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Author Topic: what universal paints go under oil based clear polyurethane for fuel proofing  (Read 391 times)
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azzanz
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« on: August 11, 2018, 06:08:47 AM »

fuel proof hobby paints are hard to get in my country and international shipping is real costly to get them here from UK or USA, ive researched that oil based polyurethane is glow fuel proof, but im not sure what colour i can put under the poly,
i would like to use dupli color as its readily available and is a quality paint ive used it before, but other than doing a test im not sure if the poly will craze the dupli color or vise versa.
or can i use any oil based colour from hardware shop? ie craft type oil based paints?

thanks in advance from new zealand
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Konrad
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« Reply #1 on: August 11, 2018, 12:11:17 PM »

First always make up test coupons. I do this as the formulation of paint products is alway in flux often as a result of regulatory requirements.

Now what do you mean By "Glow Fuel Proof"?

If the paint is impervious to methanol it will work fine with FAI fuel 80/20, most oil based paints are. The problem come when fuels use nitromethane in their formulation. Nitromethane is a strong solvent, much stronger then methanol.

Most oil based polyurethane paints are only "Hot (nitro) Fuel Proof" to 15% nitro. My experience is that the paint shine is often lost with fuels that have a nitromethane content above 5%.

If looking for real fuel proof paints I'd look at the modern catalyzed (two part) automotive polyurethanes. I assume that there are automotive repair suppliers in New Zealand.
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azzanz
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« Reply #2 on: August 11, 2018, 09:18:28 PM »

yes i can buy 2 pack paints  but no way can i afford them and all the safety gear and equipment  needed to paint them.
i can buy a few colours of rc  aircraft paint in spray form but colours are very limited.
ill do like you say and use test cards for the polyurethane i will be using 15% + nitro  but would it still be an issue in the exhaust oil? sprayed on the plane, i could understand if i was spilling raw fuel all over my it  all the time but generally that doesn't happen.
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Konrad
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« Reply #3 on: August 12, 2018, 12:16:09 AM »

yes i can buy 2 pack paints  but no way can i afford them and all the safety gear and equipment  needed to paint them.
i can buy a few colours of rc  aircraft paint in spray form but colours are very limited.
ill do like you say and use test cards for the polyurethane i will be using 15% + nitro  but would it still be an issue in the exhaust oil? sprayed on the plane, i could understand if i was spilling raw fuel all over my it  all the time but generally that doesn't happen.
"Hot" is american slang for powerful. You are correct in thinking that the issue is not the oil after combustion but rather the raw unburnt fuel.

The use of the old 2 part polyurethanes is to be avoided (AKA Imron). Most modern 2 part automotive polyurethanes are water based. True all aerosolized paints are dangerous and need proper protective equipment.

To the best on my knowledge 15% + nitro need catalyzed paint, epoxy or urethanes!
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azzanz
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« Reply #4 on: August 12, 2018, 04:59:10 AM »

for this model i think i'll use pactra formula-u while i can still get it and a local shop has it on special less than half normal price,and i'll experiment with hardware shop  polyurethanes at a later date.
i've got no issues using spray cans at home in well ventalated spot but i wont be using hundreds of dollars worth of epoxy car paint on a $35 plane model unfortunatly.
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Konrad
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« Reply #5 on: August 12, 2018, 11:47:43 AM »

Formula-U never worked well for me. It was heavy and not very "Hot Fuel Proof" 10% nitro was about the max it could withstand and then you had to be fast with the clean up. 15% or more nitro fuels were out of the question. I also recall an adhesion problem. I think I tried Formula-U over both nitrate and butyrate dope bases.

Horrible stuff!
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azzanz
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« Reply #6 on: August 12, 2018, 12:32:57 PM »

maybe thats why the shop has it real cheap... no one buys it
might give it a miss in that case
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Konrad
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« Reply #7 on: August 12, 2018, 12:51:21 PM »

That would be wise.

Nitromethane is a problematic substance. I found that I really did need it when running well designed and tuned engines. I only used it if the contest event required it. Scat Cat racing (Q500) needed 15% or AMA F-1 where we used 65% nitro.

For sport flying of 2 cycle engines, FAI 80/20 really is the best as it allows for a wide selection of model finishes.

Most european engines run well on zero nitro and most other quality brands can be made to run well with simple modification to the engine. 


All the best,
Konrad
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Konrad
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« Reply #8 on: August 12, 2018, 04:19:47 PM »

That would be wise.

Nitromethane is a problematic substance. I found that I really did DIDN'T need it when running well designed and tuned engines. I only used it if the contest event required it. Scat Cat racing (Q500) needed 15% or AMA F-1 where we used 65% nitro.

For sport flying of 2 cycle engines, FAI 80/20 really is the best as it allows for a wide selection of model finishes.

Most european engines run well on zero nitro and most other quality brands can be made to run well with simple modification to the engine. 


All the best,
Konrad
Sorry logic problem mistyped It should have read:
Nitromethane is a problematic substance. I found that I really DIDN'T need it when running well designed and tuned engines.
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