How to repair a damaged sandwich part:

http://vimeo.com/moogaloop.swf?clip_id=18019742&server=vimeo.com&show_title=0&show_byline=0&show_portrait=0&color=ff9933&fullscreen=1&autoplay=1&loop=0

This video shows an approved way to repair damaged sandwich structures, e.g. aircraft wings and fuselages. Unfortunately only the repair of the outer layer is shown, but this might still be interesting for some people. If both surfaces of the sandwich are damaged the repair becomes more complicated, unfortunately I haven't found a video yet which shows how it is properly done. I'll try to post some pictures if I find them again...

Properly done this repair is as strong as the original part.

The English translation in this video is horrible, but pictures tell more than words anyway. Take note of the proper scarfing of the composite top layer, how the honeycomb is glued in with resin and resin filled with microballoons (the brown goo). What is not being mentioned explicitly but very important is using the exact same number of fabric layers as the original part, and laying it up in the exact same orientation. If in doubt the piece that is removed from the part can be burned to remove the resin and the fibers then inspected for fabric weight and orientation.

The very important part of this repair is how the patches are applied on top of the sandwich: start with the LARGEST piece of fabric, and then apply the smaller ones. The other way round will NOT result in a structurally sound repair! This might sound illogical, but that's the way it is done!

What's unfortunately missing is the final sanding and painting.