acrylic on top of enamel what's the score

[Simon Moore]

Hi all

 

Recently I read an article by Pelle Soeborg about weathering his American outline locos. It spured me on to try some of his techniques with a Kato Dash 9 in union pacific livery. I ordered some of the paints & varnish that Pelle described in his article & read it through a couple of times to be sure I understood it properly. Pelle makes up some modelmaster enamels into washes for the weathering but seals the paint with vallejo matt acrylic varnish which raises questions for me. I once applied acrylic on enamel or visa versa (can't remember which way exactly ) & the paint had a reaction causing a bubbling / veining effect.

Before I go ahead & weather a model with a process I've not done before I wanted to make sure it was right because I don't wish to ruin a perfectly good model especially after putting work into it as well. I'd there anything I need to be careful of with this process ????

 

Cheers

 

Simon

[AngryMeerkat]

The 2 types of paint are fine to be used together as long as each application is allowed to dry fully.

 

Typically when painting a model I use thinners based primer, acrylic paint, enamel gloss varnish, a mix of acrylic and enamel weathering, all sealed with acrylic matt varnish. As long as each stage has at least 24 hours drying time then there are no problems.

 

Mark

[Simon Moore]

Thanks for that Mark I was a little concerned. Looking forward to trying the mix now & seeing what these paints are like.

 

Simon

[garethashenden]

Let it dry for a few days, not just until it is touch dry.

[Pugsley]

Whilst you may get funny looks from others in your household, the sniff test will tell you if it's safe to put a coat of acrylic over enamel.  If you can still smell thinners, then leave it until you can't anymore.  That doesn't work the other way round, but acrylics dry much quicker, so you're usually good to go after 24-48 hours.

[Simon Moore]

Martin my girlfriend would probably just walk past if she saw me sniffing a model. She's used to me by now but thanks for the tip ; )

[Jeff Smith]

Cellulose over enamel will probably react and cause wrinkling of the enamel.  I remember years ago this happening on a Honda 50; I had used an enamel undercoat and official Honda cellulose top coat.......I believe you can put anything over cellulose as long as it is dry - I've heard of people using Halfords's (or similar) car cellulose as their base colour - probably only good on brass or white metal though! 

[AngryMeerkat]

Cellulose paints have been pretty much phased out now, there are better/safer/cheaper paints so celly just has no place in the market. I think I last used celly about 8 years ago, as the company I was working for were one of the last in the automotive industry to move over to water-based systems. I'm pretty sure all the aerosol cans now use something other than cellulose for H&S reasons, but will happily be corrected on this as apart from primer I don't use aerosols.

 

As for certain paints only being used over metal - a common misconception I'm afraid. Each stage of painting is designed to bond to the stage before it, not the substrate. Varnish or lacquer can be applied over any paint you choose. Paint can be applied over any primer you choose. It's the primer that matters as primers are designed to bond to different substrates. Choose the primer that's suitable for the material you are working with (acid etch for most metals, bonding aid for most plastics) and use the colour and sealer that you are most comfortable with and you won't go far wrong.

 

Mark

[RBE]

Halfords car sprays are all acrylic based nowadays. I believe that there is a law in place (I may be wrong) now that prohibits the sale or cellulose based aerosol paints to the general public (although I'm sure there are places you can get the stuff). I use Halfords primer on pretty much everything with no ill effects (it does not however like going over enamel (I would assume the colours to be the same but I don't use them) it WILL bubble and crinkle if you do regardless of whether the enamel is dry or not)

Edited June 26, 2014 by RBE

[Phil Bullock]

If you want to use enamel washes over enamel base coats then try thinning wash with turpentine substitute rather than enamel thinners - far less likely to attack the base coat. Might dry slightly glossy so a final seal of matt varnish will finish the job....

 

Phil

[TheWeatheringMan]

If you want to use enamel washes over enamel base coats then try thinning wash with turpentine substitute rather than enamel thinners - far less likely to attack the base coat. Might dry slightly glossy so a final seal of matt varnish will finish the job....

 

Phil

Hi All,

Don't do this under any circumstances - you will be courting potential disaster on your models.

Turps Substitute is not and has never been intended to be a paint thinner.

To use this to thin paint can and often will destroy the paint make up by causing the binder to cease to bind or the dryers to cease to cause drying.

It might just work in some washes as these are not paints in the conventional sense but to use Turps Substitute in paint is very risky and can very easily result in problems with the paint coat that cannot be overcome without destruction of the model.

