Butyate Shelf Life or Useful Mixed Life

[Serge_Krauss]

This is related to my other post on silkspan, but concerns dope's adhesive qualities for silkspan. I suspect that my problems may be apparent through this description, but I haven't encountered this before. I have kept my current dope can closed tight for several years, filling jars 50% with Brodak's clear Butyrate, 50% with Brodak thinner and then adding thinner when needed to keep the brushable/sprayable consistencies needed.

On this project, I have a wing that I stripped of faded and damaged covering with Dad's stripper, as recommended by Randy. It all came off well, but there was residue left. I sanded it briefly to smooth it and brushed on three coats of clear butyrate. When I tried to silkspan the upper and lower surfaces of the outboard wing the pictures illustrate what happened. It took a lot of work to get the silkspan to adhere, and the next morning, three areas had come loose. I spent hours pulling out the wrinkles and reattaching the silkspan, making a real mess of the lower tip, which I then recovered with some difficulty. Since then, I've tried to build up the dope around the periphery of the wing, but in two places, the silkspan seems to have slipped, letting in minor ripples.

Concurrently, I applied dope to the periphery of the uncovered wing. The dope was absorbed in many places, but puddled and remained sticky and shiny for upwards of 24 hours in others. This has never happened before, drying time to a dry feel usually being just a few minutes. I tried applying thinner to these places, but that did no good. So I wiped them, leaving sticky areas that finally set, close to dry.

So, I'm wondering whether my technique has been wrong or if dope loses its chemical properties with age. I don't understand the immense drying times. In all my life, I don't think I've ever had a wrinkle in silkspan after it dried. But, I've never used dope this old with modern-ish silkspan.

I have an experiment going now, where I am applying 3-4 cotes of clear butyrate from an old, but unopened can to a piece of balsa. I'll then try to attach sample pieces of white (undyed) plyspan (not polyspan) and old (real) heavy-weight silkspan by brushing on thinner and by brushing on the 50/50 dope.

SK

[Serge_Krauss]

'sorry, I hit "Quote" instead of "Modify."

[Clint Ormosen]

Wow, that was quite a mess you had going. This is one of the reasons I like nitrate dope for putting down covering. It's sticker.
Couple of causes for this I can think of. Either there wasn't enough dope down on the wood prior to covering, or too much thinner in the dope. Dope that's a few years old should be ok if it was sealed tight. Ten year old dope might be too old, but you didn't say exactly how old it was.

[Serge_Krauss]

Thanks, Clint. It is actually probably one of several cans I bought sometime around 2003; so its pretty old. It comes out of the can a bit yellowed.  That's one reason I'm experimenting. I just opened the last can tonight to try it out on the two kinds of silkspan. I'm kind of afraid to dope the wing shown for fear of the silkspan coming loose. If the trial started tonight works, I may remove what I already put on and re apply...again.

SK

[Clint Ormosen]

Thanks, Clint. It is actually probably one of several cans I bought sometime around 2003; so its pretty old. It comes out of the can a bit yellowed.  That's one reason I'm experimenting. I just opened the last can tonight to try it out on the two kinds of silkspan. I'm kind of afraid to dope the wing shown for fear of the silkspan coming loose. If the trial started tonight works, I may remove what I already put on and re apply...again.

SK

That might be the safe play. You don't want to get halfway through a finish and have the covering come loose.

[billbyles]

Serge,

I have been using Randolph butyrate dope left over from my full-scale aircraft restoration shop that is over twenty years old and it is still working just fine.  It sounds like your problem has to do with contamination  left over on the wing from, I suspect, the stripper since the "stickiness" is spotty and not all over.  To dry the dope has to be able to soak in to the balsa.  I don't use Brodak dope but it is just butyrate so it will react the same to contamination as Randolph butyrate dope (or any other butyrate dope)will.

Bill

[Joe Connelly]

Serge, I think Bill is right that the problem has to do with the paint remover. Balsa is great at absorbing whatever liquid we put on it. Most paint removers were meant to be used on metal or hard wood surfaces. Those surfaces could then be cleaned up with thinner,denatured alcohol, or prepsol. Why don't you try your butyrate dope and tissue on a separate balsa surface and see if it sticks it down on a test surface? If it does, I would try wiping down the plane with thinner and let it dry completely.

Joe

[billbyles]

<snip> but Nitrate works better for applying silk or silkspan. 

