A fine crack had appeared in the top of the seat tube on my 10 year old Giant Defy Advanced road bike. A highly stressed area and a real problem if it fails while riding. The repair consisted of grinding the paint and filler back, inspecting the outside of the tube - nothing obvious - perhaps a hair of resin starvation in the original carbon tube. Inspecting the inside of the tube - nothing. Then I applied multiple layers of epoxy compatible glass fibers "clamped" in place with tape. After curing and filing smooth - the area was masked into a "pointed" shape. Then a layer of thickened epoxy applied, dressed smooth and then painted black to match the bike trim. No attempt was made to blend the repair down to original thickness. It was left proud with extra reinforcing material to be sure the area was stronger. The blending away in a pointed shape to distribute stress. The black paint masks the repair by making it visually obvious!
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