There is also the fact that the nature of Turps Substitute will also be very likely to cause chemical damage to the underlying plastic due to solvent attack - turps substitute does not 'flash out' from the paint layer like white spirit as its less volatile and so remains active within the paint film far longer and thus is likely to attack the plastic.

Turps Substitute is basically rubbish left from another process that has little use other than cleaning brushes due to its solvent nature.

Due to what it can contain Turps Substitute is totally unsuitable as a paint thinner - please don't use it for that - the risks can totally ruin a model.

As a trained paint and solvent chemist this is something I've been asked about many times - as a modeller I've seen the results that can happen.

Regards

[Killybegs]

Hi All,

Don't do this under any circumstances - you will be courting potential disaster on your models.

Turps Substitute is not and has never been intended to be a paint thinner.

To use this to thin paint can and often will destroy the paint make up by causing the binder to cease to bind or the dryers to cease to cause drying.

It might just work in some washes as these are not paints in the conventional sense but to use Turps Substitute in paint is very risky and can very easily result in problems with the paint coat that cannot be overcome without destruction of the model.

There is also the fact that the nature of Turps Substitute will also be very likely to cause chemical damage to the underlying plastic due to solvent attack - turps substitute does not 'flash out' from the paint layer like white spirit as its less volatile and so remains active within the paint film far longer and thus is likely to attack the plastic.

Turps Substitute is basically rubbish left from another process that has little use other than cleaning brushes due to its solvent nature.

Due to what it can contain Turps Substitute is totally unsuitable as a paint thinner - please don't use it for that - the risks can totally ruin a model.

As a trained paint and solvent chemist this is something I've been asked about many times - as a modeller I've seen the results that can happen.

Regards

 

I'm confused! This is an extract from Wikepedia -  'In western Europe about 60% of the total white spirit consumption is used in paints, lacquers and varnishes. White spirit is the most widely used solvent in the paint industry.' Do your comments above apply specifically to enamels?

[TheWeatheringMan]

I'm confused! This is an extract from Wikepedia -  'In western Europe about 60% of the total white spirit consumption is used in paints, lacquers and varnishes. White spirit is the most widely used solvent in the paint industry.' Do your comments above apply specifically to enamels?

Hi,

I'm not sure what you are confused about unless its the common mistake of thinking that White Spirit is the same substance as Turpentine Substitute.

White Spirit is the solvent in most common solvent borne paints including enamels.

Turps Substitute is an entirely different material that is not at all suitable for thinning paints - ANY PAINTS!.

Turps Substitute is as previously explained basically the rubbish that is left over during a refining process and has virtually no use except as a cleaner for brushes and other equipment. Because Turps Substitute is able to dissolve White Spirit based paints it can be used to clean equipment but it must not be used to thin paint for spraying due to its chemical action on the formulation of the paint.

Basically :  White Spirit = refined petroleum product (light hydrocarbon oil) = thinning paint

               :  Turpentine Substitute = left over rubbish from refining = cleaning brushes etc. ONLY.

               :  Pure Turpentine/Gum Turpentine = natural product from tree resin used to thin/mix oil based paints as used by artists - can be used to thin enamels

 

The use of Pure Turpentine in enamels is good when spraying gloss finish as it does not effect the gloss level in the way White Spirit can.

Just to repeat what I've said before : never buy a so called 'enamel thinners' from a model shop - all you are doing is buying a very very expensive small container of White Spirit - go to a DIY shop and buy White Spirit from the paint counter - if you want to be absolutely sure check the label to see that the White Spirit conforms to B.S. 245 - this means it meets a standard that is strictly controlled.

 

One last point regarding Turpentine Substitute - it can contain a proportion of water - imagine thinning Humbrol / Railmatch or Precision enamels from the kitchen tap and consider the effect.

That's one of the reasons its unsuitable for thinning paint!.

 

Hope that helps.

Regards.

Edited July 9, 2014 by TheWeatheringMan

[micklner]

I have used enamels for years and thin with turps and never had a problem or have ever heard of such problems before.

Edited July 9, 2014 by micklner

[Killybegs]

Well, I guess we have to take Wikepedia with a pinch of salt as, according to them, turps sub is white spirit.

[alfsboy]

Its not the actual paint that can cause issues but the thinners it uses .The Halfords sprays still use Xylene type thinners and its this that causes the problems .Basically as others have said cellulose / xylene will attack enamel paint and styrene but not ABS plastic .i know this from bitter experience .