I'm not sure what you guys mean by "...nitrate works better..."  I have always used butyrate from the bare balsa on out through the final clear topcoats and have never had a problem with adhesion.  I think this has become one of those "folk legends" rather than anything substantive.  Some of my airplanes are twenty years old and show no signs of delamination of the silkspan or butyrate topcoats.

Some of the older STCd covering systems for full-scale fabric covered airplanes require nitrate dope as the first coats down on the fabric but that has little or nothing to do with applying or finishing silk or silkspan on our models.  Nitrate dope will shrink more than butyrate but nitrate has a lower tensile strength, so I have seen cases where the nitrate will begin cracking sooner than butyrate due to higher surface tension along with lower tensile strength.  So, I guess if you are convinced that you must use nitrate for your models then that's what you should do.

[Bob Reeves]

I'm not sure what you guys mean by "...nitrate works better..."  I have always used butyrate from the bare balsa on out through the final clear topcoats and have never had a problem with adhesion.  I think this has become one of those "folk legends" rather than anything substantive.  Some of my airplanes are twenty years old and show no signs of delamination of the silkspan or butyrate topcoats.

Some of the older STCd covering systems for full-scale fabric covered airplanes require nitrate dope as the first coats down on the fabric but that has little or nothing to do with applying or finishing silk or silkspan on our models.  Nitrate dope will shrink more than butyrate but nitrate has a lower tensile strength, so I have seen cases where the nitrate will begin cracking sooner than butyrate due to higher surface tension along with lower tensile strength.  So, I guess if you are convinced that you must use nitrate for your models then that's what you should do.

Agree, first and last time I tried to use nitrate I ended up with silkspan that looked like a prune. Ripped it off and reapplied with butyrate, turned out like expected. Gave what was left of the nitrate to a friend that liked it. Butyrate works fine so why bother..

[Serge_Krauss]

Thanks for all the input, guys. I think you're right about the stripping material, although none of the previous users mentioned what they did after removing the original coverings. I just finished my little butyrate dope trial. I applied four normal 50/50 coats of butyrate dope to a scrap piece of balsa and then attached pieces of Sig plyspan and old heavier K&S silkspan with one brush stroke of straight thinner alone and one stroke of clear butyrate (for 4 samples), each from the newly opened can of decade-old stock. The silkspan and plyspan each adhered tight in all cases.

The wing has gained almost 1/2 oz of weight during my application of plyspan to one half-wing plus three+ coats of clear to the other side. So it looks like I should remove all the old material from at least the uncovered side and apply covering with the fresh old dope. Your input has been greatly appreciated.

SK

[Clint Ormosen]

Well, I'm one of those guys, I guess.

Although Ive never really encountered any specific problems with using all butyrate, I still have an easier time of it using nitrate on the wood and then sticking down the covering with it. Just seems easier to work with and since nothing bad has happened because of it, I'll continue to use it. Some say it shrinks more, some say less. I haven't really noticed much shrinkage difference between the two. I also get no cracks and such from it, at least not yet.


However, I feel differently about putting crap like baby powder and cornstarch in the dope. I see no reason at all for it and constantly read about finishing problems from some of those that do it.

[billbyles]

Well, I'm one of those guys, I guess.

Although Ive never really encountered any specific problems with using all butyrate, I still have an easier time of it using nitrate on the wood and then sticking down the covering with it. Just seems easier to work with and since nothing bad has happened because of it, I'll continue to use it. Some say it shrinks more, some say less. I haven't really noticed much shrinkage difference between the two. I also get no cracks and such from it, at least not yet.


However, I feel differently about putting crap like baby powder and cornstarch in the dope. I see no reason at all for it and constantly read about finishing problems from some of those that do it.

When I have used talcum powder in the past (I don't use baby powder due to the additives such as perfume & skin conditioners included) the only time I encountered problems was when I overloaded the dope with the talc.  This led to small cracks showing up in the surface of the filler coat because of insufficient dope as binder.  The other thing about using talcum powder is that it is heavy; you need to be sure of getting it sanded off except for the flaws you are trying to fill.  A much lighter way to go for the filler coats is zinc stearate - it is a much lighter material and takes much less of it mixed into the dope to get the same fill as talc gives.

I suspect that the problems with using cornstarch also stem from overloading the dope with it.

[Clint Ormosen]

When I have used talcum powder in the past (I don't use baby powder due to the additives such as perfume & skin conditioners included) the only time I encountered problems was when I overloaded the dope with the talc.  This led to small cracks showing up in the surface of the filler coat because of insufficient dope as binder.  The other thing about using talcum powder is that it is heavy; you need to be sure of getting it sanded off except for the flaws you are trying to fill.  A much lighter way to go for the filler coats is zinc stearate - it is a much lighter material and takes much less of it mixed into the dope to get the same fill as talc gives.

