I have used the same method of making fillets for many years. They are made from glass (as opposed to epoxy) resin and micro balloons. I mix the MB with the resin to a stiff paste (the spatula will stand up in it) then 'accelerate' the mix with cobalt accelerator until it is slightly pink in colour. Taking about a thumb sized amount at a time mix the hardener in well but quickly, remembering to keep the hardener to the correct ratio for the amount of resin used per piece and NOT the total size of it. After sanding the wood smooth I do nothing more than wipe the area with cellulose thinner before applying the mixture. I apply it using a steel artist's pallette knife and only do one fillet at a time. Any left over is always discarded as normally there is not enough time to finish another one. Besides it's cheap enough and it is best to use fresh mix on each fillet (Mix a smaller amount for the tail and fin - I still keep to the same procedure)Once the material is pushed roughly in place I then smooth the fillet into shape using a 4" long piece of silicone tubing dipped in acetone. This normally takes several strokes but each one must have the silicone wiped and re dipped in the acetone. I never used to mask off the area but now do so on the wing. This gives a very thin edge to bring the tissue up to and is easilly filled and faired in. I normally wipe a finger over the fuselage edge to feather it in. You can either lick your finger or dip it in the acetone -neither is very palatable! In a warm environment this will take about two hours to go off but really needs a day before you are able to sand it. I use 180 grit to start, folding small pieces no more than an inch wide and about 3" long around the piece of silicone tube with the 1 inch along the tube. If the 'tail ends' are held between finger and thumb the paper can be revolved around the tube to give fresh paper to the fillet as it becomes clogged. I do exactly the same for the tail end only using normal sizes silcone fuel tubing to get the smaller radii. By using paper only 1" wide 'dig ins' particularly on surronding balsa are avoided.
I normally finish off with 320 before applying a coat of dope to seal it.
Up until three models ago I was using all nitrate dope and experienced no problems at all with paint adhesion. Consequently, moving over to all Brodak, no thought was given to potential problems in this area. I have since read of delaminating problems with this product on fillets but have to report that this has not been experienced on this material. An Oriental finished well over a year ago shows no sign of a problem and was finished exactly as described.
The model? Well this is now covered and ready for spraying but has been mothballed until the spring. It is an Italian design first seen in an Aeromodeller Annual about 1967. I believe SSW can now supply the plan.
Hope this is of interest to some one somewhere as well as Bill of course
Regards to all - Tug