I know exactly what you're going through. When I did my wings, pr= imer=20 seemed like it was not going on thick enough to fill the deeper areas but mi= cro=20 was too difficult to sand out smooth. I used small amounts of body fil= ler=20 on those in-between areas. Things are more complicated on your=20 IV-P compared to my ES since your fuselage is going to blow up like a=20 balloon and is much more susceptible to cracking of the bodywork.

When I do micro I mix it really dry, so it hardly holds together. = I=20 wet out the surface and then go over it with a paper towel to remove any exc= ess=20 epoxy. Too much wet-out will soak into the micro and make it wetter, t= hen=20 it's tougher to sand. I wet out several inches outside of the area whe= re=20 I'm going to put the micro. That extra epoxy sort of protects the prep= reg=20 from sanding. The really dry micro won't spread very well, so get it c= lose=20 and grab a heat gun, warm it up and is spreads like butter. Really dry= =20 micro tends to have a lot of pinholes in it.

I like to think that micro, even micro with a small amount of flox is t= he=20 way to go for contouring. Some of the other off-the-shelf products lik= e=20 Feather Fill work very well too. You'll go crazy trying to get micro (= or=20 other products) perfectly straight. It doesn't feather like primer doe= s=20 and you can beat up the prepreg if you try to feather it too much. And every= =20 batch of micro is a little different, and sands a little different. I=20= like=20 the idea of just loading on the micro and getting it on the first try. = =20 Micro, sand, micro, sand, etc. is harder.

The primer is the best way to get the bodywork straight. Since=20 primer, micro, and carbon fiber all sand at different rates, I really think=20= you=20 need to really load on the primer, 2 or 3 heavy coats then block sand until=20= you=20 start to get a transparent area in the primer then STOP. Trying to get= the=20 last little low spot with a couple more sanding strokes is were you can=20 introduce wavy areas.

I used small amounts of body filler, Piranha putty, where the primer wa= sn't=20 quite filling, but micro would have been too much. But only very thin=20 builds of body filler. It will shrink, but not really a problem if you= =20 keep it really thin. The nice thing about Piranha putty is it sands ju= st=20 like the primer so it's easy to work with over the primer. I may be wr= ong=20 about the body filler on a pressurized plane.

So don't be afraid to load on the primer. I probably swept up=20 a few hundred dollars of primer dust from my hangar floor before I was=20= all=20 done!

Mike Easley

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