I suspect that the problems with using cornstarch also stem from overloading the dope with it.

All True! I also think thats the cause of the adhesion problems associated with it. Either that or guys aren't getting the wood clean enough after sanding the talc off, then trying to paint over it.

I avoid the whole process. Seems like a whole bunch of hassle/risk to save a coat or two of clear dope. 

[Balsa Butcher]

I had similar problems the last time I used "modern-ish" type silkspan. It seems to have adhesion issues compared to the older stuff. It also does not shrink as well, gets loose every time you put a coat of dope on it and is not as as strong as the old stuff. This may be part of the problem.

[Clint Ormosen]

I had similar problems the last time I used "modern-ish" type silkspan. It seems to have adhesion issues compared to the older stuff. It also does not shrink as well, gets loose every time you put a coat of dope on it and is not as as strong as the old stuff. This may be part of the problem.

A good arguement for the use of Polyspan. But now I'm hijacking the thread.

[Brett Buck]

When I have used talcum powder in the past (I don't use baby powder due to the additives such as perfume & skin conditioners included) the only time I encountered problems was when I overloaded the dope with the talc.  This led to small cracks showing up in the surface of the filler coat because of insufficient dope as binder.  The other thing about using talcum powder is that it is heavy; you need to be sure of getting it sanded off except for the flaws you are trying to fill.  A much lighter way to go for the filler coats is zinc stearate - it is a much lighter material and takes much less of it mixed into the dope to get the same fill as talc gives.

I suspect that the problems with using cornstarch also stem from overloading the dope with it.

    This is the same problem that you can get using Windy's technique of allowing the pigment to settle, then pouring off some of the clear to concentrate the color. There's so little binder left that if you get an excessively wet coat of clear, it all bleeds through or cracks. Obviously he can get it to work but in less than master's hands it can be a real mess.

    This is also why epoxy seems to cover better while being lighter. The epoxy base can hold incredible amounts of pigment. Some colors of Klass Kote (like white) come out the can with the consistency of pudding, but it has no problem sticking together. Its very heavy per unit volume, but it only takes a tiny amount of it to be opaque, so it winds up lighter than an equivalent dope  finish.

     Brett

[Serge_Krauss]

Very informative contributions, guys! I've found the same adhesion problems with new stuff and have been using other things because of that. After Ted's problems with dyed "plyspan," I was reluctant to use plyspan again, but he had right after I had applied it. My plane didn't have a long life, but I verified that the stuff fades badly. I did not get any of the splitting I'd read about though, and have used it again, because it went on OK and was old stock, resembling the old medium silkspan. I used a couple pieces of white (undyed?) this time, with the adhesion problems mentioned. My little trials seem to indicate a problem with the dope and stripper residue.

I completed experimenting last night by trying to attach some old (real) silkspan trial strips to the uncovered half of the wing. I was surprised to see that my newly mixed 50/50 dope (from previously unopened 12-year-old can) and thinner alone both attached the silkspan pretty well. Compared to the trial balsa strip, the attachment may have been a little less tight, and the thinner did not seem to be working well at first. However after a night of drying out, both stuck the material on very well. So, the problem seems mostly the previous aged dope mixture.

Picture below shows the various tabs labeled "Thinner" and "dope."

SK

[Serge_Krauss]

I think I've done enough different things now in re-covering this veteran wing to know what was wrong, and it matches up with advice given here (thanks again!). I mixed up new 50/50 solutions from a just-opened can of decade-old Brodak clear, and it attached some older-style K&S silkspan very nicely. The tips again proved difficult, because there was only a little area to attach the silkspan, and reapplication loosened the material, allowing wrinkles to creep in as I applied silkspan to the opposite side of the panel. That had not been a problem on first-time builds. So...

1) Residue from stripper compromises adhesion of new dope.

2) Constantly adding thinner to dope that has thickened through evaporation seems to compromise it's adhesion.

I'll have to be careful of those tips, and next time(?), I'll use some acetone and sand a bit before reapplying silkspan.

