Acrylic or Polyurethane paint? Etc...

[peterh337]

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 (http://www.hex.co.uk/tds/upol/acid8.pdf)) 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 (http://mapaero.com/galeries/fiches_techniques/gb/100.pdf) "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 (http://www.deluxematerials.co.uk/pages/aeroproducts.htm)) 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.

[Fuji Abound]

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.

[peterh337]

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.

[werewolf]

Mapaero : The company > Presentation > MAPAERO - AEROSPACE COATINGS > 09100 PAMIERS > 09 - Arige (http://mapaero.com/?idMenu=75)
Minimum order : 5kg. From 1 to 5kg: extra charge euro 60.

[goldeneaglepilot]

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?

[peterh337]

The respirator I use is the 4277 (http://www.protecdirect.co.uk/Half-Masks-and-Full-Masks/3M-Vapour-and-Particulate-Respirator-%284277%29.htm) or (got some coming) the 4279 (http://www.arco.co.uk/products/116900). 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.

[Shoestring Flyer]

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.

[Crash one]

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.

[Shoestring Flyer]

The answer....take up the fags!!....no-one has ever died from smoking have they???:D

[goldeneaglepilot]

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...

[Crash one]

Obviously shouldn't have mentioned the fags.:ugh:
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.

[peterh337]

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 (http://www.spraygunsdirect.co.uk/product.php?tid=100&products_id=5811) looks a lot better though, with the A2 (activated carbon) filters for organic solvents.

[goldeneaglepilot]

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.

[A and C]

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!

[Crash one]

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,
"Aeroplanespecialexpensivecanonlybeappliedbyexpertsatvastcost" 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.

[goldeneaglepilot]

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.

[A and C]

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.

[mr_rodge]

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!

[cockney steve]

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.

[Croqueteer]

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.

[cockney steve]

@ Croqueteer. Domestic oil-paint is the worst of all worlds for painting an aircraft.....If you want an air-drying (as opposed to chemically curing) paint, use Transport polyurethane, AKA "Coach-enamel" warm it to thin it , spray or brush...super gloss, lower shrinkage than dulux, quicker tacking to "dust-dry" quicker hardening , tougher and less shrinkage. any automotive paint supplier will be able to colour-match exactly as well as supplying the correct thinner, primer etc. to give you the best-protecting, most durable finish.

I have ,myself , sprayed domestic radiators with thinned, warm Dulux...excellent finish but a bugger to handle until hardened.

much better to paint the inaccessible portion only, then fit and commission.....spray/roller/brush the acessible bits when it's cooling down....too hot and it will have a dull surface spoiled by "solvent-pop" or a brush will tend to stick.....get it warm enough and all brushmarks will flow out, leave for a couple of hours and then turn up the heat and it will bake itself :)

[mr_rodge]

cockney_steve,

Thanks for the in-depth reply. I'm using a 2-pack paint with Valspar UD-429 instead of the hardener (same 2:1, but with about 30% thinner), which allows the paint to air dry. It apparently won't kill me, but the smell certainly gives the impression it will so I still wear a respirator & goggles, just in case. From what the guy in shop said it's similar to the stuff they use to make aerosol paints dry. It supposedly sets just as hard, but takes much longer to cure.

Visited a shop yesterday and they gave me some acrylic paint to mix with the Valspar, hopefully it'll work just as well as the last bit I had.

My next conundrum is the spraying... I thought I'd done it pretty well until I saw the orange peel at a certain angle, and I wondered why the 30% gloss paint looked high gloss.

The guy in the shop said I'd probably had the gun too close to the panel and that's why it dried glossy, he said to spray it on 'dry' and it'll have the intended finish. I'm using RAL 9010.

I'm now wondering if it's the cold air causing the orange peel or my crappy gun, if it's the latter can you recommend a compressor/gun rig? If it costs me £250 it'll still be cheaper than me replacing 20-odd cabinet doors. I always keep the paint and panels I'm practicing on in the house and only take them to the cold garage to spray, as soon as they're dry enough to handle they come back in the house.

Thanks again.

[cockney steve]

I'm not familiar with the Valspar, in fact the whole refinishing trade has changed dramatically since the limitations on voc emissions.

However, a broad generalisation or two.

do not mix different manufacturer's products and systems.

just because a 2-pack product will air-dry, doesn't mean it will have the same characteristics as the proper, catalysed chemically-cured mix.

A "dry" coat willtend to show more orange-peel also the film density and strength are questionable.

30% is a LOT of thinner! note the "speed" of a thinner has a huge effect on the finish...you really need to understand the science behind spraying ...there are many textbooks and some manufacturers used to do excellent tech. sheets. / maybe still do.

Viscocity of the medium is affected by temp and solvent-content....you then need a correct air-pressure and volume to atomise to right droplet-size (uniform,with minimal fog or heavy particles) then the thinner-formulation.....once the fluid is atomised, the "fast"portion evaporates between nozzle and work...thus the droplet consolidates...it should contain enough solvent, that it flattens and dissolves into it's neighbouring droplets without splashing a fog everywhere (dulls the finish and alters metallic colours)...too little that flashes -off too quickly, means the droplet won't fully flatten and merge = "orange-peel! "

So, no matter how warm the paint and the work, if the ambient is yoo cold, your finish will be affected.

Another little-understood facet ,=the air-supply!
a compressor and airline act like a primitive fridge!!!!

air is compressed and so is the heat it contains so your compressor gets hot and the moisture condenses out (important to drain the tank regularly and use an oil/water separator on the output)

the tank full of compressed-air will stabilise at ambient but, of course, contain less heat ( think kettle of boiling water V egg cup full....both contain boiling water, the kettle holds a lot more heat )

When you pass it through the spray-gun, it expands...suddenly , the heat in 1 cubic of compressed air,is now dispersed into , say 5 cubc feet of free-air...so the temperature drops your paint-droplets congeal, but don't flash-off the solvents the same as when they're warm,,,also the temp-drop can condense ambient moisture into the paint and onto the painted surface......

I'm only scratching the surface of the subject, but observe the basics...clean, dry and warm, thin, properly "wet" coats (although there are exceptions - some etch-primers are specifically dusted in a dryish translucent film) correct viscocity and correct volume and pressure at the gun.....airline has a known pressure-drop depending on diameter and length, so 60 psi at the regulator ,could well be only 35 at the gun!

Many old-school painters knew nothing about the forgoing, it was all empirical knowledge, passed-down through apprenticeship and experience,-what worked, what didn't and the little dodges....paint too thick? reduce flow-rate /move gun closer to the work, and so-on.

hth. steve

good results can be obtained with very modest gear....many young mechanics are conned into a chestful of snap-on spanners at £20 a go and many painters are convinced that ONLY a£200 De Vilbiss gun will paint properly......in both cases, it's a mix of brain and brawn....think objectively and apply to your hands...you can't buy skill but you can readily learn it!