This is a guide to fiberglass repairs. These guidelines are for non-carbon graphite repair and for generic fiberglass repairs or repairs specific to SpecRacer Fords.
1. Hand Angle Grinder – A small hand grinder is recommended, a 4-1/2” grinder from your local hardware store works.
2. DA Sander – A DA (Dual Action) sander is recommended. An air drive sander works faster but an electric one will work. You can get either of these from your local hardware store.
3. Spray Gun – A low cost spray gun from Harbor Freight, the basic gun costs about $30. These guns are great for primer but not the best for finish coats. If you really want a great finish consider a better gun for the top coats.
1. Polyester Resin – Use only polyester resin for SpecRacer repaires. Epoxy resin is a lot more expensive and after you use epoxy resin you cannot use polyester resin, polyester resin does not bond to it. An example of a resin to use from Tap Plastics; http://www.tapplastics.com/product/fiberglass/polyester_resins/tap_bond_coat_laminating_polyester_resin/37
2. Fiberglass Mat – For most repairs, fiberglass mat works the best. It is held together with a bonding agent until the resin is applied. After the resin is applied, the mat bonding agent will release the fibers and it will conform to the body shape. We use the thicker or heavier mat to save time in layup. An example of a mat to use from Tap Plastics; http://www.tapplastics.com/product/fiberglass/fiberglass_fabrics/standard_glass_mat/89 Fiberglass Mat, 1.5 oz. (38” wide $2.75 per foot)
3. Primer – A polyester primer like Evercoat’s Feather Fill is a good product to use and is available from Summit racing for about $80 a gallon. The polyester primer is similar to the resin used in the fiberglass step and bonds well to the base resin.
4. Body Filler – A body filler like Evercoat’s “Lite Weight” filler is a good product to use and is available from Summit racing for about $25 a gallon.
5. Sandpaper – You will need sandpaper for the angle grinder, DA sander, and some for hand sanding. A rough and medium grit of 36 and 50 are good for the angle grinder. For the DA sander three grits can be used: 80, 180, and 320. For hand sanding grits of 36, 60, and 320 grit are required. The 320-grit paper should be wet paper to be used with flowing water remove dust. Wet paper also cuts faster than dry paper.
6. Top Coat – For a top coat we recommend using Summit Racing. The paint is of reasonable quality, good pricing and ships in a few days.
7. Other Supplies – You will need cheap brushes, gloves, tack rags, and mixing buckets. You can get these from your local hardware supply store or Tap Plastics.
Grind the cracks or repair spots using an angle disk grinder with a 36 grit wheel. Grind with the cut direction perpendicular to the direction of the crack. Grind to the full depth of the panel at the site of the crack. The width of the grind of the repair site at least 2 inches and more if is areas that have high stress like above the front wheel wells.
If the repair area is not self-supporting, additional steps will need to be taken. An aluminum plate can be pop riveted to add support or c-clamps and a backing plate can be used. If the support has the possibility of coming into contact with the fiberglass repair, a layer of household wax paper can be used as a barrier.
After preparing and supporting the repair, the area is ready for the application of fiberglass and resin. You will need a mixing cup, a means of measuring the catalyst, gloves, polyester resin, glass mat, and a paintbrush.
Getting setup prior to mixing the resin is important. First, cut or tare pieces of mat that match the repair areas. Different sizes of mat should be used, smaller ones will be necessary to fill the center or deeper part of the patch. Second, measure up the correct amount of resin and catalyst. Third, check to be sure everything is ready and forth, put on some gloves. Last, mix the catalyst with the resin and mix it thoroughly.
Now apply a coat of resin to the patch area. Place a piece of mat to the area and then proceed to add resin. Use the bush to work in the resin and to get out all of the bubbles. More of a poking rather than stroking action give better results. As the resin is worked into the mat, the mat will begin to release the binding agent and conform to the shape of the panel. After the first piece of mat is fully saturated and conforms to the panel, add another piece of matt. Add as many pieces of mat as necessary to fill the repair site to a level above the original height of the repair area.
Post Fiberglass Application Grinding
After the resin cures, about an hour or so, use a rough or medium grit disk grinder to remove excess fiberglass. Use the surrounding paint as a guide to the amount of grinding. Leave some excess fiberglass to be sanded later with the DA sander. If there are low spots that are not at the height of the finished panel, it is recommended that an additional layer of fiberglass be applied. If the low spots are shallow, a layer of body filler can be used but this will not add to the strength of the repair.
