My IH SMC truck hood project involved repairing a large hole. This was one of my largest hurdles to the whole project. This is what I initially saw.
The picture is showing the hood upside-down on a work table. The hole is the result of some sort of long-ago impact the shattered the composite material and did significant damage. My first reaction was to just repair it from the backside. This hope was lost when I quickly discovered that there was not any access to the backside of the repair. At least not without cutting some support structures out of the way. Which would mean that I would need to rebuild those after I repaired the hole. Not impossible, but it seemed like a lot of work.
I began this repair like any other, with the surface preparation. The hole got larger as I removed all of the damaged material and created a transition area.
The edge of the hole was a razor”s edge as I transitioned out to the existing finished surface. I also used some sandpaper to sand around the inside of the hole to allow epoxy to adhere to the inside surface when I put in my patch.
My strategy was to create a thin layer of composite using epoxy resin and 3oz Chopped Strand Mat. The layup was done on a piece of plastic and allowed to cure. Once cured, I cut it to be about 1/2 inch larger than the hole. Then I mixed up some thickened epoxy and applied it around the perimeter of my patch and placed it in the hole. I had already placed a sheet metal screw in my patch, and attached a wire to a support to hold the patch in place until cure.
In the picture you can see the patch, the wire, and the support. The tension on the wire held the patch in place until the patch was cured in place. Next I worked to add material from the front to fill in the low spot. This returned strength to the laminate and restored the surface profile back to where it should be. I again used 3oz Chopped Strand Mat and started with small diameters and worked out to larger ones until the surface at the correct level.
Now most of the surface has been filled in, and it can be ground to remove any high spots, air bubbles, and allow
for adhesion of the next layer.
Now I can fill the low spots with thickened epoxy or bondo and sand the surface to match the surrounding areas and get a nice finish.
This is how a repair should be made. A nice transition in the existing laminate will keep the repair from cracking or breaking in the future. After the bodywork is complete nobody will know it was repaired.