Airbrushing - What am I doing wrong?

[6029 King Stephen]

I am sure there are hundreds of threads already on this subject but please bear in mind that I am currently based in Cameroon, West Africa and do not have the advantage of any modelling shops in the country, let alone in the capital where I am based.

 

I first starting airbrushing in about 1991 with a basic humbrol bottom feed brush that worked off a gas canister.  Results were a bit hit and miss and canisters cost me a small fortune.  Fast forward to 2006 when I was living in Athens and following advice on this forum I decided to try my hand again with airbrushing and bought a gravity feed airbrush and a compressor.  I still use the same compressor that incorporates a water trap before the air proceeds to the airbrush.  I was getting good results using Humbrol and Revell enamels and when I moved back to the UK in 2010 I began using Tamiya acrylics that also gave good results. 

 

When I moved to Cameroon last year I was unable to bring any of my enamel paints with me nor the Tamiya acrylics because they are all flammable and cannot be taken on an aeroplane.  Instead, I bought all the paints in the Humbrol and Revell ranges and brought those with me.  Initially I was mixing them with water to a semi-skimmed milk consistency but found that Humbrol had a tendency to "spit" when airbrushing and I thought they might be drying in the airbrush as I was spraying.  At this point I have three airbrushes; a gravity feed with trigger control, a gravity feed with dual action (Premiair) and an Expo bottom feed single action with bottle.  Having read/searched for advice on this forum and others for advice on what consistency to thin the paint to, I discovered during a visit to South Africa that Revell had a product that was produced for their acrylic range to add to the paint (4 parts paint to one part Aqua clean) and this claimed to increase the drying time when using acrylics.  I then read somewhere that people were advised to begin with a 50:50 mix and then add more paint or thinner to improve the performance of the paint through the airbrush.  It is difficult to measure a 4:1 ratio when you only need a small amount of paint to spray a body, chassis or kit but I have been using mustard spoons that I was able to buy locally.  In a local supermarket I found white spirit and use this to clean out the airbrush after I have used the Revell Aqua Clean and/or water.  Now I am finding that whatever mixture ratio I use that the paint comes out of the airbrush in a spray but when I spray onto a piece of scrap plastic before spraying onto the subject matter, I get a thin coat of wet paint (possibly thinned too much) and the paint looks like rain drops of paint dotted on the surface.  I have tried to alter the pressure of the spray and have moved my hand closer or further away from the item being sprayed but it seems to not make any difference.

 

I always spray indoors as it is too hot to work outdoors and have sprayed with the air conditioning blowing at 16 degrees C or without the aircon.  It makes no difference.  I have tried to spray in thin coats and allowing each to dry but I still have a dotted finish to my models.  I have contemplated buying a more upmarket airbrush such as Iwata or Neo but I am doubting whether that is the problem or not - perhaps I am doing something wrong?

 

I would be grateful for any advice and if there is something that I need to get, then providing it is not pressurised or liquid, I can order it from the UK or buy it when I next visit UK next month.  When in UK I used to use cellulose thinners after each session to clean the airbrush but that is not available here.  Unfortunately, most Cameroonians are not paid enough to have spare cash to indulge in a hobby such as model railways or plastic modelling and consequently there are no model shops and very few even what we would call toy shops.  There are also no art or craft shops.  It is looking like I might need to resort to building kits and leaving them in sections for painting when I return to the UK in a couple of year's time.  This is the first place I have ever been where the thought of pursuing modelling as a hobby might prove impossible.  Fortunately, I brought supplies of Butanone and Carr's Green flux in the container that came with me so I am able to restock on rail, chairs and sleepers to continue building track and my layout and there is an abundance of wood available.  I have even been able to restart my progress on my Friary Green layout.

 

Regards,

 

Steve

[Mick Bonwick]

It's good that your compressor has a moisture trap, have you checked whether it is empty? If there is some fluid present it may be finding it's way down the airhose. If it is the standard format you can expel the moisture by pushing up the valve at the base of the trap while it is pressurised.

 

I'm not sure of the effects of the heat that you imply is present on the paint that you are using. When you mix it before placing it in the airbrush cup does it look to be perfectly smooth and consistent in texture? Small lumps would certainly result in the effect you mention. Do you get the same result if you spray plain water onto a matt surface such as a piece of printer paper? You could try starting with plain water and then add a few drops of paint at a time, gradually, to establish the point at which the 'blobbing' starts. That might indicate whether it's a paint mixture problem.

 

I suggest that the Premiair is good enough for you not to have to 'upgrade' your airbrush to overcome this problem. I question the advisability of cleaning an airbrush with white spirit if using acrylic paints, but if it is difficult for you to get proper acrylic thinners/airbrush cleaner then I can't think of any other solution.

