How To Repair Fiberglass Fenders

Fiberglass is a fickle mistress. While astonishing things tin be created using a footling fleck of resin and fiberglass strands, it remains in a constant land of hardening. Certain, one time the initial cure is completed, this process slows down significantly, over fourth dimension the resin gets brittle. In the automotive surround, this ways cracks, breaks and splits in the torso of your Corvette. Add to that some of the more "audacious" owners of many of these cars, you may have to repair fiberglass panels to get things back to normal. Take for instance the 1967 Corvette convertible we have here. In the 1970s, this was a cool evidence car with a deep regal metal fleck paint job 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 glass itself was in rough shape. Lots of cracks and breaks that needed repair. — The car had been sandblasted, which is a huge no-no for fiberglass, but moreover, the glass itself was in crude shape. Lots of cracks and breaks that needed repair.

Surveying The Impairment

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

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. — You can run across a large vertical crack in the body. This needs to be repaired earlier moving on with the build of the car, or it volition get worse.

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

Repairing A Fiberglass Crack

At that place are several factors that go into making a good fiberglass repair. The primal is locking the new material to the quondam. While cleanliness is paramount, that is only half of the equation. Even with the surface clean and prepped, a mechanical bail is needed to secure the bodily repair. This is best done by drilling a series of holes around the perimeter of the repair to lock it in.

After cleaning the area with an fourscore-grit sanding pad on a die-grinder, a serial of holes were drilled into the trunk on either side of the crack. These are ½" holes. Information technology is as well a skilful idea to drill the ends of the crack to finish its progress. The holes will connect both sides of the repair, locking it all in place.

Yous don't need any special tools to mix fiberglass resin, simply you practise demand to know how to mix it. Polyester resin is a 2-role substrate that when properly mixed yields a work time of about xv minutes. The hardener, MEKP (Methyl Ethyl Ketone Peroxide), is added in very small amounts compared to the resin base. Mixing small batches typically ways counting drops from a canteen. In that location is a proper ratio based on room temperature of 76 degrees. The mixture is exothermic, which means information technology puts off heat as it cures. When the ambient 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 plenty and it might non boot at all. Resin age is of import as well. Fiberglass resin (the base of operations) has a shelf life of about 6 months. It can be used across that, but more than hardener is required.

Mixing resin requires paying careful attention to the hardener ratio. If you don't have 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 easy to lose count. — Mixing resin requires paying careful attending to the hardener ratio. If you don't take a syringe, you lot can count the drops. 12 ounces of resin takes around 25 drops, so you will be counting a lot and information technology is easy to lose count.

Only mix what you can use in about 15 minutes. When left in the mixing cup, the exothermic nature will speed upwards the curing procedure, rendering your mix into a solid block very speedily. On the car, when it is spread out, this can take an hour. A ratio of 2% hardener to resin is platonic, with 1% being a slow cure for hot days and 3% existence fast for cold days. Don't get exterior of this ratio if you want a quality repair. Measuring by weight, 100g 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 yous need for your repair makes a departure every bit well. In that location are several types of matting available, the almost common being woven, chop mat, and loose fibers, all available in different weights. Chop mat, which has no design, is just a series of one-2 inch long strands that have been pressed together into sheets. This is the strongest blazon of mat, only information technology does not lay downwardly very smooth and it can come up apart hands. This is proficient for big, flat areas where strength is needed. Woven mat is excellent for a acme layer over chop mat for a compatible terminate and heavy curves. Loose strands are best for edifice upwards a backing area, filling voids and for mixing your own reinforced body filler (remember Duraglas® or "kitty hair"). For these repairs shown here, both woven and chop mat were used. The weights of the textile have to do with the intended utilise. For automotive body repairs, the typical mid-weight mats available in any NAPA Machine Parts Shop are perfect. If y'all are building your own body panels, then you will desire to do more research.

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

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

The brush was used to push the resin into the mat. The mat will become transparent when it is fully wet. This was layered three times. — The brush was used to push button the resin into the mat. The mat will become transparent when it is fully moisture. This was layered three times.

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

Repairing A Fiberglass Hole

Sometimes you need to fix a mod that was done by a previous owner. This stinger hood was modified so a blower could stick out, but that is not the direction of this build. Rather than buy a new hood, we opted to fix it. Note the holes have been drilled around the perimeter. — Sometimes you need to fix a mod that was done by a previous possessor. This stinger hood was modified and then a blower could stick out, but that is non the direction of this build. Rather than buy a new hood, we opted to prepare it. Annotation the holes have been drilled around the perimeter.

The top side of the repair was taped off, and a piece of sheet metal was used to form the crest of the hood. We bent the metal in a brake to get a crisp line down the center. The underside of the metal was masked off as well. The panel was taped to the hood. — The top side of the repair was taped off, and a piece of sheet metal was used to form the crest of the hood. We aptitude the metal in a brake to become a crisp line downwardly the center. The underside of the metallic was masked off as well. The panel was taped to the hood.

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

With the woven layer on, we continues the process with chop mat, using a fiberglass docking roller to push out any trapped air bubbles. This adds a lot of strength to the repairs. We used about seven layers of mat for this repair. — With the woven layer on, we continues the process with chop mat, using a fiberglass docking roller to push out any trapped air bubbles. This adds a lot of strength to the repairs. We used almost 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 place and ready for finish work. — The end results of the repair matched the crest of the original hood, and the repair is fully locked in place and gear up for terminate work.

Finishing

Finishing the repairs are just like whatever other fiberglass body piece of work project. Sanding the repair polish and so using a body filler and high-build primer to finish information technology. One extra stride should be taken, which is to utilize a sprayable polyester primer. This seals the fiberglass much like a gel coat for a factory-perfect terminate.

The last step after the bodywork is the polyester primer. This stuff goes on thick and is then sanded off smooth. 3-4 medium wet coats get the job done. This is over the filler work we did on the hood, but before the main body work to the rest of the car. The polyester primer has to be block sanded. — The last footstep after the bodywork is the polyester primer. This stuff goes on thick and is then sanded off smooth. 3-4 medium moisture coats get the chore washed. This is over the filler work we did on the hood, but before the chief trunk 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 giant hole in the center. — After paint, the hood is perfect, you would never know that at that place used to exist a giant hole in the centre.

The procedure shown here tin be used for whatever type of fiberglass construction, including boats, RVs and campers, even shelters. The key to a good fiberglass repair is 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 one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to repair fiberglass, conversation with a knowledgeable skilful at your local NAPA Auto PARTS store.

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 manufacture every bit a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever 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.