[TheWeatheringMan]

Well, I guess we have to take Wikepedia with a pinch of salt as, according to them, turps sub is white spirit.

Hi,

remember that Wikipedia contains a great deal of articles placed there by people who dont always know or check their facts.

 

I am a fully qualified paint and solvent research chemist trained at one of the worlds largest paint and solvent manufacturers.

 

To clarify once and for all :

 

White Spirit is a light hydrocarbon oil that in this country is required to meet the specifications laid down in British Standard 245.

White Spirit is used by far and away in the largest part as both a component in some types of paints and as a paint thinner (particularly for spraying)

 

Turps Substitute is NOT, NEVER HAS BEEN AND NEVER WILL BE the same liquid.

 

Turps Substitute is the left over rubbish from a refining process.

Many years ago when many paints were of the traditional oil based type ie. heavy and relatively thick they were made up by grinding pigment into oil (oil gave the paint its gloss), this was then thinned with pure turpentine which was (and still is) distilled from wood resin. Other ingredients were added to the paint mix such as binder (to keep the mix from 'splitting' and dryers (for obvious reasons and the source of lead in paints of that era) and 'talc' to reduce the gloss to a satin or matt (flat) finish if required.

As the cost of producing pure turpentine rose a search was made for a 'turpentine substitute'.

It was found that a by-product of refining that had little or no other use could be used in place of pure (or real) turpentine.

This product therefor came into use and in everyday language as turpentine substitute (logical) as it was used to substitute for pure turpentine (it also became known as 'turps' in common parlance but strictly speaking the term 'turps' should only have ever been used as a shortening of 'Pure Turpentine').

 

White Spirit is a much purer, low volatile solvent that is deliberately refined from petroleum products.

 

As the chemistry of paint moved on the use of the impure 'substitute' became less common as new paint formulations were based around the use of synthetic pigments and White Spirit. 

 

The substitute liquid has continued on sale as it offers a cheaper alternative to White Spirit FOR CLEANING BRUSHES ETC. and of course little other use can be found for the liquid.

 

So once again it must be clearly understood that Turps Substitute (or Turps) is not the same thing as White Spirit - they are as different to each other as Water and Diesel.

 

As I said in my previous post Turps Substitute can contain a proportion of water - I'm sure that most people will understand the effects of putting water into an enamel paint. If not get a tin of conventional gloss decorating paint and put some tap water into it. You will soon see why Turps Substitute is not intended for or suitable for paint thinning.

Of course Turps Substitute does a good job of cleaning paint from brushes because it is a solvent that will mix with the paint - this does not however make it suitable for thinning - petrol will clean paint from brushes for the same reason but would you thin your paint with it - to do so will not only badly effect the make-up of the paint but will also open up a whole new can of worms (poison, cancer, explosion to name a few).

 

As to a modeller saying that he has thinned paint for years with 'turps' - all I will say from an experts point of view is that a person has been very lucky if he is actually using 'turps substitute' and it has always worked.

Make no mistake - I'm not saying it wont work because I know it can - 'turps substitute' is after all a solvent of the paint (or it wouldn't clean brushes) but what it can do to a white spirit based paint could result in the total ruin of the model. Turps Substitute can also more readily attack the plastic the model is probably made of due to what it can also contain.

 

What I said in my first post was that thinning paint with 'turps substitute' is very unwise for the above reasons - and all I would ask is why take a totally unnecessary chance when White Spirit to BS 245 is freely available and cheap on the high street.

 

To cover the Halfords thinner - yes this does contain Xylene (an aromatic hydrocarbon). This is more to do with the painting methods used in the automotive refinish field where the need for the paint solvent to 'flash out' quickly is uppermost.

This may seem to contradict the statement that Halfords paints are now acrylic.

This is because there are several different types of acrylic paint and not all are water based as most modellers have come to understand (such as the Railmatch range)

There are 'acrylics' that use modern acrylic pigments but are still a solvent based paint - Halfords paint is of this type hence the use of a thinner containing Xylene.

And yes to confirm what another poster said the xylene WILL attack enamel (even long dried) in the same way that the old cellulose paints and thinners did.

 

Xylene can be used to thin White Spirit based enamels to speed up the 'flash out' of the solvent in the paint to enable quicker 'coat on coat' build up of the colour with less risk of runs.

