How to tell if I got bad paint? Or thinner?

stona said:

Each to their own, but I switched to acrylics for a couple of years before reverting to enamels. My own experience is that enamels are far less likely to cause problems in the airbrush, brush paint much better than most acrylics and are much more tolerant of my approximate thinning technique.

I have the advantage of space at the back of my house where neither I nor any smells interfere with anyone else and a terrific spray booth/extractor which shifts 335 litres of air a minute to the outside. I appreciate that not everyone can be so fortunate and that the smells which are associated with enamel paints can be a problem.

I'll be using them until they ban them! I expect some overpaid and underworked eurocrat is working on that as I type

Many, many acrylic users tell me that the safest way to thin acrylic paints is with their branded thinners. You definitely don't need to do this with the enamels that I use.

Of course there is another possibility, that I'm just an old fart who can't or won't learn new tricks!

Cheers

Steve

Click to expand...

In that case, we'd better form an 'Old Fart's Club' Steve!
I'm exactly the same. Apart from the (now known and recognised) few problems with Humbrol enamels over the last couple of years, I very rarely have a problem with the airbrush, unlike acrylics. Using acrylics always leads to more cleaning, as the paint clogs the 'brush.
I know a lot of very experienced, and very good modellers swear by them, but to me, they're still 'Micky Mouse', and there's no way I'll be convinced that they have the versatility of enamel or other solvent-based paints, particularly for brush painting. The only time I'd ever even dream of using acrylic paints with a paint brush, is to paint a picture, and then only if I was forced to!
As for smell and fumes, I've probably become accustomed to it, after more than 50 years using enamels, but I have noticed when, on the rare occasion I've used acrylic paints in the airbrush, I can feel the effects in my nose and throat, as if there's a coating of 'plasticiser' clogging my nose!
Oh, and bye the way Steve - check your maths! At 50p per liter, 4 liters would be £4 !! But the cost is about right - I recently b ought a 2 liter container from 'B&Q' at a touch over £3, so about £7 for 4L is about right. The price has increased substantially over the last couple of years - I paid £3.45 for 5L, according to the price tag on the container I've just finished.

As to the thinning of acrylics, I posted this a while back but I use Blue Winshield Washer fluid with no problems whatsoever

Great ideas guys. I've used both acrylics and enamels since I started modeling years ago, I like both although after losing the path of enlightenment and stopping modeling for the last 15 years, I'd rather continue with my newer enamels than have to pay to replace my whole paint collection with new acrylics. Paint is expensive as hell here in the 'States, $4 per bottle for model master enamel, with Tamiya acrylics being almost $5.50

Airframes makes a very good point about spraying acrylics. Just because you can't smell something doesn't mean that it's not there. You are still creating an aerosol and there are still droplets of material in the air that you shouldn't be breathing in.
Whatever I spray, even with my very efficient extractor on, I wear a mask.

He's also right about my maths......bloody hell, you wouldn't believe that I used to be a chemist! I'm surprised I ever got anything right
The point still remains that using this sort of branded white spirit as thinners is still a very economical option and it will work perfectly well with solvent based enamels like those we have mentioned above.

Cheers

Steve

I use acylics exclusively, and exclusively tamiya paints. For thinners I use Industrial grade (ie professional....its a bit dearer, but far fewer impurities) thinners, the same as is used in spraypainting automobiles.

I dont profess to be any sort of expert, but neither can I say that any of my woes are due to paint or airbrush blockages. The biggest single problem IMO is that the acylic can get too thick, and that makes application dificult. The thinners always overcome that problem....if the paint is too thin, I can either add more paint, or apply more coats. The great advantage with acrylics is that it dries quickly....dry in a few minutes and able to have another coat applied if needed.

Parsifal, going to be picky here, acrylics CURE as chemical bonds form. Dry to the touch is not cured, about 24hr or more required and as the surface cures it blocks slovent from escaping from the under layers.

Yep.. modelling is not a race.

One thing I read years ago, if you are going to repaint, do it within an hour, something to do with the chemical reaction as Mr. Wint mentions. If you can't do it withing an hour, wait about 24hrs for the next coat to give the reaction time to run it's course.

