Acrylic paint incompatibility

[Smithy1961]

Late last week I finished the 'Grape' scheme on my 1/48th F-5E using Vallejo Model Air with no problems. On Monday I used Tamiya XF-1 on the nose cone after masking of the front of the plane. Today I tried to touch up with a brush using XF-1 and encountered some'bleeding' with the Vallejo paint. Given the 48 hour break, is it possible this wasn't enough time for the Vallejo paint to cure? When spraying the XF-1 there wasn't an issue. Please forgive if this has been asked before, but I have recently returned to the hobby after 40 years and I'm new to acrylics and airbrushing. 

[Troy Smith]

Hi

Vallejo is a latex type acrylic  (along with Humbrol, Revell, Xtracrylix ,Lifecolour) If you leave some to dry out it goes rubbery. 

Tamiya is a a different type of acrylic, laquer is perhaps the term  possibly.(Gunze as well)    Anyway they are not intermixable types.

 

By this I mean you can thin Tamiya with cellulose thinners and spray.  Add cellulose thinners to Vallejo and it turns into gloop apparently.

 

 i have used Tamiya as a base coat as it has more 'bite' and then brushed Xtracylix over the top.

 

I think that the Tamiya is 'hotter' than the Valljo and is dissolving it as brushing tends to be thicker., while airbrush it would drive off some of the solvent and dry it faster would be my theory.

 

As an aside,  Tamiya will brush well if you thin with water, without and it can drag and start to lift itself when you brush back over.

  I have a tiny 1ml syringe, I suck up 0.95 ml distilled water and 0.,05 ml of W&N flow improver, shake, and the use a little pallette,  add some Tamiya, and add tiny drops of the mic until the paint flows well,  it then brushes and doesn't lift itself as brushing neat Tamiya can do.

It still dries really fast, and you can recoat fast as well without it lifting.

 

I think there have been threads on acrylic paint types here...let me see ...no, not finding anything more than the above. 

 

HTH

 

[Corsairfoxfouruncle]

9 hours ago, Smithy1961 said:

Given the 48 hour break, is it possible this wasn't enough time for the Vallejo paint to cure?

Ive done it with 24 hour break the trick is i use a clear coat between the colors. Its up to you some say thats bad for panel lines but ive never had an issue doing it. 

Edited July 16, 2020 by Corsairfoxfouruncle

[Ray_W]

10 hours ago, Smithy1961 said:

Please forgive if this has been asked before, but I have recently returned to the hobby after 40 years and I'm new to acrylics and airbrushing. 

No problem, when I came back into the hobby, the plethora of different paints and chemical compositions was the challenge.

 

@Troy Smith Troy's explanation is, as usual, excellent.

 

If I can add a couple of points.

 

The term "acrylic" is now a very confusing one.

 

In simple terms paint has 3 components - Pigment (colour), Binder (what holds the colour in place, often called "resin") and Solvent (gets it to a condition where you can apply it - brush, spray, trowel, drying time, re-coat, useage whatever). The term "acrylic" refers to the binder being an Acrylic Polymer Emulsion, that is a synthetic (man-made) binder. It does not mean washes out in water, as it has come to mean. More correctly, it is a man-made binder that can be designed and engineered to wash out in water. This is the beauty of the synthetic (acrylic) binder. It opens up a range of performance options based on the engineered binder chemical composition depending on what is required. For example: toughness, drying time, toxicity, ability to wash out in water and the list goes on. It is much more complex than the old enamel which uses a colour (pigment), linseed oil (binder), turpentine (solvent). I would suggest that nearly every modelling paint we use would be an "acrylic", that is with an acrylic polymer emulsion binder (except an "enamel" although there are enamels with an acrylic binder), but, with a huge difference in performance, compatibility and the solvent required. 

 

What does this mean for the modeller? 

 

1. Because the binder may be chemically different between brands, acrylic paints do not necessarily mix. Note that even the "latex" paints use a synthetic latex, a polymer emulsion binder and could have different binder properties between each brand.

 

2. The strength of the paint and its bond will vary between manufacturers unless the binder is close to being the same. So you may lay down some Vallejo paint then use a different acrylic that has an inherent more aggressive solvent than water, airbrush it over the top with no troubles but with mechanical scrubbing (brushing) start having issues.

  

3. In my experience, paints are compatible when fully dryed or cured depending on the thickness of the top coats and interaction between the solvent applied and the coats underneath and the potential mechanical handling. Note that this is a complex subject, so many things to go wrong. Most is learned the hard way - experience. @Corsairfoxfouruncle   Dennis's advice is on the money. Using a clear coat to protect. I use Lifecolor and have gone over it with a very aggressive solvent based clear coat Gunze GX112 with Mr Levelling Thinners before decalling more GX112, enamel washes and paint details. No issue. But, plenty of time between coats. If its latex binder I like to leave them days and then at least 48 hours further after the GX112 is applied and also thin coats of the aggressive solvent based top coat. Even using a hairdryer to speed the solvent removal so it does not attack what it is covering. I am most worried about difference in drying time and potential crazing related to different paint shrinkage rates. Also, the water based solvent paints might still be soft under the top coat and willingly accept a fingerprint. Ask me how I know.  Handle carefully.  

