Edit:
- line up the crack
- clean/degrease, sand crack for no sharp edges
- lay some glass on the back (we use 7725 twill but you can use chop mat from the aviation section of HD)
- I am not sure what vans uses for their resin but a polyester (basic stuff at HD) will work
- let dry
- move to the top/outside and run a layer of glass over crack
-sand
- paint
- fly