Has anyone else noticed that corn starch works much better for filling a carbon covered surface than that zinc stuff.. My box of corn starch went away during an ordeal involving our dog and a skunk so my last two finishes were done with zinc stearate because that's what I had..

Really didn't think much about it, just thought it was something I was doing but I fought pin holes like never before and it just seemed like it took a million coats to fill. Actually on both ships (if you look close) you can see where it really didn't fill even after 5 or 6 coats of filler and associated sanding.

Approaching the finishing stages of the new ship started me thinking, I sure don't remember having any big problems with plain old Brodak butrate clear and corn starch.. Going to renew my corn starch supply and see if my memory is correct.

I am starting to think the zinc stuff is fine for spraying on to help fill silkspan but corn starch has it hands down over carbon..

All the matt I've purchased came from Aerospace. Have heard about the sizing issue but doubt it had anything to do with my problems as the airplanes I finished before used the same carbon.

Bob,
So maybe I missed the original point----these pinholes you have now are a new issue --something presumably to do with a new finishing technique?

Only difference was using zinc stearate rather than my usual corn starch (mixed in clear dope for a filler).. Just wondering if anyone else has noted how much better corn starch seemed to work over carbon.

That cinches it for me... Put first coat of corn starch filler on the flaps this morning and just sanded one down.. One coat and it's almost ready to paint, did find two pin holes but thats nothing compaired to the hundreds I had to deal with using the zinc stuff. I sure don't understand.. Read many posts of guys using Nitrate dope and zinc stearate without issues and even swearing it works (fills) better than butyrate.. I sure haven't found that to be the case. My worst finishing nightmare was trying nitrate dope and now I'm completely convinced Corn Starch is the best thing going.

Doc, the only reason I moved away from talc was weight, corn starch is a little lighter and I feel it sands much easier. I don't really have a recipe, just start adding corn starch till it looks right.

Thanks Phil, I was not aware of the details. Good to know tidbit..

Kinda confirms my conclusion that zinc stearate works very well over silkspan but not worth a hoot over carbon. Carbon matt is pretty coarse and does take more filler than silkspan. I don't feel the weight difference is an issue. Might be if you were covering every square inch including the wings but just the fuselage and flaps might cost a quarter ounce if that.

Might be interesting to see what a mixture of the two would do..

If you are using carbon fiber for stiffness, take Al Rabe's advice and use thinned epoxy finishing resin to glue the carbon down first.  Carbon and epoxy is much stiffer than carbon and dope.  Dried dope is just not a very strong or stiff plastic, while epoxy is about 3X as strong as stiff.  The carbon can only do its work if it is held solidly in place.