Polyspan & Brodak Dope

I am interested in hearing from those who have used Brodak dope and Polyspan. This is my first time using Brodak dope and so far doing the tissue on the solid parts of my Cardinal this stuff is excellent. The Polyspan will be a new experience as well. What is the recipe for success with Polspan and Brodak dope?

I've used Brodak's and I've used Polyspan but not together. Knowing how Brodak's is I'd predict excellent results, just be carefull not to sand through the dope into the span, the fuzz will drive you nuts. Polyspan doesn't do compound curves well either, so don't expect to be able to do something like a Spitfire with it the first time.

I have used Polyspan and Brodak before it works well if you follow these littel tips I got from Windy. It is said in the instructions to use only nitrate. Nitrate does not have a gloss hardener in it so it will penetrate the polyspan. Butyrate is a hardener dope and will not penetrate but here is how you get around it.

First where you are going to use Polyspan you will need to put down an extra coat of dope. If you normally cover with two 50:50 coats of dopen you will use three. I usually use four coats where I am going to use polyspan.

After the dope is dry say a day or overnight. Sand it lightly with 320 and get it smooth but dont cut it all off.

(Windy tip right here)Now mix up some dope and thinner 90% thinner and 10% dope. You could use all thinner if you wanted but I throw in a little dope. The thinner will penetrate andd reactivate the dope underneath the paper and it will stick no problem. A 50:50 mix will not penetrate as well and take many more coats to get it to stick. With the mostly thinner mix it sticks down with one coat.

I stick it down around the perimeter. Then I hit it with a hair dryer and it shrinks as it dries. Then I put the the mostly thinner mix all over the covering and let it fully dry over night.

Form there I move to 50:50 mix thinner and dope. I put down three solid coats on the Polyspan area. The dope dries fast so this application can be ready for sanding to finish in just a few days.

The FUZZ bites for sure. If you notice when you start to sand out that you are getting fuss as you sand stop and apply more dope. It is not like silkspan where you can sand it out. It is backward. You will get the fuzz around the edges but with a little dope on there and sand elswhere while it dries you can
get a smooth STRONG covering. I love it and wouldnt want to use anything else.

I once bent over my plane and my battery fell out of my pocket and just bounced off the open bay. It was quite scary but there was no damage. If it had been silkspan it would have been bad.

I hope this helps. These are few tips I have learned over the passed few years of use.

DMOON, I think you indicate here that you use Butyrate not Nitrate dope. correct? Thanks, Jerry

Yes that is with Brodak butyrate dope. I have finished with both kinds of dope and the above is how I did it with Brodak.

Another tip. You will encounter situations where no amount of dope, however it's applied, will adhere the Polyspan to your framework. Usually this happens around the tips or along thin trailing edges. Use Sig-Ment, applied full strength or thinned slightly to brushing consistency. Press the Polyspan in to the wet cement and hold until it sets.
Whenever you use Polyspan, be careful not to rub it too much as you stick it to the framework. Excessive rubbing will abrade the material and raise its nap.

Derek Moran

Interesting question as I used them both for the first time on my Cardinal. Make sure the polyspan goes down shiney side up. You have to look carefully to see one side is duller than the other. Tom Morris sends his with green dots on the "up" side. Like Mr. Moon said, coat the wood with three or four coats of Nitrate, not butyrate. Use the 90/10 mixture or straight thinner to apply the ply. It is water proof so it goes on dry. Be sure to pull it as tight as you can as you dope it into place. It does not have a "grain" likle silkspan or silk. Once it has dried, do another coat of thin dope. After one day, use a hair dryer or plastic film heat gun and CAREFULLY (caps for emphasis, not yelling) shrink the poly tight. It will get tighter when you dope it with butyrate. Brodaks and Sig are the only two I now use. When the Sig is gone, only Brokdaks. It is thick and needs to be reduced with their thinner, and it goes a looongg way.
As to the tips, I used silkspan. When sanding, do so only after three coats of dope are into the fiber. I use the 3M sponge pads on the poly, fine and superfine grades. Spray after three thin coats of clear hve been applied. I always add 10% retarder to my dope, high humidity, and it helps the new coat to penetrate and lets the dope really settle flat. You will love the Cardinal. Great flyer and even at 50 oz and a good .40, no sweat.

Hmmm? This thing is sooo sllooooww this morning, I didn't think my first message went through, so I repeated mahsef. sorry.

Interesting question as the first time I used them was on my Cardinal! I am assuming you don't know a few things, so please don't take offense if I state the obvious. First polyspan is water proof and goes on dry. It has no grain as does silk or silkspan. It has an up side and a down side. The up or top side is shiney, the bottom is dull. This is not easy to see. I got my polyspan from Tom Morris and he puts little green dots on the up side. If you put it on upside down, fuzz city big time. It will fuzz up if you dand too hard. Use silkspan for the tips. Apply it like Mr. Moon states, three or four coats of Nitrate, not butyrate. Pull it as tight as possible, just don't overdo it, as you apply the thinner to the polyspan. Let it dry at least 24 hours. Use a hairdryer or plastic cover dryer and be very CAREFULL (caps for emphasis, not yelling) when applying heat. It will run like a nylon stocking if it gets too hot. Guess how I know this. Just take your time. Once it is fairly tight, brush on a thinned coat of Nitrate. Let it sit overnight. Then do the same two more times. Do not sand these coats, but lightly run a 3M sanding pad, super fine grade, over the third coat. After these have dried for two days, spray on a coat of Butyrate, 60/40 clear to thinner, with a few drops of retarder added. This doping will cause the polyspan to get tighter, but it never gets so tight as to cause problems. Spray on two more coats of clear, letting each one dry overnight. A
final light sanding and do your thing with your colors.
My Cardinal came out at 40.8 oz the first time. It flies great. With repairs, engine and tank swaps, it now weighs 44.6 oz. I have been told by four other Cardinal fliers that even at 50 oz, and with a good .40 it still flies great. I belive this profile will be the Magician or Ringmaster of this era in stunt.

Thanks for all the the advice. The Brodak dope is simply fantastic. I will try to get the 3/4 precoats on this week and attach the Polyspan next weekend. I like the idea of not needing to apply water onto my nice straight wing.

LAST EDITED ON Apr-09-02 AT 09:38 PM (CST)

LAST EDITED ON Apr-09-02 AT 09:36 PM (CST)

Just wanted to add a few things on this thread to help with polyspan. I did my Cavalier for VSC with Polyspan and was very happy with this product. I agree with the thin mix to adhere to the wood but I shrink the covering right away while also drying the dope used to glue it down. I also cover the tips with polyspan. Heat not only shinks the material but it also relaxes (makes it stretchable) it to form around corners. Use one piece long enough for the entire wing quarter(top half etc.) but glue it down at the last rib and leave the tip to work on later. Make sure it is LONG enough to give you enough material to grab onto to pull over the tip while heating and shaping.Even if you have to make a slit to take up the slack it is not a problem. Now as to the fuzzies from sanding too much, just fix with CA. Use thin CA and wipe area with paper towell and sand with 220, no waiting, and the area is hardened and no more fuzzies(at that spot) to deal with. I use a little more heat than a hair dryer can provide. I use a Monocoat gun. You need to get all of the shrink out of the material so it stabilizes to the final setting, but do not over do the heat.
Richard Oliver