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Old 9th Mar 2012, 10:31   #1 (permalink)
 
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Acrylic or Polyurethane paint? Etc...

Poly seems to have been used more or less exclusively in GA during original manufacture, but as far as present-day usage goes, it seems to be going out of fashion and everybody is going acrylic. The "2K" 2-pack stuff is very popular and works very well.

I am told by one supplier (Jawel) that acrylic is as good on avgas resistance as poly. But anyway I can use Aerokote lacquer on top afterwards (on small components).

What do the good GA aero spray shops use?

I am not spraying a whole plane Just little bits here and there.

Another thing is which primer to use. It's patently obvious that the commonly available aerosol zinc chromate primer (from aviation suppliers) is rubbish. It barely sticks to anything, doesn't dry properly, and while it does have the desirable electrolytic protection property which is why it has been used since ~WW2, the rest of the world seems to have gone to 2-pack primers. Or epoxy primers which are obviously 2-pack. They also use etch primer (Acid #8) especially on aluminium or anything galvanised.

Socata used Mapaero poly coatings, which are nothing special apart from being French and sometimes very expensive. Even on the $3M TBM700 there have been cases of large areas just peeling straight off (wings having to be re-sprayed) presumably because the paint was done in too-high ambient or whatever. The problem with the Mapaero stuff is that it is French and is a bastard to purchase from a "difficult" company. Also the shipping is "hazmat" and I have just been quoted 170 euros for shipping on a little 1 litre bottle. The bottle itself is just 30 euros. One Mapaero job I know of took 6 months just to buy the paint... I could almost fly to Tarbes in France and back for 170 euros, but Socata don't sell direct (unless you live in Australia ).

Another Q which somebody may help on is metallic lacquer. In the auto trade this seems to be rather 1970s and not common. For example Jawel won't even discuss it. I have some of the correct Mapaero "pearlescent" metallic lacquer but (as I wrote earlier) I cannot at all easily buy the stupid hardener for it. It is easy to get lacquer (e.g. 2-pack Aerokote) but can one put metal flakes into it? I am not talking about the massive Starsky & Hutch era flakes Just a very fine metal powder.
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Old 9th Mar 2012, 14:35   #2 (permalink)
 
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Peterh337 - said kindly but sometimes the time comes when you are far better off having the whole thing redone. I spent a few happy years "touching up" one particular aircraft and when it was finally resprayed (professionally) wish I had had it done a few years earlier. Moreover I think a patchwork of areas "touched up" complicates a complete respray requiring more preparatory work if a really good finish is to be achieved. Just a thought but the point comes when this may make more sense.
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Old 9th Mar 2012, 15:05   #3 (permalink)
 
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It's not the main airframe. I've had some bits re-done "properly" already. But 99% of it is fine.

I am talking about small parts which get removed during the Annual, get dented etc, and that's a good time to sort them out.

They could be done with any old aerosol from Halfords but I'd like to do a decent job

Actually today I have finished off a couple of little bits, 2K primer, 2K Ford Diamond White base (ever so close to the Socata base colour), 2K clear lacquer. Great stuff and very easy to use.
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Old 9th Mar 2012, 16:01   #4 (permalink)
 
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Mapaero : The company > Presentation > MAPAERO - AEROSPACE COATINGS > 09100 PAMIERS > 09 - Arige
Minimum order : 5kg. From 1 to 5kg: extra charge euro 60.
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Old 10th Mar 2012, 07:05   #5 (permalink)

 
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I agree about 2k paint - easy to use, no more difficult to spray to a good finish than cellulose. The only think to watch is that you specify to the supplier "Air dry" for the hardner as they seem to supply by default hardner for a low bake oven system.

With regards metal finish (flakes) thats a nightmare to both spray and match. Its much more than the mix, its down to individual technique when you apply it for the finish match.

The only caution with 2k is that you MUST use either a good carbon filter mask ( and replace the cartridges periodically) or an air fed hood type mask. The spray mist will not kill you in small quantities (straight away) but will give you some serious health problems long term if not treated with great respect and caution. COPD is an awful way to die.

Good to see that you have a decent colour match Peter, there are an incredible number of variants on white. It surprised me when I first took a white object into Jawel and asked them to match the paint and they produced literally dozens of colour swatches to try to match the colour. They did do a fantastic job of the colour match.

I agree about the etch primers - just be careful to read the instructions about maximum times that they can be exposed to air after initial spraying before applying a primer. Leave them too long and the finish still looks OK but the paint starts to flake off months later.

How are you getting on with your new spray gun Peter? Did you get some gun wash and are you finding it easier to glean up the kit afterwards?
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Old 10th Mar 2012, 08:16   #6 (permalink)
 
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The respirator I use is the 4277 or (got some coming) the 4279. However I am not using a spray booth; I do it next to a wide open outside door.

The spray gun is work in progress Got the gun; just got the pressure gauge for it before I use it properly. Currently still using the airbrush. The gun is certainly a lot easier to clean than an airbrush.

