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Building Tips and technical articles. => Paint and finishing => Topic started by: Jim Svitko on August 08, 2016, 03:59:54 PM
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For those who have used automotive two-part clear coat over butyrate dope, how long did you wait after applying dope before applying the clear?
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Jim,
I thought butyrate colored dope was fuel proof?
Charles
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Jim,
I thought butyrate colored dope was fuel proof?
Charles
Butyrate dope has very little, if any, resistance to glow fuel. Even ordinary rubbing alcohol will remove and stain dope. I use Randolph and Brodak dope and if fuel is not wiped off almost immediately, there will be a blemish.
You might be referring to the old Aero Gloss from years ago. It was, from what I remember, fairly resistant. It was called dope but I heard it was not really butyrate dope. Instead, it was some other product.
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Jim,
I wish I could help you with an answer, and you guessed it, I used to use the Aero Gloss from years ago.
The dope you applied, is it flat or gloss?
Photo of the model?
Charles
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Jim,
I wish I could help you with an answer, and you guessed it, I used to use the Aero Gloss from years ago.
The dope you applied, is it flat or gloss?
Photo of the model?
Charles
I have been using Brodak dope for many years. It, and maybe Randolph as well, does not have much gloss. Some colors have more gloss than others. Some type of clear is needed and I am tired of no fuel resistance. So, on the current project, I want to top coat it with automotive clear. I am about ready to apply the color and I have the automotive clear on hand.
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Jim,
Are you spraying your clear through a spray gun or are you using a 2K aerosol can?
The paint I use, I can clear the same day.
Charles
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The auto clear I have will go thru the spray gun. The auto paint store also has the aerosol two-part clear, the type of can with the valving that allows the activator to mix. But the activator is not "adjustable". That is, there is no slow, medium, or fast to adjust for weather conditions (temperature). The staff at the store recommended that I use my spray gun since at this time of year the slow activator is needed in the hot weather.
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Jim,
All understandable. Glad you have a handle on it.
Post a photo when the model is completed?
Charles
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Jim.
there is no real easy answer to your question, a lot of variables, the simple answer is to wait as long as you can
however thats not very helpfull so , if you have waited a reasonable amount of time between colors and base coats, then I would wait at least a week in warm weather and average or low humidity. Of course you can bake it in your car to help speed it up.
The biggest issue you can have after waiting a reasonable time frame is that the solvents in the clear will soak into the dope and swell it, then after the clear kicks, the dope underneath will dry out shrinking back again and leaving you with very shiny scratches and grain showing through.
so that said, then at the least a week in hot conditions will go a long way to preventing this
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You might be referring to the old Aero Gloss from years ago. It was, from what I remember, fairly resistant. It was called dope but I heard it was not really butyrate dope. Instead, it was some other product.
I believe was acrylic lacquer, with the exact constituents varying from batch to batch.
Brett
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I don't think it is really necessary to cover the whole model in the two part stuff. Just do the nose section and maybe leading edges of the wing, and bottom of the fuselage. I think this has been covered before, and what systems guys are using with specific dope build ups. You can watch the weight better also. Charlie Reeves did this on his Humbler. If I get to build what I want to this winter, I plan to try the DuPont Nason system. It's available in small quantities, supposed to be ready to shoot once it's catalyzed, and I think this is what Charlie used, but not really sure.
Type at you later,
Dan McEntee
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I generally wait about a week to 10 days in a warm shop. It will generally gas off enough over that period. But as Mark said, it's variable. Never had much problem with reactivity so there is that. Only problem comes if you have to repair something, but that's an process.
Keep in mind that while automotive polyurethane clear is much, much more resistant to fuel than lacquer, it's not "fuel proof". Leaving raw fuel on it will blister it just like it will any other paint.
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It does not need to be totally fuel proof. Something more resistant than dope is a big improvement.
It looks like it is time to try Klass Kote on the next project.
