Maintenance: Fix cracks on wing tips.

Following about 170 hours or so on the airframe, I noticed that my wing tips were cracking around where the rivets for the nutplates were.  Though I used "soft" rivets for those and took care not to over squash them with the squeezer, it seems that didn't help mitigate what ultimately happened.  

Plus, back in 2016, I dropped one of the tips in the kitchen, which caused a very large cracked area as well as two others.  Below shows the larger cracked area.

So I removed the tips from the plane and brought them home.  My plan was to drill out all of the nutplates, bond in an additional layup of fabric and install new nutplates.  Then I could fix the gelcoat cracks.

To make my life easier, after removal of the nutplates, I inserted screws into the holes and taped off the holes.  This way my new nutplates could be aligned to the right locations and the epoxy from the layup wouldn't push out further than the flange of the wing tip (left).  In the right image, you can see a layup applied with peel-ply.  It didn't have to look pretty, since it's on the inside.  It just needed to serve its purpose.

  

With the peel-ply removed (left), there was some filing work to do (right), then drilling and countersinking for the new nutplates.

Next it was time to fix all the cracks.  I marked where the cracks were with a marker (left), then removed the gelcoat down to the original layups with the Dremel (right).

I used Evercoat polyester gel paste, which is appropriate for the material composition of the wing tips. 

It's a two part affair (left) and a surprisingly aggressive exothermic reaction upon mixture (right).

After working it into the cracks, I applied wax paper to get a smoother finish (left).  Removal of the wax paper demonstrates the hours of required finishing by sanding (right).

Following sanding, it came out pretty good (I neglected to take pictures of the areas at the nutplate rivets).  I used 80 grit to get it close, then 200 to get level, then 400 and 600 to get a nice sheen.

Installed on the aircraft, the "injury" to the tips is apparent, however when painted it will be unnoticeable.

I actually did three attempts at fixing the bigger crack (always seems to take more than one try to do anything with this plane).  Here's the final result.  Running your hand over it, that there was a crack is imperceptible.