The funny thing about 2K paints is that everybody and their dog is making them. For example the hardener for the primer and base is made in Egypt and is a completely different brand.

I am unable to find the website link posted by werewolf, on the mapaero website. Maybe Mapaero do ship direct to the UK for 60 euros, but I don't want to buy 5kg. Actually I would be amazed if anybody shipped HAZMAT 5kg by courier from France to the UK for 60 euros...

For the small parts, an exact colour match is not important because it is apparent that the small Socata parts (e.g. landing gear door linkages) were sprayed in straight white.

Regards the metallic lacquer, the metal content is very very thin and one needs to apply several coats to be able to see it, and yes I am stirring it very adequately. So, it is not hard to get the desired effect. I just haven't got the hardener so I am not using it.
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Old 10th Mar 2012, 10:24   #7 (permalink)
 
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Please do not spray 2k without an airfed mask. Trust me it will get you!
You may think that spraying a little bit with an open door and a mickey mouse 20 mask will be fine....long term it won't.
It may take 20years but it will catch up with you as sure as eggs is eggs.

Far better to take to a professional plane or car painter who uses proper equipment and not take the risk.
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Old 10th Mar 2012, 10:52   #8 (permalink)
 
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My a/c is LAA permit & I used acrylic 2pk at first for just such small touch up jobs. It all went solid after a few months of storage. I now have a tin of colour matched Polyurethane which I can thin with standard cellulose thinner.
The primer I use is Acid 8 etching primer, also thinned with cellulose. All available at automotive paint suppliers.
I have sprayed cellulose since I was 25, I'm now 72 with no ill effects & I smoke like a train, Still passing medicals.
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Old 10th Mar 2012, 11:13   #9 (permalink)
 
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The answer....take up the fags!!....no-one has ever died from smoking have they???
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Old 10th Mar 2012, 12:34   #10 (permalink)

 
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I think its fair to say that the body's tolerance of cellulose spray and its solvents is different to Isocyanate's.

There are also people who have died of lung cancer at an early age due to smoking, also life long smokers who have lived to old age. But not many people who have lived after exposure to Isocyonates without protective measures.

COPD is the most common after effect in the long term. That is a horrible end...
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Old 10th Mar 2012, 13:21   #11 (permalink)
 
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Obviously shouldn't have mentioned the fags.
The point I was trying to make was that cellulose is safer than 2pack cynanide based pizen. & it isn't really neccessary to spend a fortune on some fancy aviation oriented expensive spray painting outfit to touch up a couple of inspecton panels.
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Old 10th Mar 2012, 15:09   #12 (permalink)
 
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That is my feeling too.

Morally, it is hard to over-do warnings, but...

Look at how much car spraying goes on, every day, all year, mostly with non external air supply masks, in enclosed booths where the stuff builds up to a thick cloud, most of the people doing it are not PhD grade, and they must be getting occassional/accidental sniffs here and there, yet they are not dropping like flies.

This looks a lot better though, with the A2 (activated carbon) filters for organic solvents.
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Old 11th Mar 2012, 10:58   #13 (permalink)

 
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I had an interesting lesson in chemistry last night from an industrial chemist. His thoughts are that both Acrylic and polyurathane two part paints will be isocyanate based (long explanation why). He did say that there are many technical reasons why the modern acrylic two part paints are vastly superior to polyurathane, he did explain why - Long molecules is one thing I can remember (after wine thats difficult...).

He did say though that BOTH are incredibly dangerous to health long term and needed great care and caution.
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Old 11th Mar 2012, 11:34   #14 (permalink)
 
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I think that you need to talk to Mick Allan about this, he has forgotten more about aircraft paint than most of ever have known about it!
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Old 11th Mar 2012, 11:52   #15 (permalink)
 
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The paint I got from an automotive paint supplier is one pack polyurethane not the two pk variety. It is thinned with standard cellulose thinner, it does not require a hardener.
Now, it will probably be pointed out to me that this stuff is not "real" polyurethane & shouldn't be used on an aeroplane. However It produces a perfectly good surface finish, it takes a lot longer to dry than cellulose so keep the flies off, it does not wash off with avgas, whether that means it is fuel proof who knows.
I am not a chemist & know not a lot about this. Today is Sunday, tomorrow I shall go & ask the supplier of this paint what horrific consequences are going to befall me both short term & long term if I live to be 150. At the moment I am quite happy to squirt this stuff around my workshop at small inspection panels, aileron pushrod covers, tailplane brackets etc,without wearing any mask. If I intended to spray a complete aircraft or car I would use a particle mask & ventilate the place.
Isocyanate based systems are a different can of worms. They may well be vastly superior to anything else. Aircraft have been painted without using them for decades without falling out of the sky as a result.
Using something that is not labelled,
"Aeroplanespecialexpensivecanonlybeappliedbyexpertsatvastcos t" is not going to cause the a/c to crash, at a full respray time it will all be removed to bare metal.
Why make a song & dance about it?
Short version. Dont use isocyanate based paint.
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Old 11th Mar 2012, 12:02   #16 (permalink)

 
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Thanks AandC,

The industrial chemist I chatted to has spent a working lifetime formulating paint and ink, my gut feeling is that he was speaking from a technically sound viewpoint. He did explain a very technical argument as to why 2 pack acrylic was better than 2 pack polyurathane - unless your spraying a very large lorry!! The toughness and flexibility of 2 pack acrylic was just one of the reasons he mentioned.

