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Hello dakka,

I recently started airbrushing and I'm relatively new to the process, though well informed.

The issue is, no matter what I seem to do, I consistently end up with my paint coming off to easily. At least far more easily than via brush application.

I have used Vallejo Polyurethane Black Primer and GW Black primer and both yield similar results.
(sorry in advance for wall of text - just want to give as much information as I can)

Here is what I have done so far:

Prime with Vallejo (no thinning)
Allow to dry and Cure (almost a week)
Scratch test - only with significant force from my fingernail does the primer come off
Base coat with Citadel Air (no thinning)
Allow to dry 24hours
Paint scratches off and takes primer with it.
Paint feels somewhat tacky to touch.

Prime with Vallejo (no thinning)
Allowed to dry and cure (24 hours+)
Base coat with Citadel Base paint (thinned with Liquitex flow aid/water 20:1)
Allowed to dry for an hour or 2
Layer with Citadel Layer paint (thinned with Liquitex flow aid/water 20:1)
Paint comes off with primer during normal handling, scratches off very easily back to bare plastic.
Even after a few weeks of having the paint on, same result though it feels slightly less tacky. Bare primer comes off just as easily.

GW Chaos Black from the can
Allow to dry and cure (a few weeks)
Scratch test - impossible to remove with fingernail
Base coat with Citadel Base paint (thinned for airbrushing with Liquitex airbrush medium)
Allow to dry - scratch testing every so often.
Primer does not appear to come off, if it does it's only slight not back to bare plastic, paint becomes progressively harder to take off to the point it chips off as opposed to peeling off easily.
Paint still feels tacky to the touch though less so than with the Vallejo primer

So... I'm trying to source out what may be causing the issue. I'm thinking a bad batch of Vallejo primer? Or a bad batch of Liquitex additives? Maybe the Liqutex additives cause the end result of the paint to soften despite the claims on their website of better hardening? Using brush application with flow aid/water (20:1) on GW Skull white that turned out fuzzy as it does yields similar results.

At this point I am at a loss to explain why this is going on. I was of the impression that airbrush application dries relatively quickly, I've left models sitting for weeks with no improvement to the results. I would blame the weather but other hobbyists in my area don't have issues such as this. Not even close.

Any input on this would be great, I know it's a sort of complicated problem, hence the wall of text (sorry) to give as much information as possible to assist solving the problem.

Some Vallejo primer colors are very poor. Which one are you using?

The Vallejo black primer works very well but does indeed take 2 weeks to fully cure. After that it should be scratch proof, especially when you varnish it all. GW can primer has a lot more "teeth" for sure.

I would avoid touching models with naked fingers in the first few days. Always have some sort of handle for the mini.

Thanks for the reply.

I knew Vallejo Polyurethane Black took a while to cure, but 2 weeks? Harsh :/.
That said, I have a primed part that I've left for about 2 weeks, maybe more and seemingly there has been very little improvement in it's durability.
Even less durability for the parts I have left just as long but have sprayed with a Citadel Base and Layer.

I'm doing a test run on some sprue to try and nail down the problem, I'll leave one that I've primed with Vallejo for a solid 2 weeks before touching it and see if that improves the situation.

I'll post the results here as I go along.

Thanks for the info, really appreciated.

So after some somewhat "scientific" testing, here are my results:

The parameters of my tests were as follows:

Vallejo Polyurethane Black Primer (No thinners) - Test at 12 hours for durability - Test at 24 hours for durability
GW Chaos Black Primer (No thinners) - Test at 12 hours for durability - Test at 24 hours for durability

2 coats of spray while wet were applied, Vallejo via airbrush, Chaos Black via spray can to achieve a uniform black colour.
A few minutes after application, the surface is touch dry.
GW Primer appears thicker and has a matt finish
Vallejo Primer has a satin finish

At 12 Hours:
GW Primer chips off with some force
Vallejo Primer scratches off but seems to stay a bit better than GW Primer
Both have smooth, even finishes. GW seems "rougher".

