I need someone to respond to this post that has experinced the following problem while using silk and dope. About 15 years ago I used silk and dope on a Supersporter 120 everything went ok during the covering but when I applied the first coat of 50% reduced Aerogloss dope the covering relaxed and would not tighten after the dope dried. I assumed it was the Aerogloss dope. About 10 years ago I covered three models a Taurus, Sport Aire 40 and a Trainer 60 all with silk and dope except this time I used Certified Coatings Products butrate dope. I had no problem when I apllied the first coat of 50% reduced dope. The covering didn't even relax. After I applied 3 coats of clear the covering was so tight you could bounce a dime off of it. Now forward to the present. I purchased a Nobler control line model from Tower and removed the Monocote covering. I applied the K&S silk as I did on the previous three models and applied the first coat of 50% reduced dope only this time I used Randolph brand butrate dope. The covering on the stab and one elevator half relaxed and then tigntend up with no further problem. The problem is with the other evelator half and the vertical fin the covering relaxed after the first coat of 50% reduced dope and will not tigten. I applied the silk wet and pulled it tight to remove all wrinkles. I then dope the perimeter and wait until the water dries from the silk. I then take a look to verify the covering is still taught and proceed to apply the first coat of 50% reduced dope. If all goes well I apply one additional coat of 50% reduced dope and then 2 additional coats of unreduced dope prior tho spraying the color coat(s). The temperature in the basement is around 72 degrees with a humidity of less than 70%. My question is what went wrong?

If the covering was applied wet, and all wrinkles were carefully pulled out, and you made sure the grain was nice and straight, you should have had no problems if the dope you used truly was butyrate. Apply the covering wet, and then dope around the perimiter and allow to dry. Usually, properly-applied silk will be nice and taut. When you apply the dope, the silk may relax a bit, but not so much that it's a problem. It should tighten right up when the dope dries.

After the first 2-3 coats of 50/50 dope/thinner, you should not see any change in the tautness of the covering, although butyrate will tend to continue to shrink over time. That's what can cause surface cracking on old butyrate finishes.

If the covering relaxed, did it come loose when you applied later coats? You do have to be careful that you don't cause the silk to unstick when you start to apply later coats...too much thinner in the dope may cause that to happen. Dope never loses the ability to dissolve itself, so later coats will tend to dissolve earlier coats. If you only have a thin coat around the perimeter holding the silk to the structure, then when you apply later coats, they could loosen the original application you used to stick down the silk. It goes soft, and the silk is now free to move when the dope you apply dries.

Usually, one or two full-strength coats should be applied around the perimeter to prevent this. Now only the uppermost bit of the dope used to stick on the covering will soften, but not enough to cause the silk to loosen.

Bill,

Thanks for the reply. I ensured that all the items you mentioned were done. The covering has not shifted. I will apply one coat of full strength dope to the affected area only and not on the perimeter to ensure there is no loosening of the silk around the edges.

Thanks

Mike

Mike, I recently covered a 1/2a Texaco in silk (my first silk covering in many years). I used nitrate for the first few coats and parts of the covering remained loose. After a couple of weeks, however the silk became taunt. Hopefully yours will tighten as the dope cures.

jess

Thanks for you help. As Jess described my silk tightened a little after about 24 hours. I attribute this to the use of a mixture or 50/50 dope and thinner for the first 3 coats. After I applied unthinned dope the covering became as tight as I would expect.

Thanks again for all the relues.

Mike

Hi; I just read your reply on a dope problem. I am finishing a Penn Valley Quaker and have covered it with vintage solartex.
I would like to spara the entire airframe with Sig dope. Have you had any experience with spraying dope. Sig offers retarder.
Thanks ....Pete

I don't know of any reason it won't work. Dope will go over most anything. I would do two things. Test it on a spare piece of covering and apply the first couple of coats pretty dry to make sure the dope can't soften the paint. You only need retarder when the humidity is high enough to cause blushing. You'll see a milky fogging in the dope. It's moisture trapped in the dope. Wait if you can for a dryer day amd respray. It usually goes away then. If you do need retarder, use the least amount possible, preferably 10-15% max.

you should have no problems. Just procede as kdheath suggested. Make the first few coats light to avoid "puddling" on the inside of the silk.

jess

I have only recently started using nitrate dope in the proper way, i.e. for the early coats. You get much better taughtening than with butyrate, and I find it easier to work with. I have switched to Randolph's, because it's cheaper.

Of course, you still need to finish with butyrate.

I also have sprayed dope with good success. I use a good portion of retarder, and apply thin coats. That prevents the dope from drying too fast, and lets the finish flow. Otherwise, you can get a rough finish.

As for 'puddling' on the inside of the finish, I understood that was necessary to saturate the silk (or silkspan). Dope was actually part of the structure of early aircraft. The canvas had to be saturated to develop its maximum strength. Has anyone else heard that?

One must use a little caution when speaking nitrate and /or butyrate dope. There is taughtening nitrate, and non taughtening nitrate, and taughtening butyrate and non taughtening butyrate. All are sold by Certified and Randolph.

Les

It has been some 20 or 30 years since I used dope but, if my memory is correct (sometimes doubtfull) nitrate dope is what shrinks most, Butyrate has very poor shrink capability and is used mainly to fuelproof the Nitrate. Also, you can not apply nitrate over butyrate but you can do the converse.

For silk, I understand that taughtening is appropriate. Non-taughtening is used for synthetic coverings, as I understand it.

"Snitch" Yopu're right, non-taughtening is for synthetics because they are heat shrunk. But, even non-taughtening dope still shrinks over time. The synthetics are supposed to be saturated because you can't technically get a chemical bond. Ever had the paint come off when you are pulling off trim tape?