I'm now surfacing and sanding the plug. I use polyester resin mixed with "Q" cells and "wax in styrene". This is brushed on and sanded with 40 grit paper dry to start with. After first couple of coats or so, I then wet sand between coats with 80 grit wet and dry paper.

This is in preparation for spraying with polyester gel coat.

My recently built PW51 plank has flown many time now and is such a success that I am developing the plug to include the fin and fillets. I'm make a new mould from this. The final model will be a 2 part wing, my first.

The pictures tell the story, but a few details might help to explain how I went about it.
I made the fin by hot wire cutting a symmetrical (SD8020) blue foam core and gluing pre made skins onto it in the usual fashion. Wooden tips and LE were then added and shaped. I then PU glued it to the old plug.
For the wing fillets I went about it like this: I printed out several profiles of the airfoils on Profili2 and cut some 10mm thick Douglas Fir to the shape. These were glued onto the plug using the jig system in the pictures. I also cut out some formica profiles which are hot glued to the outside of the wood. These are intended to protect the arris on the end of the fillets during the sanding and filling process. To get them square with the fin, a 5mm locating hole was drilled in both sides and a larger one drilled through the main body of the plug to take the 5mm carbon tube. Everything was set up on a level surface and a plumb bob was used to get the fin/body vertical.
I also used the tube to ensure the fillets were square to the centreline of the body.
The last thing to check was that the fillets were parallel.
The two sandwiching boards clamped the assembly and were adjusted to be both parallel with each other and parallel with the centreline.

I then cut some small LE and TE gussets out of some 1.5mm ply. These were glued in to provide screeding stops for the splooge infill.
The last picture is the polyester/"Q" cells/wax in styrene filler roughly applied waiting to go off prior to sanding.

Jim.