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I have PPG 2021 clear on my Avenger, It has in fact had raw fuel bathe it occasionally and have seen no problems at all. Well not entirely true, when Powermaster came back with the GMA fuel and the purple dye, that purple did want to stain my clear on the bottom some but I hear they discontinued that dye..
but as to fuel proof, like i say, I have not seen a problem, not that I would recommend pouring raw fuel on it and leaving it, but its certainly far more stable than dope
another note to consider, the cost of the two part clear you use, ( well technically not the cost but it seems to be relative) the less expensive Urethane clears like Omni consumer grade and lower priced alternatives are a higher percentage of acrylic versus the higher end stuff tends to be a higher percentage of Urethane. The Urethane tends to make it much more chemically resistant than does the acrylic.
However the flip side is that the higher acrylic content clears are generally easier to spray and polish
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OK, my 37 cents worth. I've been using two part auto paint over dope for 11 years. I've gotten away with waiting as little as a half hour for clear coating dope. I got away with it. Repairs for me often happen like that.
I've used PPG Deltron 3000 at the high end and Omni at the low end. Everything I've tried has been fuel resistant. Raw fuel sitting in puddles will remove the finish, even the expensive stuff.
Deltron 3000 or the 2021 is really tough, nearly impossible to sand or remove anomalies once it is completely cured. The cheap stuff like Omni, because of the acrylic content stays easy to sand and repair for the duration on the model's life span.
I've heard, "You can't repair a U coated finish over dope." I say BS! Here again is where the acrylic content comes into play. More acrylic seems easier to repair, assuming the base is dope. The only problem I've had is blending trim, that is removing tape from a trim line. Practice helps a lot and I've had plenty. Use low tack tape and remove it in the direction that takes you from the urethane to the dope, carefully. I've done this in as little as half-an-hour's time also. PPG high end stuff works the same way but take more patience.
I recently refinished my Freedom 45, including cutting into the turtle deck and installing new controls. New control surfaces, new embellishments and blending in all of the trim where the repairs were done. It was good enough for 19 points at the Golden State Champs last fall.
That may have been more than 37 cents, but you get the point.
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I don't think it is really necessary to cover the whole model in the two part stuff. Just do the nose section and maybe leading edges of the wing, and bottom of the fuselage. I think this has been covered before, and what systems guys are using with specific dope build ups. You can watch the weight better also. Charlie Reeves did this on his Humbler. If I get to build what I want to this winter, I plan to try the DuPont Nason system. It's available in small quantities, supposed to be ready to shoot once it's catalyzed, and I think this is what Charlie used, but not really sure.
Type at you later,
Dan McEntee
Dan, I've probably sprayed close to a total of 4 gallons of Nason on custom guitars and stunt ships over the last ten years or so, (don't remember exactly when I started using it), with great results. The only issue I've ever had was on an instrument in the winter that I didn't wait long enough for the outside shop to warm up and the stuff failed to kick properly. We're talking 38 degrees, so I paid for my impatience. I'm not sure when they started producing Nason, but I got onto it very early at my local shop's recommendation.
When you mix, be sure the catylist is sealed really tight, and then I also put the little can in a baggy and seal it up because it can draw moisture and be ruined. Yeah, you can ask me how I know that.
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Dan, I've probably sprayed close to a total of 4 gallons of Nason on custom guitars and stunt ships over the last ten years or so, (don't remember exactly when I started using it), with great results. The only issue I've ever had was on an instrument in the winter that I didn't wait long enough for the outside shop to warm up and the stuff failed to kick properly. We're talking 38 degrees, so I paid for my impatience. I'm not sure when they started producing Nason, but I got onto it very early at my local shop's recommendation.
When you mix, be sure the catylist is sealed really tight, and then I also put the little can in a baggy and seal it up because it can draw moisture and be ruined. Yeah, you can ask me how I know that.
Thats a very good point, I tend to forget that since my source has a fairly consistant turn over on catalyst..
also, use a good spray guy :)
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Good point Will. I've lost 2 cans of catalyst because it wasn't properly sealed. Turns to jelly. Joy.
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I generally wait about a week to 10 days in a warm shop. It will generally gas off enough over that period. But as Mark said, it's variable. Never had much problem with reactivity so there is that. Only problem comes if you have to repair something, but that's an process.
