I bought some Randolph non Tautening Nitrate dope but it still shrinks way too much on my lite structures. any thoughts? I even add some castor oil to try and reduce the shrinkage.

I emailed SIG and was informed that the Butyrate Lite-Cote is the least shrinking. Any experience? Vs. Nitrate non Tautening from Randolph?

Lite coat is preferable on smaller models (ff and park flyers) because it shrinks less. Thin it a bit.

I have a quart of it and have had it for years but have never used it. I have been using the Randolph non tautening Nitrate, but it still shrinks way too much.

I've never had a shrinking issue from any kind of nitrate dope. What are you using for covering? How light a structure are you working with? I've had fabric tighten so much it pulled huge warps in very lightly build wings.

carl

I'm using SkyLoft and the structure is not that light. That is why I am so surprised at the shrinkage. 4 coats of 50/50 non tautening Randolph Nitrate.

ALL dopes, used on light weight structures (anything FF, generally, but I do it EVERY time) should be typically thinned by 50%, as it comes from the manufacturer's container, before it is applied. The smaller/flimsier the structure, the more thinner added. With practice, it is possible to judge appropriate consistency and shrinkage. When in doubt, ADD thinner!

Advertised as such, "non-tautening dopes", does not mean it wont shrink ! I fully suspect that Sig's Lite cote is simply Randolf's non-taughtening butyrate, or perhaps from Certified. It will tighten, as you are finding out.

Generally, nitrate products are loosely assumed to stabilize/stop shrinking rather quickly after application. Butyrate never truly quits shrinking over its service life. Neither is permanent. Both "move" over the hours, days, weeks, and years, as they gas off, get brittle, etc.

With care, both will provide adequate shrinking and sealing properties, appropriate for reason chosen. For modeling use, butyrate is considered fuel proof, but that's not an absolute, either. BTW, butyrate will cover(fuel proof) nitrate but nitrate will not go over butyrate!

Thinned dope, applied in quick drying successive brush coats, builds up a shiny, smoother, sealed finish faster and better than fewer, thicker applications.
Spraying dope with airbrush or small cup gun will build a finish, but takes longer.

I tend to stop applying dope coats based upon reaching a desired finish, rather than a rote "number of coats". Typically, 5-6 coats of clear on tissue is considered adequate for FF gas finish, but perhaps only 1-3 coats on a P-nut? Silkspan or Silk may require more etc.By all means keep track of dope consistency and number of coats applied, when starting out, etc. It will form a basis for your own experiences and preferences.

I haven't posted here for a while but have done some more experimentation since the last time I have. What I have decided is that I will use the Nitrate dope to seal my synthetic covering materials with one to two coats of thinned 2:1 this will not seal my covering material but I will than do that with Acrylic based varnish. This should reduce the shrinkage while providing the sealing of the material. I will be using Pellon- 830 or Pollyspan. The Pellon is more multi directional than the Pollyspan and less heat shrinkable but the weave is less porous and smoother so it fills faster. I will than use Aero-Crylic model aircraft paint for the final color finish. This is the new process I will be using for my small 1:12 scale models. The larger 1:6 scale models will not be so critical when it comes to tautening. Here is the post on the Pellon, https://www.rcgroups.com/forums/show...Is-it-possible