During engine bay restoration, I came across a crack on the driver side fender skirt. It was located on the thin strip of fiberglass where the radiator support bracket attaches to the fender. Fortunately it was small, and the repair was very easy.
The crack is obvious in this picture, and hopefully the other details help identify its location.
With a 1/16" spherical engraving dremel bit, I removed the damaged fiberglass. A bright light is useful for following the crack through the SMC. You can see by the prep work, there was more to the crack than it initially appeared.
With the damaged SMC removed, I placed aluminum tape on the backside. I did this repair in conjunction with the fender well seam separation repair so I could use one batch of Kittyhair. Wearing nitrile gloves, I pushed Kittyhair into the crack and let it cure.
When I removed the tape, I smoothed the back side down with a small, conical grinding stone and dremel. The side shown was smoothed by block sanding.
SUMMARY: This was a 2 out of 10. The trickiest part is ensuring all the damaged fiberglass has been removed and the crack ground out, otherwise it may grow again. Once that's done, the rest is straight forward.
Engine Bay Crack Repair