[chevelledude13]

I've covered a large bipe with Koverall, a couple of coats of nitrate dope, and then some red butrate dope. I then decided that I wanted to hide the weave in the Koverall cloth, so I mixed up some more red butrate, some dope thinner and talc powder. I brushed it on and it came out pretty nice, EXCEPT there are cracks in the dope finish. It looks like how dirt looks in a field that has not seen rain in a long time. I put a second coat of the butrate dope and talc mix on it hoping that I would fill in the original cracks. Nope...just new cracks. What now?
Help please!
Thanks.

[JimMcIntyre]

How old is the dope you're using? This is an all too common symptom of using using old dope.

some things to try;

Look for a product known as Brodak's "Rejuvenator" ( http://www.brodak.com/shop_productde...ProductID=6799 ). This stuff works miracles on old cracked dope finishes.

Next time try adding a couple drops of castor to you nitrate. This will 'plasticize' the dope and prevent cracking of the nitrate layer. Unfortunately it's too late for this at this point unless you want to start over.

Add retarder to your butyrate to slow the drying to allow moisture to escape (prevent blushing and cracks). This is especially important in humid environments like here in S Ontario.

Hope this helps.

[luv2flyrc]

To add to what Jim said , paint "crackling" is usually caused by one of two things:

Excessive thickness of the top coat or undercoat and\or
Insufficient flash time between coats.

unfortunately, the only fix is to completely remove the old finish and start again

Mike

[JimMcIntyre]

Good point .. I'd still try the Brodak before starting over.

[roscoe]

Just curious, but how much talc did you add to the butyrate dope?
Normally, the dope/talc mixture is used as filler on balsa structure, after a couple of coats of dope to seal the surface, not on a fabric surface that is alraedy covered with pigmented dope. ( my humble opinion, not to be taken as gospel)

[chevelledude13]

I don't think the dope is too old since I bought it from Hobby Hobby this year. It is Sig. If the cracking could be caused by applying the dope too thick then that is likely the problem. When I mixed up the dope I used 1/3 red butrate dope, 1/3 dope thinner and 1/3 talc. It ended up being a pretty thick mix that I brushed on very liberally. I've sanded off most of this thick layer but I can still see a bit of cracking. I don't want to sand much more for fear of going through the Koverall. I was going to try spraying a few light coats of dope now to see if the cracks will fill in. Hope this works.
Thank you so much for taking the time to try to solve my problem Jim, Mike and Roscoe.
Andris.

ps. is removing doped Koverall difficult...I'm tempted to strip it all and start over.

[JimMcIntyre]

Wow! that is thick.

I generally thin 50/50 and even thinner when adding talc. BTW, be sure to use plain talc, watch out for the stuff with added perfume etc. I had a nasty experience with that (last time I had to remove covering).

... and yes it's difficult.

Best of luck however it turns out.

[chevelledude13]

I gave up and stripped the covering off the plane. I sure was impressed with how nicely the dope bonded the koverall to the balsa...this is a great system...shame i screwed it up. I may use Super Shrink Coverite, 21st Century fabric or try Koverall again for my next attempt. I attached a photo of what the real plane looks like.