SK

[Larry Borden]

I se nitrate to fill the wood and then to adhere silk or silkspan. Switch to butyrate the rest of the way. I use Randolph dope since I can buy it cheaper from aircraft supply company locally. Randolph supplies Brodak.  I use Brodaks Crystal Clear as the final coats.
I ran into a problem when applying pink Royal silk to a Ringmaster that I helped my wife build. It took for ever to fill and tighten up. I was ready to take the silk off and re-cover using Dharma silk. I did a search and found out others had the same problem. It was Thai silk, don't know what the difference in silks are, but it finally tightened up. I had never had that problem before.
As far as using nitrate and butyrate. Nitrate can not be put on top of butyrate, but I figured you know that and I threw it in for free. lol

Love the smell of butyrate dope in the morning.

[Serge_Krauss]

Thanks, Larry. Yeah, I don't understand why absolutely No one in my family likes he butyrate smell. 'course, now that I'm on application ten, I'm getting a bit tired of it myself, although to me, the faint smell of butyrate dope in my work area is pleasant and reminds me of good creative times.

[Larry Borden]

Used to drive my parents crazy when I would dope a combat plane in the house. Show you how smart I was, I would even hold the wing over a gas stove flame to speed drying. It's probably a miracle I'm still here. People come into my shop after I've been doping a plane and it nearly knocks them out. I tell 'em. now you know why I'm like I am. Years of smelling the stuff. Still love doing it old skool.
Oh and they have invented this new stuff, called sandpaper and it comes it different grades. Wish they had made that years ago. lol

[john e. holliday]

The plane looks great.  I too used to dope in  my bedroom when I still lived at home with the door closed.   Even after I got married and doped in the upstairs room people would come for a visit and not stay long.  Also depending how much you thinned the butyrate would also slow the shrinkage rate.   On silk never had any problems, it was nylon I had problems with until I was told nylon does not shrink, you have to  put it on tight.   The poly-ester cloth I use every so often does not shrink up until the last coat or several days after the last coat.   The first few coats, you think what kind of mess am I making.   A Monokote irom will shrink poly-ester until the dope is applied.   Thenit is jut keep putting on clear dope until sealed.   It will be be drum tight as time moves on.

[Serge_Krauss]

My memory seems to be going: I cannot remember brushing on as many as thirteen 50/50 and heavier coats and not being finished with clear! I want to just clear-coat this wing (or perhaps add some dye for a translucent effect) and add trim, but I've just run out of Brodak thinner and don't yet have the gloss I want. I do have a nice new warp that is mostly, but not all, removed. Well, thiese are the surface textures after 13 coats (+1.7 oz) of Brodak clear. The last coat was the only one that was nearly unthinned. It added .35 oz after 16 hours of gassing off.

Do you guys put on this much clear? Thanks for the responses so far!

SK

[john e. holliday]

Usually after 8 coats I'm done with clear.   The only way I can get a high gloss is with two part automotive clear.   I don't think todays dope is the same as it was when we had Testors.

[Larry Borden]

I keep brushing clear over silk until it's glossy or I get tired of doing it, whichever comes first. lol  I use Randolph dope exclusively except for the final clear coats. I use Brodak's crystal clear to bring out the gloss in the colors.

[Bill Little]

I am the actual "Blind Hog" that does grub up an acorn once in a while.  I have been using tinted non tautening Randolph Nitrate for the base coats and to adhere all coverings.  Once I have the open bays covered i move to tautening butyrate to shrink up everything real tight.  Last is non tautening butyrate for filler/final coats.

I cannot argue with the results Bill B. gets, he truly is an expert in using dope as he has made a living using it for real for decades.  But, my system does work and lasts for at least twenty years as that is the oldest model I have using this method.  Oh, yeah, my filler is zinc sterate in non tautening butyrate.

BIG Bear
RNMM/AMM

[Serge_Krauss]

Thanks, guys. Here's where I am, and it appears that no matter how well I planned and tried for that relatively light model, I just manage to make it heavy.

So...end of evening. After giving the last wing coat some 30+ hours to "gas off," I again pre-assembled the wing, fuselage, engine, and tank and brought up most of the remaining hardware to weigh. I still want a 35-oz model. The weights:

1) Balsa and silkspan (13 coats) airframe + engine + tank: 27.5 oz.
2) 10" x 4" Prop: 1.05 oz
3) Control Rod: .55 oz....
4) Landing Gear (2 struts, 2 wheels, 2 bolts): 1.60 oz.
5) Package of 6 4-40 screws: approx. .1 oz (not weighed separately)

All weighed Simultaneously: 30.8 oz

So I have to finish this thing, fuel-proofed and preferably attractive, on 4 oz or less of finish coatings. I build too heavy...

Edit: Oh, and the weight is not in the weight box. Arghhh...