Keep in mind that while automotive polyurethane clear is much, much more resistant to fuel than lacquer, it's not "fuel proof". Leaving raw fuel on it will blister it just like it will any other paint.
Hi Randy,
The Sikkens polyurethane that I have used for years is very resistant to most chemicals. On full-scale airplanes painted with Sikkens polyurethane I have used straight MEK to wipe off exhaust stains on the side of the fuselage such as on the Dreadnought Hawker Sea Fury Reno racer and various P-51s, and on my models it is totally resistant to MEK, straight model fuel at 20%, and model exhaust with no disturbance of the gloss. Sikkens is not cheap but for the results is seems to be worth it, especially as a little bit goes a long way.
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Hi Randy,
The Sikkens polyurethane that I have used for years is very resistant to most chemicals. On full-scale airplanes painted with Sikkens polyurethane I have used straight MEK to wipe off exhaust stains on the side of the fuselage such as on the Dreadnought Hawker Sea Fury Reno racer and various P-51s, and on my models it is totally resistant to MEK, straight model fuel at 20%, and model exhaust with no disturbance of the gloss. Sikkens is not cheap but for the results is seems to be worth it, especially as a little bit goes a long way.
Hi Bill;
What is your opinion of shooting a single coat over the nose of the model back to the wing and out the leading edges about half way? The main areas where one might drip or spill raw fuel. If it lays nice and clear where you don't see a separation, That could save a bit of weight and help with repair difficulties and recovering. What kind of sizes is the Sikkens available in in your area? I'll have to check out the local paint shops.
Type at you later,
Dan McEntee
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Bill, they will all crinkle if raw fuel is left on it. Ask me how I know.
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Hi Bill;
What is your opinion of shooting a single coat over the nose of the model back to the wing and out the leading edges about half way? The main areas where one might drip or spill raw fuel. If it lays nice and clear where you don't see a separation, That could save a bit of weight and help with repair difficulties and recovering. What kind of sizes is the Sikkens available in in your area? I'll have to check out the local paint shops.
Type at you later,
Dan McEntee
I am not Bill, but I have sprayed a bit of clear hear and there
I would not try to spray part of hte airframe with uerthane, so many possible issues arise. not the least of which is getting the edge to lay down. If you were insistand on doing this, I would try to spray the majority of the fuse and make your dry edges in the fillets on the wing and stab, but I really dont know why you would not just clear the airplane completely
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I'm with Mark on that; you won't add enough weight to make a significant difference by spraying the whole ship if you're careful. It looks absolutely wonderful if you do!
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Bill, they will all crinkle if raw fuel is left on it. Ask me how I know.
Randy,
Sikkens does not "crinkle" at all with raw fuel, MEK, Acetone, or any other solvent short of concentrated acid to which I have exposed it. "How I know" is that I have years of experience with this product (since about 1979.)
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Hi Bill;
What is your opinion of shooting a single coat over the nose of the model back to the wing and out the leading edges about half way? The main areas where one might drip or spill raw fuel. If it lays nice and clear where you don't see a separation, That could save a bit of weight and help with repair difficulties and recovering. What kind of sizes is the Sikkens available in in your area? I'll have to check out the local paint shops.
Type at you later,
Dan McEntee
Hi Dan,
I would agree with Mark in that I do not see any reason not to clear the whole airplane. If you do not overload the airplane with clear then the cost/benefit ratio (weight gain/fuel proofing) is well worth it. If you are shooting the poly over dope then there are not very many ways, at least that I know of, to feather the poly edge. If you were shooting poly clear over polyurethane then you could shoot slow urethane reducer lightly on the edge of the fresh clear and mostly blend the edge of the clear, which could then be buffed to an invisible blend.
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Hi.
2 component acrylic clear is really nice and fuel- and whatever chemical-proof, but I would not put it over 1-component paint. Not even the 1-component acrylic colours from same maker and I doubt that dope or such will give better results. The 2 layer system works well with cars, with much thicker layers than we want and also with wet-on-wet application.
