baked line downwards the center. The underside of the metal was masked off as well. The console was taped to the hood.

We started with a layer of woven fiberglass to exist the top layer.

With the woven layer on, we continues the process with chop mat, using a fiberglass docking roller to push button out whatsoever trapped air bubbles. This adds a lot of strength to the repairs. Nosotros used most 7 layers of mat for this repair.

The end results of the repair matched the crest of the original hood, and the repair is fully locked in identify and ready for end work.

Finishing

Finishing the repairs are just like any other fiberglass body work projection. Sanding the repair smooth so using a body filler and loftier-build primer to finish it. I 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 last footstep afterward the bodywork is the polyester primer. This stuff goes on thick and is then sanded off smooth. 3-four medium moisture coats get the job done. This is over the filler work we did on the hood, simply earlier the main torso piece of work to the rest of the car. The polyester primer has to exist block sanded.

After paint, the hood is perfect, you would never know that there used to be a behemothic pigsty in the centre.

The process shown here can be used for any blazon of fiberglass structure, including boats, RVs and campers, even shelters. The key to a good fiberglass repair is make clean preparation, patience, and practiced quality components such as 3M resins and matting.

Check out all the paint & body productsavailable on NAPA Online or trust ane of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more than information on how to repair fiberglass, conversation with a knowledgeable practiced at your local NAPA AUTO PARTS shop.

Jefferson Bryant View All

A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry every bit a shop managing director, somewhen working his way into a position at Rockford Fosgate equally a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist always since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin', Mopar Muscle, and many more. Jefferson has likewise written 4 books and produced countless videos. Jefferson operates Scarlet Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.

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