At 24 Hours:
GW Primer scratches off only on sharp edges and corners with significant force. Would likely break fingernail if not careful
Vallejo Primer is slightly softer than GW, but produces a similar result. Where the coats were thinner, it was easier to scratch off.

From here I applied Mephiston Red as a test colour... Because it's a pretty colour...

Control tests were performed the same way without primer, just on bare plastic.
As Mephiston Red Air is an "airbrush ready" paint, I thinned Mephiston Red Base to approximately this consistency for airbrush application.
Multiple passes over the parts were made until a uniform red colour appeared and the surface looked "wet" with paint.

1. Vallejo Primer - Mephiston Red Air - No thinners
2. Vallejo Primer - Mephiston Red Base - Liquitex Airbrush Medium
3. Vallejo Primer - Mephiston Red Base - 20:1 Demineralized Water and Liquitex Flow-Aid mix
4. Vallejo Primer - Mephiston Red Base - Demineralized Water

1. GW Primer - Mephiston Red Air - No thinners
2. GW Primer - Mephiston Red Base - Liquitex Airbrush Medium
3. GW Primer - Mephiston Red Base - 20:1 Demineralized Water and Liquitex Flow-Aid mix
4. GW Primer - Mephiston Red Base - Demineralized Water

Scratch tested at 12 hours:
All Control tests performed as expected. Paint scratched off easily no matter the thinner used. Liquitex Airbrush Medium performed best for adherence and durability.

Vallejo Primer:
1. Scratches off easily, primer stays unless scratched hard
2. Scratches off easily, primer comes off too
3. Scratches off easily, primer comes off too
4. Scratches off easily, primer comes off too

GW Primer:
1. Paint comes off with moderate force, extra force and primer can come off too but it chips rather than scratches
2. Paint does not come off even on corners, chips if scratched really really hard
3. Paint comes off if scratched hard, primer sometimes chips
4. Paint comes off if finger nail digs in, slightly soft about the same as flow-aid mix, primer sometimes chips

Scratch tested at 24 hours:
All Control tests performed as expected. Paint scratched off easily no matter the thinner used. Liquitex Airbrush Medium performed best for adherence and durability.

Vallejo Primer:
1. Scratches off with slightly more force than an instant lottery ticket, primer stays mostly, adherence varies across the surface
2. Scratches off with slightly more force than an instant lottery ticket, primer comes off sometimes
3. Paint scratches off a little, primer comes off sometimes
4. Paint scratches off with a fair amount of force, primer comes off too

GW Primer:
1. About the same as 12hour test, primer stays on
2. Not coming off except on corners, some moves with excessive force, paint feels a little tacky to the touch
3. Seems weaker than 12hour test, scratches off on thicker areas of coat, primer stays in place
4. About the same as 12hour test, primer stays on, takes some force to scratch off.



So the results I can take away from this test are as follows:

It would appear thinning with Liquitex Airbursh Medium over GW Primer produces the best results. However, each thinning product appeared to behave as expected despite the ability to scratch off the paint and or primer.
Airbrush Medium makes the paint harden like it should, Flow-Aid makes the paint slightly softer when compared to just water as would be expected as it does slightly extend drying time and manipulates the behaviour of the paint. The water in this mix, as would the water alone, separates the pigment and therefore creates less adhesion to the surface as would be expected.
The odd behaviour of Mephiston Red Air is what I cannot put my finger on. It should have the best adhesion overall due to the fact nothing has been added to change the paints in any way. Its Paint on Primer end. Maybe the GW Air range just works this way? Maybe the pre-thinned paint has less adhesion than the normal base range?
I think the more likely conclusion and the common factor across the board is one of, or a combination of these factors:

1. Weather - I live right on the beach and it is quite hot and humid at all times here. This will definitely impact drying times and curing times of the paint. Perhaps the act of airbrushing changes the drying time of the paints when compared to the brush? By rights it should shorten the drying time if anything...
2. Inexperience with airbrush - due to the lack of uniformity in the coats producing differing results dependant on the thickness or thinness of the coats or the thinning of the paint in preparation for airbrushing, this may also be a factor in seeing these results.
3. Bad batch of Vallejo Primer - I cannot see that the performance of this primer would be this bad. I could accept a full 24 hour wait before painting on the primer, but it scratches off even long after that. I have a part that was primed almost a month ago and even though it is harder now, the primer still comes off. Currently I am testing the theory that this primer takes 2 weeks to fully cure and I will assess the results thereafter.