All is fine untill you need to repair the paint job, the colour base will wrinkle where clear has been sanded through and sprayed over.
I use only 2-component products from beginning to end. For colours, I use cheap industrial polyurethanes. Especially metallics are really light and at least equally resistant as clear acrylic.
Even like that, I have never been able to fade away a sprayed edge by sanding and buffing, I find it's better to leave a sharp edge over an inkline or something else that hides it. A visible repair is good, it reminds me of my stupidity.
Well, soon I'll find out..
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Jim, for what its worth, Eric Viglione has been using klasskote epoxy paint and has been very happy with it. Personally, I have been using DuPont 480S clear on the last few airplanes with good results.
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480S is just an acrylic lauquer clear isnt it? no catalyst, I cannot imagine it is very fuel proof, most acrylic lauquers are pretty vulnerable to nitro
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Yea, Howard used 480S awhile back. He was obsessively wiping it and had to be very careful about fuel spills. Came right off with nitro. Be OK for electric, I suppose. Just stay away from guys in the pits slinging around fuel. ;D
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I used PPG Duracryl. Nice stuff, but it's getting scarce. It's also soluble in all alcohols and in the low-viscosity oil that was fashionable a few years ago.
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I used PPG Duracryl. Nice stuff, but it's getting scarce. It's also soluble in all alcohols and in the low-viscosity oil that was fashionable a few years ago.
which is sad, Duracryl is fabulous stuff to spray and polish,,
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I still have a quart of DuPont 480S under the bench. I checked it while back and it's still usable. It's like 20 years old but tightly sealed. Go figure.
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My goodness! There are so many kinds of automotive clear! I have been using Dupont "Nason" 496-00 urethane, with the recommend catalyst (4:1 mix). Unfortunately, raw fuel does affect it.
Floyd
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Doesn't raw fuel get to any clear that has not had time to fully cure. The stuff I use from the auto paint store, the guys says to give it two weeks to fully cure.
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Even when fully cured, it will be resistant to raw fuel. More resistant than dope. A lot more. But it's not impervious, just resistant.
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My goodness! There are so many kinds of automotive clear! I have been using Dupont "Nason" 496-00 urethane, with the recommend catalyst (4:1 mix). Unfortunately, raw fuel does affect it.
Floyd
That is baffling. I have used it for several ships, never had an issue with it.
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That is baffling. I have used it for several ships, never had an issue with it.
Will,
Possibly, and I'm guessing, manufacturers recommend not reducing this stuff more than 10%, as I remember, so the issue could be with thinning?
I used that stuff for a good number of years and never had any issues. Experience or not, always read the can or call Tech.
Charles
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Will,
Possibly, and I'm guessing, manufacturers recommend not reducing this stuff more than 10%, as I remember, so the issue could be with thinning?
Charles
short answer NO
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for those who have had solvent ie fule issues with catalyzed clear, two things,
typically less expensive clears have a higher percentage of acrylics ( versus Urethane) as the percentage of acrylic goes up, the chemical resistance goes down.
the upside is, the more acrylic clears are far easier to spray and more significant, easier to polish
another is that we as hobbiest tend to not have a temperature controlled booth to spray in. when spraying two part materials, it is imperative that they be kept over 65 degrees for the first 24 hours ( this is a generalization, some products longer some shorter) If you do NOT do this, the material will not completely cross link ( the catalysation process) and will be more chemicaly sensitive regardless of the product.
the only way solvent will create a less resistant surface is if you use the wrong solvent, as in using lauquer thinner or a reducer that is to fast ( or in extreme cases to slow) for the conditions which traps solvents in the clear. Then the clear catalyzes, and after its hard the microparticles of solvent eventually migrate out and it leaves the material with a level of pourosity it should not have.
The biggest singel reason I am aware of with catalyzed clears ont being chemically resistant like they should be is that we, as stunt guys, want LIGHT and as a result tend to out of fear spray very very thin topcoats. This will not work with these clears, they still need to be a certain mil thickness to maintain their integrity. Think for an example, using Lite silkspan versus heavy silkspan, you can get away with light silkspan until you introduce something ( a pebble or an insensitive finger) which then overcomes the integrity of the thinner material. Whereas the breakpoint of the heavier sillkspan is much higher and more tolerant of intrusions.
