How To Repair Auto Body With Fiberglass

Fiberglass is a fickle mistress. While amazing things can be created using a little bit of resin and fiberglass strands, information technology remains in a abiding land of hardening. Certain, one time the initial cure is completed, this procedure slows down significantly, over time the resin gets brittle. In the automotive surround, this ways cracks, breaks and splits in the body of your Corvette. Add to that some of the more than "adventurous" owners of many of these cars, you lot may have to repair fiberglass panels to get things back to normal. Accept for instance the 1967 Corvette convertible we have hither. In the 1970s, this was a cool show motorcar with a deep purple metal fleck paint job and an 8-71 blower hanging out of the hood.

The machine 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 Harm

Throughout this motorcar'due south life, there accept been some bumps and scrapes which accept caused some harm to the body. One of the worst was a separate under the rear deck on the rear firewall between the gas tank and the interior of the motorcar. A previous possessor had attempted a fiberglass repair, which we were able to remove with simply the twist of a screwdriver. This needed to be fixed the correct way. Nosotros also wanted to repair the original stinger hood that had been modded with a giant hole for the blower.

Yous tin can encounter a big vertical crack in the trunk. This needs to be repaired before moving on with the build of the car, or it will go worse.

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

Repairing A Fiberglass Fissure

In that location are several factors that become into making a skillful fiberglass repair. The fundamental is locking the new textile to the old. While cleanliness is paramount, that is only one-half of the equation. Fifty-fifty with the surface clean and prepped, a mechanical bond is needed to secure the actual repair. This is best washed by drilling a series 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">

Afterwards cleaning the area with an 80-grit sanding pad on a die-grinder, a series of holes were drilled into the trunk on either side of the crack. These are ½" holes. Information technology is also a good idea to drill the ends of the crack to stop its progress. The holes volition connect both sides of the repair, locking it all in place.

You don't need any special tools to mix fiberglass resin, just you exercise need to know how to mix it. Polyester resin is a two-part substrate that when properly mixed yields a work time of almost 15 minutes. The hardener, MEKP (Methyl Ethyl Ketone Peroxide), is added in very modest amounts compared to the resin base. Mixing small-scale 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 information technology puts off rut as it cures. When the ambient temp rises or falls from that point, hardener is either reduced or added to ensure a proper cure. Besides much hardener makes the resin brittle and it kicks besides fast, not enough and information technology might not kick at all. Resin historic period is important as well. Fiberglass resin (the base of operations) has a shelf life of well-nigh half dozen months. It can exist used across that, merely more hardener is required.

Mixing resin requires paying careful attention to the hardener ratio. If yous don't accept a syringe, y'all can count the drops. 12 ounces of resin takes around 25 drops, and so y'all will exist counting a lot and it is piece of cake to lose count.

But mix what you lot can use in about 15 minutes. When left in the mixing cup, the exothermic nature will speed up the curing procedure, rendering your mix into a solid block very quickly. On the motorcar, when it is spread out, this tin have an hour. A ratio of 2% hardener to resin is ideal, with i% being a tiresome cure for hot days and 3% being fast for cold days. Don't go outside of this ratio if you desire a quality repair. Measuring past weight, 100g of resin would demand 1ml of hardener. If yous are mixing large amounts of resin, a syringe is advisable for measuring the hardener. For reference, ane teaspoon equals 5ml.

The type of fiberglass mat y'all demand for your repair makes a divergence as well. There are several types of matting available, the most common being woven, chop mat, and loose fibers, all available in unlike weights. Chop mat, which has no blueprint, is just a series of one-2 inch long strands that accept 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 hands. This is good for large, flat areas where strength is needed. Woven mat is fantabulous for a top layer over chop mat for a uniform finish and heavy curves. Loose strands are best for building up a backing area, filling voids and for mixing your own reinforced body filler (think Duraglas®  or "kitty pilus"). For these repairs shown here, both woven and chop mat were used. The weights of the material take to do with the intended use. For automotive body repairs, the typical mid-weight mats available in any NAPA Automobile Parts Shop are perfect. If you are building your ain body panels, and then you volition desire to do more than research.

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

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 procedure was repeated on the underside of the trunk, completing the repair.

Repairing A Fiberglass Hole

Sometimes you need to ready 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. Notation 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 class the crest of the hood. We aptitude the metallic in a brake to become a crisp line downward the center. The underside of the metal was masked off as well. The panel was taped to the hood.

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

With the woven layer on, nosotros continues the procedure with chop mat, using a fiberglass docking roller to push out any trapped air bubbling. This adds a lot of strength to the repairs. We used almost 7 layers of mat for this repair.

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

Finishing

Finishing the repairs are just like any other fiberglass body work project. Sanding the repair polish and so using a body filler and high-build primer to finish it. Ane extra step should be taken, which is to use a sprayable polyester primer. This seals the fiberglass much like a gel glaze for a mill-perfect terminate.

The terminal step after the bodywork is the polyester primer. This stuff goes on thick and is and then sanded off polish. three-4 medium wet coats become the job done. This is over the filler work we did on the hood, but before the primary body work to the residue of the car. The polyester primer has to be block sanded.

Afterward paint, the hood is perfect, you would never know that in that location used to be a giant hole in the center.

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

Check out all the paint & trunk 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, chat with a knowledgeable expert at your local NAPA Automobile PARTS store.

Jefferson Bryant View All

A life-long gearhead, Jefferson Bryant spends more than time in the shop than anywhere else. His career began in the car sound industry every bit a shop manager, somewhen working his mode into a position at Rockford Fosgate as a production designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive announcer always since. His work has been featured in Auto Craft, Hot Rod, Rod & Custom, Truckin', Mopar Muscle, and many more. Jefferson has besides written iv 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.

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