Geo

Not all paints cure. Curing is a chemical reaction which alters the paint. Some paints simply dry by evaporation of the solvent and are typically easily removable with the original solvent. You'd need to check the brand you are using.
Cheers
Steve

Ive had problems galore with paint, but never ones relating to curing of the paint. The biggest problem I have on a repeated basis is that the paint is too thick, making application from the gun difficult. The gun either does not work at all, or, it applies the paint as these tiny globules, creating a horrible "orange peel" or "dusty" effect. Ive found the best solution to this is to apply acrylic thinner drop by drop, until I get a nice consistency in the paint. For my gear, ive found the best is to get the paint roughly the same consistency as milk. if the paint is the consistency of cream, its too thick and wont apply properly. If its the consistency of water, its too thin and will tend to run or not apply thickly enough......you get this translucent half colour that is definately not good.

The proportion of thinner to paint does vary, but is usually 25% to 50% for the tamiya paints I use and the gun I use to apply it.

Obviously paint to thinner ratios can vary, depending on the type of paint, the airbrush being used, pressure, distance etc etc. But you're quite correct in judging the viscosity - the 'rule of thumb' has always been that, if it runs down the side of the mixing container, when tested, the same way as milk would, then it's about right.
Average thinning ratios start at around 50/50, and go to around 40/60, paint / thinner, with higher thinner ratios sometimes being needed with some colours, depending on the job.

You do have to be a bit cautious when buying something to use as a thinner from DIY shops. For example you don't want anything to strong as it will melt polystyrene, there is also one modern type of white spirit (or something similar) which leaves a very fine white dusk after it evaporates both when used as a thinner and when spilt or used as a cleaner, the trouble with the DIY shop stuff is you never know exactly what you are getting. Just to be safe I now always mix my airbrush paint with a recommended enamel thinner even though it is way more expensive and a rip off, I still use the cheap stuff for cleaning my airbrush and have two pots like Airframes does for cleaning brushes etc.
Airbrush restorer is great stuff for shifting what white spirit doesn't move but be very careful when using it. I only use my airbrush restorer at times when the airbrush looks perfectly clean but is not working properly, keep it away from airbrush seals and never leave a cloth with any of it on next to a model or it will melt right through it.

Enamel paint is a term that is used to reference a paint with a hard, glossy and opaque finish. In actuality, the term "enamel paint" does not necessarily have a generally accepted or standardized definition, but historically, enamel paint has been used to refer to any type of enamel paint that is oil based and with a considerably glossy finish. They are available in several types, including oil based or alkyd based, which have the features of slower drying times in addition to being harder than that of water based enamel paints. Oil based paints are recognized by their distinguishable solvent odor properties and are easily cleaned using paint thinner or mineral spirits. Additionally, quite a few manufacturers now add varnish to oil based paints.
Drying oils are a key component of oil paint and some varnishes A drying oil is an oil that hardens to a tough, solid film after a period of exposure to air. The oil hardens through a chemical reaction in which the components crosslink by the action of oxygen (not through the evaporation of water or other solvents).. Some commonly used drying oils include linseed oil, tung oil, poppy seed oil, perilla oil, and walnut oil. Their use has declined over the past several decades, as they have been replaced by alkyd resins and other binders. These drying alkyds are also cured in air. The drying speed and the nature of the coatings depends on the amount and type of drying oil employed (more polyunsaturated oil means faster reaction in air) and use of metal salts, the so-called oil drying agents. These metal complexes catalyze the crosslinking of the unsaturated sites.
The drying time will vary in accordance with the type of enamel paint being used, the drying conditions and environmental conditions. Oil based enamels fully dry in 8 – 24 hours and dry on the inside first and then outwards. It is easy to tell when an oil based enamel has fully cured, as it will feel entirely dry when touched. For this reason, second coats are applied while the original coat is "tacky". This assures that the second coat adheres to the first coat and so on.
On the other hand, water based enamels can take up to one full month to set and can be damaged during that time, so a high degree of care should be exercised when washing and handling. Water based enamel paints will dry on the outside first and then the inside. An outer covering will form on the surface and although the paint will feel dry to the touch in approximately one hour after application, the underlying paint will still be moist. Weather plays a hand in the drying time of the paint. When there is a high degree of humidity or it is on the cool side, the enamel may take up to several weeks to cure completely.

To go slightly off topic I have noticed that diy low odour acrylic gloss paint is excellent on doors but rubbish on window sills. No matter how long you leave acrylic paint to dry on a window sill it will always attach itself to anything you put on it, it doesn't actually stick to whatever you may have put on it but it sort of grabs it.
These days we seem to be getting sold all sorts of complete and utter crap in the name of saving the planet from destruction. I don't know about outside of Europe but here you can no longer buy decent light bulbs or real creosote and even spud guns have been banned, so as someone has already said they probably will ban enamel paint as well and in the name of progress replace it with something inferior and more expensive.