Etch Primer - Safe to use in your every day airbrush?

[6029 King Stephen]

Hi,

 

I have some Comet brass coach and chassis kits that I would like to paint.  I have a tin of etch primer that is water based and is red in colour.  I have previously sprayed this using a cheap airbrush several years ago without any detrimental effects on the airbrush.  I simply diluted it with water, in the same way as I would do for acrylic paint and then sprayed it on.

 

However, I am now own a more expensive Iwata SBS airbrush and I would like to spray this etch primer coat before applying the top coats.  I would mix the primer outside of the airbrush and pour it into a bottle that would then feed into the airbrush.  Would I just need to follow the same cleaning process that I do for acrylic paint afterwards or would it be more prudent to buy a cheap airbrush specifically for spraying the etch primer?

 

The reason I ask is that on DVD I have on airbrushing model railway locos, Ian Rathbone uses etch primer from the Precision Paints range and suggested that he uses an airbrush set aside for this task.  However, I think that the etch primer I have is not as ferocious as that marketed by Precision Paints as it is thinned with water rather than the aggressive thinner that they use (I can't remember the type of this thinner and couldn't find it whilst searching Google which was even more frustrating!).

 

Any thoughts?  I cannot get automotive aerosol primers here such as those sold in Halfords in UK, so an African solution would be preferred.

 

Regards,

 

Steve

[Mallard60022]

I was told by someone that painted coaches for part of his living, that he used a cheap and cheerful AB for this etching stuff, never his better ones. Hope that helps?

Phil

[Quarryscapes]

I was told by someone that painted coaches for part of his living, that he used a cheap and cheerful AB for this etching stuff, never his better ones. Hope that helps?

Phil

 

I would echo this, if it dries in your airbrush it will etch into your airbrush, not good on delicate tapers! The thinners is not an issue, it's the etchant. It might be wise to have a cheapy airbrush with a 0.5mm nozzle for primers. 

[Daddyman]

The DVD that you mention is the source of information I have too, and I always stuck to it, never using my airbrush for etching primer. In recent years, though, I've used Halfords U-pol aerosol on advice found on this site. However, I haven't been entirely satisfied with it. It doesn't at all pass "the finger-nail test" in my experience (i.e. whether or not you can scrape it off with your finger nail) - I've had it come off footplate edges and cab roof corners and virtually every edge.

 

I'm inclined to question the extent to which etching primer is actually necessary. In the majority of cases it may not be. At a Missenden weekend Ian Rathbone did say that by the time you've gone over a model with a fibre glass brush, you've done all the work that etching primer does anyway - that is, slightly roughening the surface. He also said that any half etched part - e.g. thin tender overlays - will be roughened sufficiently already by the etching process when they were produced. 

 

I'll be painting a scratchbuilt brass loco this weekend and I don't think I'll be using etching primer. Instead I'll got for a dunk in Casey's gun black followed by a normal primer and then topcoat. This is the method used by DLT here: http://www.rmweb.co.uk/community/index.php?/topic/2359-dlts-sr-locos-e5x-from-wills-e5-kit/ 

 

I treated some removable brake gear and a bogie with gun black a few month ago, and they've been on my workbench being shoved out of the way for that time, with no sign of wear on the finish. 

[Mallard60022]

Many years ago I was told that soaking etches in vinegar solution, after all soldering was completed and 'cleaned', helped in two ways. One was neutralising any residual flux and also just giving the surface a little 'roughness'. I have done this but I have not really compared durability in any way. I do know that Coachman swears by certain aerosol etch primers from Halfords (I believe); well, he did when describing work on his 4mm coach work.

Phil

[John Tomlinson]

I never realised there were water based etch primers, and have always used the Precision one. The proviso is that you need a higher thinners to primer mix for spraying than the manufacturer recommends, at least 2:1, otherwise the airbrush gums up.

 

My airbrush has survived numerous trials with this rather potent chemical, but I've been scrupulous to clean thoroughly and without delay after use, initially with Precision thinner then with some cellulose for good measure. An essential for success with the Precision product is cleanliness of the metal of the model, and I prewash with something like Jif, wearing latex disposable gloves not so much to protect my hands but rather keep the cleansed model from contamination with hand grease afterwards!

 

My efforts have thankfully passed the "fingernail test" with only the odd exception, and given a good base for the final paint colour. For whatever reason, the product also works well as a primer on resin, subject to the same cleaning process - a very useful feature on a substance renowned for its greasy texture.

 

John.

[K14]

Hi,

 

I have some Comet brass coach and chassis kits that I would like to paint.  I have a tin of etch primer that is water based and is red in colour.  I have previously sprayed this using a cheap airbrush several years ago without any detrimental effects on the airbrush.  I simply diluted it with water, in the same way as I would do for acrylic paint and then sprayed it on.

 

However, I am now own a more expensive Iwata SBS airbrush and I would like to spray this etch primer coat before applying the top coats.  I would mix the primer outside of the airbrush and pour it into a bottle that would then feed into the airbrush.  Would I just need to follow the same cleaning process that I do for acrylic paint afterwards or would it be more prudent to buy a cheap airbrush specifically for spraying the etch primer?

 

Any thoughts?  I cannot get automotive aerosol primers here such as those sold in Halfords in UK, so an African solution would be preferred.

 

Regards,

 

Steve

 

'Water based and red' sounds suspiciously like Hammerite Special Metals Primer. If so I don't foresee any problems spraying it provided:—

 

1 – the pigment is sufficiently finely ground to go through the nozzle

2 – you are fastidious when cleaning up, as it could dry on the needle & cause uneven flow, or worse, glue the needle & nozzle together (but you could say the same about all water-based acrylics).

 

My old Iwata HP-B & HP-C 'brushes both have stainless needles & nozzles and most paints won't stick to them - SMP is possibly the exception. I've not tried it on stainless, but it sticks like wossname to a blanket on brass, galvanise and aluminium; I don't know what's in it (the MSDS doesn't list anything nasty) but it works. When I've sprayed it, I've used an old Badger airbrush with a slightly damaged nozzle - mostly because it has jar-feed rather than cup-feed.

 

True acid-etch primers (like U-Pol Acid 8) seem to use phosphoric acid as the active ingredient & that could affect airbrush parts over time.

 

The only issue I've had with the Iwatas was spraying xylene-based paint. Sprayed OK, but the O-rings swelled up & jammed the needle fully retracted until the solvent evaporated whereupon they settled down again.