Question on two-pack paint
 

My TB20GT is painted with MAPAERO paint.

Socata, like most French firms, like to buy stuff from French suppliers even if it costs 5x as much, and this paint is hard to get. One can get it, but the minimum is 1 litre packs which is way too much for touch-up jobs, given that one needs to buy half a dozen packs to get the full prescribed set (base colour(s), thinner, hardener, diamond pearl topcoat).

Q1: Is Mapaero any better than the paints which normal GA paint shops use?

Q2: Is the "hardener" actually necessary? I have the complete set of the other paints at present (having scrounged various little bits from Air Touring before they went bust, and having got some leftover from a bigger paint job) but have no hardener left. The stuff seems to dry perfectly well without it. I know that with epoxy paints the hardener is obviously absolutely required but this is not epoxy paint.

For primer I use the standard aviation zinc chromate primer. I wonder however if etch primer (as used in the car trade) is better for steel or bronze parts.

I dont know the answer but I have not come across two pack paint that doesnt have an epoxy component so I would also be interested to now the purpose of the hardner. You would assume the fact that it is in two parts would suggest some form of chemical reaction takes place after mixing which you wouldnt want going on in the tin (were it premixed).

This is the stuff.

2 pack paint will dry out but not cure without the hardener. It won't weather properly or protect like that. It's 2 pack for a reason!

I concure with bose. The stuff is useless if it doesn't cure.

You can get some types of protective paint which cure with oxgyen exposure.

All that happens if you let it dry is that the suspension medium evaporates and you have the unactivated ingredient just sitting on the surface. It will be permiable and as such won't stop O2 and other undisirable chemicals near the metal.

I'd be hoping to get some input from people who actually know about paint chemistry...

The fact is that the paint seems perfectly fine, after ~10 years, when applied onto small areas without the hardener.

It is apparently just as good as the original Socata paint, which while generally very well done has been known to peel off rather easily in large strips, leaving behind just the green primer. This happens around the filler caps, where careless refuellers tend to chip it. One assumes that they sometimes applied it under conditions of temperature or humidity which were outside the painting spec.

There is two types of knowledge on paint to be honest.

I have the engineers knowledge off process and what codes to go for and depth etc.

And then you have what your looking for which is the industrial chemist production. Which is a very rare beast indeed.

In alot of cases the paint is more cosmetic than actually doing anything. In these cases it doesn't really matter what you do it will always work out. But then when it is actually there for a purpose it is very important to do it exactly as it says on the tin.

By not curing it you won't have bonded all the molecules together it will be sitting there a bit like compacted and dried sand. It will be able to support some loads and shear forces but won't be accept the load that it would if you had put some cement through it.

An example off the top of my head would be if you had fixed a patch on your roof and a seagull shat on it and you left it for a month. I would expect that the uncured patch would allow the acid to get to the metal underneith and destroy the paint, where as the cured patch you could wash it and you would have never known it was there.

BTW if you need more hardener if you get your hands on the COSH sheet for the hardener you can find out what catalyst they are using. From memory there are 3 types for polyurethane catalyst depending what enviroment you want it to cure in. Then you can just order a bottle of it.

I presume you have had a read of this?

Polyurethane - Wikipedia, the free encyclopedia

From my experience with automotive paint, it's very embarrassing if you don't put enough hardener in when spraying 2k paint. Not putting any in will leave you with a nice sticky mess to clean up, which is a total pig of a job to do :ugh:

As with the last poster, my experience is with Automotive 2-pack.

I have to add that an aquaintance, with the cooperation of a qualified Engineer, stripped and repainted his 172 at his own body-shop, using Sikkens automotive paint (Autocryl)

the hardener is of paramount importance and a graduated mixing-stick,together with a parallel-sided,flat-bottomed,small-radius-cornered container ,are also crucial to accurate mixing-ratios,in the absence of digital-scales and fresh, correctly-stored materials.
Mixed and applied correctly this paint-system is extremely tough,glossy and resistant to UV, chemicals and weather.....it is little short of indestructible.

The downside is that the resin carrier and catalyst are isocyanate-based and breathing-apparatus is a must. breathing the cyanide fumes quickly leads to all sorts of respiratory problems.

yes, the paint will DRY....but without the catalyst, it won't cure and will have a durability approximating Dulux.
OK, you CAN touch-in the odd chip,with just the paint, but it's not hard to count the appropriate number of drops from the mixing-stick (3paint, 2 hardner,1 thinner, IIRC) stir together with a lolly-stick or screwdriver, dob-on with a cocktail-stick, cure with a hairdryer in 5 minutes :8

This stuff is like liquid Araldite. Air-drying paints work by reaction with the Oxygen in the air (oil-based /coachpaint) ,or evaporation of the solvent (cellulose) I would not go back to either for auto/marine/aviation


You MUST clean equipment immediately and thoroughly after use,- a half-full spraygun will contain a block of jelly after about 3 hours at normal room-temperature......at 12 hours it's probably "potted" solid.....same with brushes,mixing-sticks etc.

And conversely putting too much in will make it bubble up, as I found out:\

Peter, suggest you give Safinah a call. They are Marine Paint technology experts but I would imagine the technology is similar.

Cellulose?

SGC

SGC,

Cellulose is a single-part product based on cellulose (surprise, surprise) derived from vegetable matter. I'm sure with your aviation knowledge you know that.