 

If you're visiting the UK in the near future then you could try bringing your Premair airbrush with you and giving it a thorough clean with appropriate cleaning fluid before returning, to see if it resolves the issue.

 

No immediate solution for you, but at least some things to consider and try.

[bill badger]

One thing that stood out reading your post is that you are using water based paints but cleaning the equipment with white spirit; is there a compatibility issue I wonder?

[runs as required]

OK, not Cameroon, but Ghana (similar hot humid climate and completely unaware of model railways as a hobby).

Wherever you go in Ghana there exists a flourishing wayside car repair industry - of which body repairs: metal bashing/welding/filling and finishing/spray painting are all quite distinctly separate trades but very closely interelated.

I found that at the spray painter end in Accra and Kumasi, the guys regarded themselves as artists - some even had galleries with their portraits of celeb musicians on show.

 

Have you talked to these guys about their kit, what paint materials they use (for lorry decoration artworks as well as taxi repairs) and what they use for cleaning? You may well learn something from them. Where I was based up in Ashanti, the local university art department used to work with them on the use of airbrushes.

 

dh

[Crantock]

What are you spraying onto?  Is the "raindrop" effect similar to spraying badly cleaned resin where the paint doesn't take?

 

The locally sourced retarder (ie the thing that delays the acrylic drying) might that be a factor?  I have used such retarders to a limited extent but could get from artists shops.  I am not sure how well they keep. 

 

Is it, (desperate) worth adding a drop of fairy liquid to see if destroying surface tension helps?

 

Finally, I would use a better mixing pot.  Small, thin glass ones are very available at UK shows and I use for small paint jobs.  Acrylic is easily washed out.

[lofty1966]

I certainly wouldn't be using 'white spirit' to clean the gun. It always seems to leave a surface greasy after use.

I clean my airbrush with clean pre boiled water, then acetone after using acrylic paint.

[Sam Moss]

I certainly wouldn't be using 'white spirit' to clean the gun. It always seems to leave a surface greasy after use.

I clean my airbrush with clean pre boiled water, then acetone after using acrylic paint.

I tried acetone to give a final clean and found that it ate the O rings inside the airbrush

[Torper]

As for cleaning an airbrush after using acrylic paint, there are some useful tips at http://www.britmodeller.com/forums/index.php?/topic/234921018-airbrush-cleaner-for-acrylic-paints/.  It seems that different paints react differently to different cleaners.  If the nozzle of your airbrush is clogged, or partly clogged, that could be causing the spatter effect you describe.

 

I also wonder what pressure you're spraying at.  George Dent, in his very useful book on airbrushing, suggests that the optimum situation is one where the paint flows at the lowest pressure possible.  I use about 14psi, but that's with enamels - Dent also suggest that acrylics may need a slightly higher pressure to atomize the paint compound sufficiently.  On th other hand, he also suggest that if the paint is too thick, or the air pressure insufficient, a spatter effect will again be the result.

 

DT

[lofty1966]

I tried acetone to give a final clean and found that it ate the O rings inside the airbrush

If you leave them in soak they do get affected. I blast through and wipe over to finish.

[Daddyman]

Might help in the diagnosis if you could photograph the results - in very good Cameroonian light? 

[Crantock]

If you leave them in soak they do get affected. I blast through and wipe over to finish.

I suppose it depends what brush you use but I separate the valve before any soaking. I do use white spirit as part of the process post enamels but never on acrylics. It then gets an ultrasonic bath and you can see the White spirit and gunk coming off. The valve is removed at this stage.

[6029 King Stephen]

Thank you for all the replies and advice so far. I will take a few pictures to show what is happening. Please note that I only use the white spirit to clean out any traces of paint in the airbrush (the places that cannot be dismantled. The Revell acrylic thinner is recommended for use with Revell acrylics and water is used to thin Humbrol acrylics. After using white spirit, I always rinse through by spraying with either the Revell thinner and/or water.

 

Thanks for the suggestion to ask car painters/sprayers as they might be able to point me in the right direction for spray cans that might be useful - in the same way that I would pop into Halfords when living in UK. It is interesting the number of locals who I have shown my hand built plastic and soldered pointwork who have enquired if I am an engineer - which I am not.

 

My list of items to buy when we visit the UK soon for 11 days is getter longer by the minute. A visit to the Bristol area to buy items from C&L is definitely on the cards! Before I came here, the prohibited packed items list included paint. When the packing day came, I had already given my enamels and Tamiya acrylics to my parents to look after because they had flammable markings on them, I mentioned to the guy that I now only had acrylic paints that were water based and he told me I could have packed my enamels and Tamiya paints. What they meant as prohibited paints was large tins of emulsion or gloss! Unfortunately, I was not able to add to my packed items without incurring a large fee (in excess of £200!).

 

Regards,

 

Steve