All in all, I think that this problem is likely produced by my inexperience with use of an airbrush and thinning the paint in combination with the weather where I particularly paint varying drying times by far more than what I am used to, or would even reasonably expect. Any input on my findings would be great. If you live in a hot humid environment have you seen similar issues?

Again apologies for the wall of text - just wanting to provide as much information as possible. Hopefully this helps someone in a similar position to narrow down problems they are having.

Interesting testing, a couple of thoughts

bmxbandit wrote:
GW Primer appears thicker and has a matt finish
Vallejo Primer has a satin finish

How thick and how matte/gloss a spray comes out depends both on the amount of matte medium in the product but also how you spray it. A spray can will usually come out thicker simply because it sprays a much higher volume, you can combat that by not pointing directly at the model when you start spraying. Spray in "passes", start spraying to the side of the model, sweep across the model, stop spraying. The faster you sweep, the thinner the layer of paint.

Also the level of matteness depends on weather but also spraying distance. If you spray from "too far" then the paint can come out very matte, to the point of being grainy.

The reason I mention this is because surface finish is important for durability even within the same product. A primer sprayed thinly and smoothly will be tougher than the exact same primer sprayed thickly with a rough surface finish. A rough surface finish mean when you do a scratch test, your nail has something to bite in to so it's easier to scratch. On the flip side, since we're talking about primer, some roughness is desirable so that the next layer has something to bit on to. Likewise thickness is important, too thin and you can wipe the paint away, too thick and since paint is flexible it gives your finger nail something to bite in to and ends up weakening the paint.

It's a balancing act and I just thought I'd mention it because it will affect the outcome of the results and it is possibly an application issue as much as it is a product issue.

Multiple passes over the parts were made until a uniform red colour appeared and the surface looked "wet" with paint.

1. Vallejo Primer - Mephiston Red Air - No thinners
2. Vallejo Primer - Mephiston Red Base - Liquitex Airbrush Medium
3. Vallejo Primer - Mephiston Red Base - 20:1 Demineralized Water and Liquitex Flow-Aid mix
4. Vallejo Primer - Mephiston Red Base - Demineralized Water

1. GW Primer - Mephiston Red Air - No thinners
2. GW Primer - Mephiston Red Base - Liquitex Airbrush Medium
3. GW Primer - Mephiston Red Base - 20:1 Demineralized Water and Liquitex Flow-Aid mix
4. GW Primer - Mephiston Red Base - Demineralized Water

Scratch tested at 12 hours:
All Control tests performed as expected. Paint scratched off easily no matter the thinner used. Liquitex Airbrush Medium performed best for adherence and durability.

Vallejo Primer:
1. Scratches off easily, primer stays unless scratched hard
2. Scratches off easily, primer comes off too
3. Scratches off easily, primer comes off too
4. Scratches off easily, primer comes off too

GW Primer:
1. Paint comes off with moderate force, extra force and primer can come off too but it chips rather than scratches
2. Paint does not come off even on corners, chips if scratched really really hard
3. Paint comes off if scratched hard, primer sometimes chips
4. Paint comes off if finger nail digs in, slightly soft about the same as flow-aid mix, primer sometimes chips

Scratch tested at 24 hours:
All Control tests performed as expected. Paint scratched off easily no matter the thinner used. Liquitex Airbrush Medium performed best for adherence and durability.

Vallejo Primer:
1. Scratches off with slightly more force than an instant lottery ticket, primer stays mostly, adherence varies across the surface
2. Scratches off with slightly more force than an instant lottery ticket, primer comes off sometimes
3. Paint scratches off a little, primer comes off sometimes
4. Paint scratches off with a fair amount of force, primer comes off too

GW Primer:
1. About the same as 12hour test, primer stays on
2. Not coming off except on corners, some moves with excessive force, paint feels a little tacky to the touch
3. Seems weaker than 12hour test, scratches off on thicker areas of coat, primer stays in place
4. About the same as 12hour test, primer stays on, takes some force to scratch off.