In aviation circles it is used in dopes and in automotive circles it was used in car paints (but the latter have switched to water-based acrylics).

To others, particularly Peter337:

If the paint is a true 2-pack (i.e. with a paint and a catalyst [hardener]) then once it is cured it can be overcoated with anything if it is is keyed (sanded or de-nibbed) properly.

Etch prime is not 2-pack (it doesn't catalyse), it is 2-part (i.e. 2 parts that do not chemically combine), so beware using it if you need a solid substrate to a top coat.

Further 1, if your zinc chromate primer comes in spray cans, it is for the large part completely useless, since the decent properties it used to hold were banned by treaty years ago. Get a spray gun and use 2-part etch prime.

Further 2: Etch prime is hygroscopic. It absorbs moisture, so do not use it on steel or aluminium without overcoating it. It must be covered within 16 hours with a primer (or top coat). If in excess of 16 hours, then it must be keyed with 600 grit (or de-nibbed with Scotchbrite), or alternatively a quick flash coat of fresh etch prime before immediately coating with your chosen primer.

I always overcoat etch prime with a 2-pack epoxy glazing primer, but 2-pack acrylic primer would do.

If you intend using a 2-pack finish coat (gloss coat), then a single-pack acrylic primer will do, as it means you don't have to sand it down) then apply your modern automotive gloss coat colour-matched to your existing paint scheme.

Sorry if this is long-winded.

Russ

Not at all long-winded - very useful :ok:

I have noticed that the standard aerosol zinc chromate primer is pretty rubbish. It has poor adhesion and even the aerosol spray is uneven. I have tended to use 2 or 3 coats to get coverage.

But then I do only small items.

I will probably try to get hold of the Mapaero hardener... On the bottle (I have an empty one) it says
1,3,5-TRI(6-ISOCANATOHEXY-2-PROPYLE,XYLENE
(literally, including the missing closing bracket)
which picks up a few hits in google...

On a related topic, can acrylic 2-pack paint be used on aircraft (i.e. is it avgas splash resistant, etc) and if so can it be applied on top of polyurethane paint?

I have a car paint shop about 1 minute's walk away which does clear lacquer every day, and would be dead handy for small components, but they use acrylic.

A couple of years ago I touched up a few spots with an aerosol from Halfords :) and without exception all the areas showed massive shrinkage (cracking) of the paint. Underneath was the standard zinc chromate primer. But the cracking did not start for about a year. What would cause this? Could it be low temperature exposure e.g. -30C? Those areas have since been resprayed with the 2-pack Mapaero paint anyway.

Try talking to Jawel Paints in Stirchley, Birmingham. What they don't know about modern paints, both single part and two part is not worth knowing. They do excellent colour matching (Send them a sample of the colour painted onto the inside of a slice of a coke can), will advise on techniques and methods and will sell small quantities for touch up.

Paints changed dramatically some years ago in the UK due to the problems with CFC's, health (Isocyanate) and European legislation.

Most car body shops low heat bake the work, if your doing touch up on your aircraft then its best with a two pack paint Isocyanate based paint with the correct hardner for air cure temperatures. It will not be touched by oil, fuel etc.

Yes, in fact they sell 2-pack aerosols on Ebay. They don't say what they are, and I assume they are acrylic like most car paints are these days.

I wonder what the shelf life of a pre-catalysed 2-pack aerosol is?

With all paints they have to have the safety sheets available and it will tell you what they are.

It won't be pre catalysed but it may have something which releases the catalyst when it gets exposed to air.

To be honest all these hardners and paints arn't given the respect that they are due. You can get some extremely nasty exothermic reactions going on if a mish mash of products are all dumped in a box then left to fester and leak.

You can get temprature limits as well if say you use it below 10deg the catalyst doesn't activate. The medium evaporates before the chemistry happens.

The cracking thing is again because of temprature and metal its applied to. Each paint has a range of elastisity if you put it on at say 5degs it can cope with +25 degs above that and -50 below. So you put it on at 5 and the temp gets above 30 it will crack. If you put it on at 15degs you can go to 40 before it cracks.

The engineering codes for protective coverings are full of temprature limits and the like.

I would not worry about the shelf life of pre-catalysed 2-pack aerosol. When its used its vastly inferior to a decent two pack system. I tried some from Jawel which they preload into cans after matching the colour. (How many shades of white do you think there are?) They do warn you its not as good as a proper paint system.

Why not invest a little money in a portable compressor, an airbrush and some decent paint? Its not too expensive and its there for use for the rest of your life.

Very true. I mixed a small amount of WEST epoxy only the other day to join some teak boards - it was only around a quarter of a jam jar and I was very careful to use the correct ration - I had however forgotten that fast epoxy in even small volumes can produce a violent thermic reaction - the pot had to be dumped very quickly as it frothed, gave out copious amounts of noxious smoke and became very hot! It is not cheap stuff so was a sorry waste of a pot of good epoxy - oh well.

(Sorry for the slight thread drift).

BTW having used a range of paints for cars, boats and wood (and even a little on aircraft although I have always managed to avoid them pretty much so far) I still think there is no substitute for two pack epoxy type paints they are so hard wearing, produce an amazing finish (albeit with a little work) and seem to last forever (although a stable base is vital).