My understanding is that single pack polyurathane is a lot softer than 2 pack when cured.

If you want to be a purist there are still some places where you can get cellulose paints.

The point being made was both are a danger to health.
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Old 11th Mar 2012, 15:11   #17 (permalink)
 
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The flexibility of Two pack paints can be increased by using a plasticizer, as you might expect you use quite a lot of this if you if you Paint a fabric covered wing and a bit less for the plywood structure.

I would think that with the way metal aircraft flex in some parts of the structure a little plasticizer would help but I am not an expert on painting metal aircraft......I leave that to Mick Allan.
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Old 19th Nov 2013, 11:21   #18 (permalink)
 
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Apologies for resurrecting an old thread and this unfortunately has nothing to do with GA but as luck would have it a bit of Googling brought me here...

I'm looking at spraying up my kitchen cabinets (Good, nearly new hard wood that were unfortunately defaced by a terrible toddler living in my house before I bought it, it would be a shame to get rid of it when I may be able to extend its life by a couple of years)

I have honed my spraying skills to an acceptable standard using a cheap HVLP electric sprayer and some Valspar UD429 2-pack to 1-pack converter (safe alternative to isocyanate!). I've gotten good results but now I'm looking to buy my paint from elsewhere. The place I got the paint from describe the 2-pack to be paired with the hardener as acrylic, the shop I'm now looking at just says '2k'.

Is more or less all 2-pack paint acrylic now? Is it the industry lingo standard to get acrylic when you ask for 2-pack, or will some places give urethane?

Thanks!
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Old 19th Nov 2013, 13:21   #19 (permalink)
 
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AIUI "acrylic"|= water-based! A long time ago, there was a choice of cellulose or "enamel" -which was cellulose -compatible for repairs,(Motor-trade) Then in the 60's -IIRC, Vauxhall introduced Acrylic, which was purportedly tougher and shinier and longer-lasting...unfortunately it was incompatible with any cellulose-based primers/fillers/thinners....used to "pickle"-lift and wrinkle, absorb the acetone from celly thinner and swell, so even if you dusted a dryish coat of primer-filler, the subsequent shrinkage would give a sunken edge round the repair (mapping)

AFAIK, ALL 2-pack products are isocyanate -cured, apart from the various primers which are activated by Phosphoric acid (excellent for steel) 2-pack is effectively like spraying coloured Araldite(epoxy resin)

Extremely tough, chemical resistant and durable....resists brake-fluid and battery-acid.

As noted, the down-side is a pot-life of about 4 hours, once mixed, a long Open-time (sticky) after spraying and hard work to polish-outdust and imperfections afterwards.

After about 3 hours dcuring at normal room temp, you can throw newly refinished stuff out into the rain with no ill-effect....try that with one-pack!

All equipment must be scrupulously cleaned and washed through....once the stuff has hardened, no normal solvents will remove it...not acetone (gunwash) nor Nitromors (Methylene Chloride)....bad news forgetting a 200 spraygun and finding a block of jelly in it.

One-pack paints dry, as opposed to curing....they mostly react with the oxygen in the air and the curing is a one-way process...unlike cellulose, where the solvent evaporates, but the paint will afterwards re-dissolve into the solvent.

One-pack polyurethane is extremely durable (anyone remember "Kingston Diamond? ") it's best heated to thin it , a padded,insulating jacket around the spraygun-pot is worth making) The warm paint atomises and flows well and the heat flashes off the more volatile parts of the solvent, stiffening the film and lessening the chance of runs or curtains.

For kitchen units, i'd be tempted to use a 2-pack automotive paint for durability, quick through-hardening and an infinite colour-match capability....provided you use a recognised colour (RAL, Pantone, are standard ranges, or there are millions of car-manufacturer's shades and fleet-shades) you can always get a half-litre of celly or an aerosol made for touch-ups.

With a bit of planning, good results can be obtained with 1-pack Polyurethane (Transport-enamel) and any leftover can be used to touch -up.

Do not even think about ordinary house-paint! Although you CAN spray with good results, I'm less than impressed with the low-VOC water-based stuff. (it's water-base in the motor-trade now,and from what I understand, it relies on the clear-lacquer overcoat for strength and durability.
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Old 19th Nov 2013, 16:54   #20 (permalink)
 
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Painted my cowling recently with Dulux gloss (Oil based) with a small amount of turps substitute, as it was easier to get a match. It sprayed on beautifully and I was really impressed with the finish. I've recovered and painted four a/c in past years and I would consider using Dulux again for the whole a/c. Disadvantage is the longer drying time.
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