Interesting results.

What this tells me (if I'm understanding your description of the strength of the paint) is that the solvents in the paint (for the Air paint) and thinners (for the Base paint) are attacking the primer layer, more so for the Vallejo primer than the GW primer.

It's not a bad thing if the solvent in the paint slightly eats in to the previous layer, SLIGHTLY, so that it sticks better. But when it attacks it in a big way it compromises the strength of the previous layer.

You said "Multiple passes over the parts were made until a uniform red colour appeared and the surface looked "wet" with paint.". I assume this means you were spraying wet on wet until you got a nice solid coat. That's not necessarily a bad thing, but if the solvents in your top layer are attacking your bottom layer too much, it may be better to apply a thin coat, let it flash off (the solvents evaporate and it *looks* dry (not cured, just that it looks dry, should only take a few seconds for most paints if you apply it thin enough)). That way, the solvents don't get trapped quite so easily, so will have less of a chance to attack the underlying paint.

Of course.... I came to the conclusion Vallejo primer sucks ages ago and swapped to lacquer based primers I think I mentioned it in another thread, Vallejo primer is just not tough, which when painting miniatures is one of the main reasons to apply a primer in the first place.

Lacquer based primers have their own issues with applications (the fumes are more unhealthy, you need good ventilation, also the solvents in lacquer based products tend to attack rubber seals so your airbrush should use teflon seals in locations where that could cause problems down the track such as the needle packing seal).

As far as I'm aware there's simply no airbrush primers that are tough and not either a lacquer or an enamel. If someone knows one, I'd give it a go.

The toughest acrylics I've come across that I'd consider using as a primer are tamiya acrylics, but even then I tend to thin them with lacquer thinners.

3. Bad batch of Vallejo Primer - I cannot see that the performance of this primer would be this bad. I could accept a full 24 hour wait before painting on the primer, but it scratches off even long after that. I have a part that was primed almost a month ago and even though it is harder now, the primer still comes off. Currently I am testing the theory that this primer takes 2 weeks to fully cure and I will assess the results thereafter.

That's a possibility, I wondered if my Vallejo primer was a bad bottle as well, but after googling and seeing a lot of people having similarly poor results I concluded even if I did get a bad bottle, it wasn't worth pursuing it and lacquer primer is simply better.

Thanks for the reply, great info.

However, now after passing on the airbrush for a little while to get my space wolves going I am having the same problem brushing on.

Just used GW primer. Left it a full 24 hours to cure, painted 2 thin layers of "The Fang" and 2 thin layers of "Russ Grey" with plenty of drying time between (a few hours between layers, and a few days between colours) and it comes off just as easy.

I now have no idea what is going on. I thin the paint with Liquitex Flow Aid with water 20:1 as described which loads of other people do with no adverse results. GW paint on GW primer which I have had absolutely no issues with before, I mean I can beat the crap out of other models and I'm lucky to take off one layer of colour let alone hit primer, or plastic for that matter.
There shouldn't be a problem with GW paint attacking GW primer, the flow aid could be, but with so many people using it on GW stuff and others with no issues makes me doubtful...

I can only think that perhaps the dish soap I used to clean the parts left a residue? That said, I've always used dish soap to clean the parts, just whatever came to hand at the time. Perhaps this particular one is causing issues...

Guess it's back to testing... I'll post the results when I can. Anyone with additional info or thoughts?


Automatically Appended Next Post:
Also to note: GW primer was applied in multiple passes, thinly, from a reasonable distance, no visible drying of the paint mid air, not to thick either.

Paint was brushed on with GW Small layer brush, from a wet pallet in thin even coats with plenty of drying time between coats as I've always done.

Not that I'm an expert, but the same process has worked before and the above seems to be the general consensus in "how to apply paint". Just to clear up any application issues from the equation.