 

So why not all water based? Well strength and drying time. Tamiya has recently released a "lacquer" range. More confusion. Why have they released such a range of paints that needs a more aggressive "lacquer"  solvent. Important: it still uses an acrylic binder but will not wash out in water. Why? Fine pigment, rapid drying time, tough coat with the trade-off of higher toxicity, flammability, stink, more complex cleaning.  So Why? Some modellers prefer this performance.  AK Real Colors, is another relatively new range. Yes they are acrylic but they do not wash out in water, they are more similar to the Gunze and Tamiya Aqueous ranges (so called acrylics) and all three brands can be mixed but need a "hotter" solvent than water for the acrylic binder if the AK is mixed with the Gunze and Tamiya.

 

After all that, simply put, the term "acrylic" refer to the paint binder that has been designed based on the manufacturer's performance criteria. It does not mean  necessarily that it washes out in water. Check the solvent compatibility. Mechanical bond and performance between different paints is challenging. Handle carefully - plenty of drying, may need protective coats.

 

Ray

 

 

 

 

[ckw]

All of the above is why - for the most part, I've gone back to enamels ... Colourcoats, Xtracolor and (in a pinch) Humbrol. Yes the drying time is longer, but on the whole easier to thin ... with predictable results ... consistant finish, can spray or brush. I do still use acrylics - mostly for small detail work.

 

No doubt you can get excellent results with acrylics, and, if it was possible to stick with one brand, I'd probably do that - but as I find that the colours I need are not readily available in any one range, it means constantly adapting to the various 'quirks' of different paints.

 

I know where I am with enamel!

 

Cheers

 

Colin

[MikeC]

14 minutes ago, ckw said:

No doubt you can get excellent results with acrylics, and, if it was possible to stick with one brand, I'd probably do that - but as I find that the colours I need are not readily available in any one range, it means constantly adapting to the various 'quirks' of different paints.

I use Tamiya and Mr Hobby Aqueous - they can be intermixed, and Tamiya X20A thinner works with both.  Any colour I can't get, I mix.  Plenty of resources out there - eg IPMS Stockholm - for suggested mixes.

 

I've pretty much limited my stock to those two brands now: makes life much easier.

[Ray_W]

9 minutes ago, ckw said:

it means constantly adapting to the various 'quirks' of different paints.

I think being able settle on a type is important. If you can. Yes I have a preference with Gunze and Tamiya Aqueous ranges although as I often set up camp in different places on the planet it depends on what is available. So I have got to use a broad range of different supply.

 

Also apologies to any chemists reading my previous post for not mentioning alkyd polymers and the difference with acrylic polymers.     

[Troy Smith]

On 16/07/2020 at 09:11, ckw said:

Yes the drying time is longer,

 

There is/was a fascinating youtube video by @Jamie @ Sovereign Hobbies  of him painting a Mustang with Colourcoats, using their own thinner,  low pressure and close up,  and the solvent flashed off nearly instantaneously, paint being touch dry very quickly. 

 

The important part was the correct thinners, I believe this is a refined naptha type specifically adjusted for the paint,   with the added advantage that paint thinned with the compatible thinners can then be returned to the tin.

 

White Spirit is greasy gunk compared,  fine for clean up, but a false economy for thinning paint.  Jamie has said the use of white spirit is part of the reason enamels have a bad name! 

 

as an aside,  these are hydrocarbons, and their volatility  corresponds to the amount of carbon atoms in the molecule,  the more carbon, the heavier and less volatile, for example,  white spirit is like paraffin, around a C-15 molecule,  Naptha is around C-8,   lighter fuel is C-6,  and diesel is C-30.

 

I use acrylic as I really do not like the solvents,  used them as  child/teen happily,   but having done large scale paining around the house with oil paint, I really got to dislike the solvents and clean up, and now use acrylics instead if I can.  

 

In short acrylic work better thinned with water until they flow really smoothly,  and flow improves helps as it breaks down the surface tension of water.

Water is so common a chemical that folks forget it's actually a really unusual compound in chemical terms, with many odd properties.....

I digress as usual....

 

 

[ckw]

On 18/07/2020 at 01:43, Troy Smith said:

paint being touch dry very quickly.

Yes this is true - but the operative words here are 'touch dry' ... I certainly wouldn't overcoat it until it has had time to cure. I'm not sure exactly how long is needed and the would be a number of variables affecting this (temperature, humidty, paint thickness). I allow 6 hours and have had no problems, but that's not to say it needs 6 hours. I do use colourcoats thinner.

 

Ultimately in my early days I lost count of the number of models ruined through not leaving paint to dry. I've just incorporated adequate drying time into my workflow ... which entails working on multiple models at the same time.

 

Cheers,

 

Colin

[Jamie @ Sovereign Hobbies]

39 minutes ago, ckw said:

Yes this is true - but the operative words here are 'touch dry' ... I certainly wouldn't overcoat it until it has had time to cure. I'm not sure exactly how long is needed and the would be a number of variables affecting this (temperature, humidty, paint thickness). I allow 6 hours and have had no problems, but that's not to say it needs 6 hours. I do use colourcoats thinner.

 

Ultimately in my early days I lost count of the number of models ruined through not leaving paint to dry. I've just incorporated adequate drying time into my workflow ... which entails working on multiple models at the same time.

 

Cheers,

 

Colin

 

I wouldn't brush over it, but I routinely mask over the top and spray other colours immediately after the airbrush is flushed through.  I don't have the patience to wait for stuff to dry...