Precision Paints used to sell (they may still) a 'rapid flash' thinner - this was nothing more than neat xylene.

However I'd advise very great caution doing this as Xylene is carcinogenic, the vapour is highly explosive and being a light hydrocarbon is also a very good and fast acting solvent (dissolver) of polystyrene - need I say more.

 

I really do hope the above has clarified the matter of 'Turps Substitute' versus White Spirit.

 

My only interest in answering the original question was that I felt able to offer my expertise to fellow modellers in the earnest hope I might save a fellow modeller from a painting disaster.

Sometimes I think its all in vain when it gets contradicted in a way that might just lead a modeller into that very disaster - but hey, that's life I suppose.

 

I really do hope this long winded post might just be of interest to someone and if it helps you too i'll be happy.

 

Best Regards

 

 

 

PS.

I have not commented on differing primers for differing surfaces as the post from my fellow expert from the automotive field 'Angry meercat' is spot on correct in what he says - I know that his advice in this respect is correct because he works in the practical side of paint application if I may put it that way.

Edited July 9, 2014 by TheWeatheringMan

[AngryMeerkat]

TheWeatheringMan-

 

Your advice, as always, is very much appreciated. Please continue to share your knowledge despite the 'amateur professionals' contradicting the subject you've obviously studied and worked in great depth. Despite 15+ years working in the application side of the trade I still learn a great deal from your posts! I know the how but it's nice to learn more of the why, and sometimes more important, the why not.

 

Unfortunately I'm currently working with one of the amateur professionals, the type that know it all. My latest contract has taken me to a yacht builder, the interior finishing department. I was very quiet when I started, not wanting to appear cocky, and listened to this young lad proceed to tell me how to paint and polish wood and how I was doing it all wrong. After 3 weeks I finally lost my patience, and asked him how long he's been working with paint. "I started here a week before you, so I've had a week more training and practice. You've only been doing the job 3 weeks but you think you know more than me". At that point I really did lose it, and he got both barrels! He now realises that after 3 weeks he knows absolutely nothing of paint or finishing, and trying to tell someone 12 years older and with 15 years more experience how to do the job probably wasn't his best move!

 

But people like that are everywhere, and the internet has given them power. All you can do is offer your experience and hope those with a genuine interest will take note of it.

 

Mark

[TheWeatheringMan]

TheWeatheringMan-

 

Your advice, as always, is very much appreciated. Please continue to share your knowledge despite the 'amateur professionals' contradicting the subject you've obviously studied and worked in great depth. Despite 15+ years working in the application side of the trade I still learn a great deal from your posts! I know the how but it's nice to learn more of the why, and sometimes more important, the why not.

 

Unfortunately I'm currently working with one of the amateur professionals, the type that know it all. My latest contract has taken me to a yacht builder, the interior finishing department. I was very quiet when I started, not wanting to appear cocky, and listened to this young lad proceed to tell me how to paint and polish wood and how I was doing it all wrong. After 3 weeks I finally lost my patience, and asked him how long he's been working with paint. "I started here a week before you, so I've had a week more training and practice. You've only been doing the job 3 weeks but you think you know more than me". At that point I really did lose it, and he got both barrels! He now realises that after 3 weeks he knows absolutely nothing of paint or finishing, and trying to tell someone 12 years older and with 15 years more experience how to do the job probably wasn't his best move!

 

But people like that are everywhere, and the internet has given them power. All you can do is offer your experience and hope those with a genuine interest will take note of it.

 

Mark

Hi Mark

Thankyou very much for your reply.

I too have worked with the 'expert' who had learnt all there is to know in a few months - in that case it was on a heritage railway and his 'knowledge' ended up costing that railway several thousands of pounds and over 400 man hours to put right the 'benefit' of his 'knowledge'.

I have always found it a real pleasure to have tried to help fellow modellers making use of my training etc. and yes of course i'll continue to do so.

Over the very many years I've been active in the hobby we have seen a large number of 'wonderful discoveries' from people that have turned out to cause nothing but problems in the longer term - helping to prevent fellow modellers falling into such traps is, in my eyes at least, very worthwhile and a part of the friendship within the hobby.