Hope this helps with understanding
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mark,
All you say is true (liked you needed me to say that). But my experience has been that catalyzed clear coats are enormously resistant to raw fuel. As I said, much, much more than lacquer. I had a plane that was upside down in a UDP. Unbeknownst to me, it has a fuel tank leak. Fuel leaked out, through a vent and down the outside of the nose. The plane sat that way in the UDP for about a half hour. When I grabbed the plane to turn it over raw fuel had ate it's way through the clear.
Now this is an extreme case. It's the only time I've had fuel do more that slightly and briefly discolor the clear. But it taught me that the stuff, while very good, isn't indestructible. But I will keep using it. Beside, electrons don't do anything to it.
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Mark doesn't need my "yes, that's right", but I'll ad it anyway, especially the temperature thing. As I said in a previous post, strange and unpleasant things happen if the temp isn't where it should be when you spray. My new building will have a dedicated spray booth that is temp controlled, dust free, and a with good exhaust system. It's worth all the "loss" of space in the building!
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for those who have had solvent ie fule issues with catalyzed clear, two things,
typically less expensive clears have a higher percentage of acrylics ( versus Urethane) as the percentage of acrylic goes up, the chemical resistance goes down.
the upside is, the more acrylic clears are far easier to spray and more significant, easier to polish
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Hi Mark,
Another aspect of automotive polyurethanes besides the percentage of acrylics is the ratio of base clear to catalyst. Typically, the less expensive polyurethanes use a high ratio of base clear to catalyst such as the old Du Pont "Imron" at 3:1 base resin to catalyst (a paint that I used to like due to its wide color selection, good gloss, ease of application, pretty good chemical resistance, and ready availability.)
Automotive polyurethanes are available, depending on the brand, in base clear to catalyst ratios from 8 parts base to 1 part catalyst to 1 part base to 1 part catalyst. The higher ratio polyurethanes have less chemical resistance compared to the 1:1 ratio polyurethanes. Bostic-Finch polyurethanes use a 1:1 ratio and are completely resistant to anything short of concentrated hydrofluoric acid and very caustic paint stripper. The difference in ratios is due, as you mentioned, to the amount of acrylic used in the base clear, and along with the higher percentage of acrylic goes less resistance to chemicals. Of course, as the ratio of base paint to catalyst goes toward 1:1 the cost goes up.
Bostic-Finch (and other 1:1 ratio polyurethanes) as applied have a very high gloss but are difficult to polish when fully cured, although there is a brief window of time after application where it can be polished. These polyurethanes are also less flexible than the higher ratio paints.
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PPG Durethane fits that, I think it was a 2:1 mix ( plus reducer) and you could polish it on the day after you sprayed, but not on the third day,, it was brutal to polish, but man it held up to most anything, it was like a cockroach,, anything up to a nuclear blast LOL
for the record, I pretty much disregard any of the ultra hi end clears when discussing here, I dont know many who would want to spend the money, or deal with the ultra hard surface here,,,
for my money, PPG 2021 or 2042 is about as top of the line as you would want to go in our world,, ( and yeah, its not really top of th eline in the grand scheme,, I love Glasurit clears and Sikkens clear is water wet and clear awesomeness,, but it can be spendy)
higher acrylic levels make it easier for the hobbiest,
thanks for the additional info though,, always good to learn more,, I have never heard of Bostic-Finch, maybe the next show car I spray,,,,,,,,
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I really like HOK Kosmic Klear. It's a 2 to 1 with reducer. Crystal clear. and a pain to polish but it sure looks nice when it's done.
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About the original question I'd listen to what Howard Rush has to say about the wait.
John
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I used to both sell and use dope many years ago. LL~ LL~ ~>
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I used to both sell and use dope many years ago. LL~ LL~ ~>
Yea, me too.
I had a bunch of Randolph dope and thinner I sold to another modeler.