Another choice I have found that is light and stiffening and durable is West system slow epoxy with their microlite filler. Mix alot of filler so it is a thick paste, then putty the assembled wing. After hardening, I use a random orbital sander and 100 grit paper. I sand until alot of the white foam is visible throught the brown putty. This insures that you have not altered the airfoil. Then I DO NOT USE ANY TAPE. Just one strip over the leading edge. I did this to an M-60. The finished weight target was 28 ounces. My plane came in at 28.5 ounces and has been durable and stiff so far. I do not build foamies any other way, I just re-did my Jazz 60 and cannt wait to get her back in the air!! I redid the Jazz because the first time I followed the directions and the tape stopped adhering to the the foam and made it fly poorly. This time I used the microlight/epoxy and have not flown her yet..though I noticed that, what was a flexible airplane is super stiff now.