Best Regards

[Jeff Smith]

Drifting off topic a bit I'm interested about the different types of acrylic model paint.  Polly Scale from Testors has been discontinued - I used to thin these with the Testors acrylic thinner rather than water; the Acryl range continues which I believe is the same formulation but aimed at non-model train usage.  There are other ranges of acrylic colours available in the US, Badger MODELflex , Vallejo and MicroLux (from Vallejo) and the Games Workshop range, and I'm wondering how important it is to use thinners from the individual ranges or whether just water is Ok?

[TheWeatheringMan]

Drifting off topic a bit I'm interested about the different types of acrylic model paint.  Polly Scale from Testors has been discontinued - I used to thin these with the Testors acrylic thinner rather than water; the Acryl range continues which I believe is the same formulation but aimed at non-model train usage.  There are other ranges of acrylic colours available in the US, Badger MODELflex , Vallejo and MicroLux (from Vallejo) and the Games Workshop range, and I'm wondering how important it is to use thinners from the individual ranges or whether just water is Ok?

Hi,

As a general rule these types of acrylic all have essentially the same or similar formulations and a thinners for any of them would work without a problem in any other brand -to which can be added Humbrol , Railmatch and Precision Acrylics.

The use of water is normally perfectly ok provided the water is fairly pure.

Its best to use distilled water if possible but purified water (from a pharmacy) or deionised water (as used for steam irons etc) comes a close second.

If you have a water filter jug at home use water from this or even boiled water left to go cold (and yes you can boil water and yet it be cold in the right place !!).

This is because the minerals in most tap water (not to mention the chemicals we are force fed by the water companies) in tap water can react with the paint formulation and cause problems - most common being adhesion problems.

Some acrylic thinners contain a trace of isopropyl alcohol to act as a 'wetting agent' for the paint so a drop into the thinning medium can help but its not essential.

Put simply, if the paint is a water borne material then any thinners for that family of paints will work.

Hope that is of interest and answers your question.

Regards

Edited July 10, 2014 by TheWeatheringMan

[Jeff Smith]

Thanks TheWeatheringMan, that's very useful.

[TheWeatheringMan]

Thanks TheWeatheringMan, that's very useful.

Hi,

You are most welcome, pleased to have been of help.

Regards

[AngryMeerkat]

Hi,

As a general rule these types of acrylic all have essentially the same or similar formulations and a thinners for any of them would work without a problem in any other brand -to which can be added Humbrol , Railmatch and Precision Acrylics.

The use of water is normally perfectly ok provided the water is fairly pure.

Its best to use distilled water if possible but purified water (from a pharmacy) or deionised water (as used for steam irons etc) comes a close second.

If you have a water filter jug at home use water from this or even boiled water left to go cold (and yes you can boil water and yet it be cold in the right place !!).

This is because the minerals in most tap water (not to mention the chemicals we are force fed by the water companies) in tap water can react with the paint formulation and cause problems - most common being adhesion problems.

Some acrylic thinners contain a trace of isopropyl alcohol to act as a 'wetting agent' for the paint so a drop into the thinning medium can help but its not essential.

Put simply, if the paint is a water borne material then any thinners for that family of paints will work.

Hope that is of interest and answers your question.

Regards

Just to add to the excellent response above. The chemicals present in tap water can cause corrosion and blockage issues with airbrushes due to the heavy chemicals and very fine tolerances involved, and is more of an issue in hard water areas. I've found de-ionised water to be a good balance between clean water and cheap price, £2 for a 5L bottle in places like The Range has lasted me nearly a year so far. The addition of a retarder or wetting agent is also recommended for most acrylics, as they can dry on the airbrush tip causing more blockages and frustration.

 

Mark

[Daddyman]

Just to add an update on this: I painted a loco with Humbrol enamel yesterday at about 6pm. I wasn't happy with the finish and decided to go with Halfords' black aerosol instead. I had a look at this thread and it seemed divided as to whether Halfords' paints would attack the enamel. Obviously, after only 14 hours in the airing cupboard, the model still smelled of thinners, but I need to get it finished by the end of the week, so couldn't wait. I reasoned that it would be quicker to see if the Halfords' paint attacked the Humbrol, and if it did, to strip everything rather than to wait for the thinners smell to disappear.

 

Then I had a thought: I wondered if the Simoniz primer would go on top of the Humbrol, and act as a "translator" coat for the Halfords' black. (I knew for sure Halfords' paint is fine on top of Simoniz within 30 mins.) So 14 hours after applying the Humbrol, with it still smelling of thinners, I applied Simoniz. And it was absolutely fine - no attack on the Humbrol.