After the rough grinding, comes the pre-primer sanding. A dual action sander (air driven) or an orbital (electric) sander can be used. Start with rough sandpaper or a grit of 80 grit. Use this step to get the shape of the repair close to the correct anatomical shape of the body. After the shape is close to correct, go to a medium grit paper like 180 grit. This grit is used to remove the sanding marks created by the rough grit. The marks left with the medium grit paper will be filled in with primer.
First Primer Step
After sanding, the first primer layer applied. Clean the surface by blowing off with air to get all the dust off the panel. A polyester primer like Evercoat’s Feather Fill is a good product to use and is available from Summit racing for about $80 a gallon. The polyester primer is mixed up with the same proportions as the resin and uses the same catalyst. A cheap spray gun is recommended for applying this primer. Once the primer cures it is almost impossible to clean the gun, a cheap primer gun from Harbor Freight tools for about $40 is a good choice. Again measure out the primer and catalyst and a small amount of Acetone can be used to thin out the primer to spray better (about 5 to 10%). At this point, you should put on a respirator. When you are ready; mix the two, stir completely, and then transfer the mix to the gun. Apply the primer to the repaired areas of the body. Put on at least three very thick layers, it is OK if the primer runs or sags. It is important to clean the gun with Acetone right after you are done.
Post First Primer Filling
After the primer is dry, you will see areas of imperfections that will need to be filled with body filler or Bondo. The body filler can be used to fill low areas and/or voids left in the resin process. The body filler is also a polyester based product and is similar to the fiberglass resin and primer. Almost any reasonable quality body filler will work but a good place to get it is Summit racing. Use the instructions on the product to prepare the mixture. Use a plastic spreader to apply the body filler. Apply only as much as needed; remember you will have to sand off the excess. In addition, mixing multiple smaller amounts of filler that cure faster (using more catalyst) is usually better than large batches.
Post Body Filler Sanding
After the filler is dry, the primer and body filler is sanded. For this sanding step, a medium paper is used 180 grit. At this point, either a DA (dual action) sander, a vibrator sander, or a long board air sander can be used. The long board air sander works great for long flatter surfaces. Before sanding spray on very light coat of black rattle can spray paint. This fogged layer will be your guide coat to sanding. As soon as the black paint is sanded off, you will know you have sanded enough. Sometimes you will sand through the primer layer before sanding through the guide coat, this is typical and OK. These low spots will be filled with another coat of body filler or if they are very small or shallow, the next coat of primer might fill them.
Pre-Color Primer Step
After sanding the first primer layer, the second layer of primer is applied. Clean the entire section or panel to be painted. Use the same process to mix and spray the final coat of primer. Apply the primer to the repaired areas and the whole panel if necessary. Put on at least two thick layers and more in areas the still have imperfections. Remember to clean the gun with Acetone right after you are done.
Pre-Color Sanding Step
At the start of this step spray on very light coat or fog of black rattle can spray paint like the first primer step. For this sanding step, a finer paper is used typically 320 grit. Again, a DA (dual action) sander, a vibrator sander, or a long board air sander can be used. Another option is to use 320 grit-wet paper. Wet paper is used with water to remove the dust particles, wet sanding takes a little longer but usually give better results. After all or most of the guide coat is sanded off, you can move on to adding the color.
Color Spray Step
Before you spray the color layer, it is important that the surface be clean. The final surface can be cleaned with a wipe down of lacquer thinner of a good wash with soap. After the panel has dried, it is important to blow off and wipe down the panel with a tack rag. This will remove dust a particles that might remain. After the panel is dry and clean, you can start the paint process. The best place to paint is in a clean room but good results can be had outside or under cover of an overhang. If painting outdoors is best to not paint in direct sunlight or when it is windy. Now it is time to mix up the paint to the manufacturer’s specifications, put on a mask and start laying down the paint layer by layer. Put as many layers as necessary to get full coverage. If you plan to color, sand and buff the panel to get the best finish, consider adding an extra layer of paint. Be sure to clean the gun after use. If you do not plan to color sand and polish then all you are done.
Color Sanding and Buffing Step
If you are looking for the show or best looking paint at the track, you will want to color sand and polish the panel(s). The first step in this process is to wet sand the panel with 1500 grit paper. This paper removes, roughness, and imperfections in the paint. After sanding with this very fine paper, you will need to polish the panel. Use a slow speed rotary, not vibrating, polisher with rough polishing compound like 3M 5955 to get the best finish. It will require 2 to 3 applications of the rubbing compound to get the fine scratches from the 1500 grit paper removed. After the scratches from the 1500 are removed from the entire panel a final pass of a fine or glaze polish will get out the swirl marks out. At this point, you should have a high gloss finish ready for your favorite wax.