Problem with non-drying paint

John Palmer
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Problem with non-drying paint

Postby John Palmer » Thu Mar 31, 2016 11:34 am

Having a bit of a problem with some paintwork, and would appreciate thoughts on where I am going wrong.

I have a completed Johnson Bogie Tank ready to receive its black livery, together with a D&S 6 wheel fish van in same state of completion which I am now using as a guinea pig so far as application of paint is concerned. The problem can be seen in the attached picture of the fish van: the coat of supposedly dull black enamel applied to the underframe has partly failed to dry 18 to 24 hours after being applied by airbrush. Note that in some areas, however, the paint has dried to a full matt finish. Judging by the manufacturer’s dab of paint on the tin lid, the finish may, indeed, be too matt. Precision drew a distinction between a dull finish and a matt finish.
011.JPG

The fish van has been primed with Phoenix Precision 2-part etch primer which has been allowed to dry for about 36 hours prior to application of the black to the underframe. The black is Precision Paints Dull Black B52. It is, admittedly, quite an elderly tin, but has been throroughly mixed with an electrically powered paddle and appears to have suffered no deterioration through age. For airbrushing, it was mixed with white spirit thinners to the consistency of milk before application with the result illustrated.

I suspected that I might have obtained a dry, fully matt finish on part of the fish van’s underframe by airbrushing at a distance at which the paint mist is almost dry as it hits the target surface. However, my second shot attached shows a scrap test piece of unprimed brass where the paint was airbrushed on at distances of 6” and 1” (as marked). In both cases the finish is fully matt rather than dull, and when sprayed at 1” was visibly wet as it hit. This suggests to me that the distance from which I was airbrushing was not affecting the finish.
013.JPG

I can live with a uniformly matt rather than dull finish, but a paint coat that doesn’t dry fully is a disaster, and has led to the Bogie Tank having to be stripped back to bare metal once already. I really don’t want to have to do that again, so would be grateful for views on how to avoid a repeat of this. Ditch the tin of Dull Black? Or is it possible that this is a problem of the paint reacting with the etch primer? Or was the 36 hour drying/etching allowance for the primer not enough?

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Tim V
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Re: Problem with non-drying paint

Postby Tim V » Thu Mar 31, 2016 12:08 pm

I have never had success with "etch" primer. I prefer rattle can primer.
Tim V
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allanferguson
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Re: Problem with non-drying paint

Postby allanferguson » Thu Mar 31, 2016 3:54 pm

I would be suspicious of the "two part" primer. Very hard to ensure the mix is complete and consistent, I think.

Allan F

mickeym
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Re: Problem with non-drying paint

Postby mickeym » Thu Mar 31, 2016 10:25 pm

I would just spray it with some random (choose to taste) enamel paint....
Don't go over thinking about it works sometimes.

I used to paint vintage R Royce chassis when I was 19ish, we used [i]hammerite mainly - Its not what you use, it is how you use it ;)[/i]

John Palmer
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Re: Problem with non-drying paint

Postby John Palmer » Thu Mar 31, 2016 11:43 pm

Thanks for the replies.

My second attempt to prime the upperworks of this Bogie Tank with self etch have produced a lovely thin coat beneath which the detail remains crisp. I don’t want to forego that benefit if my only error has been to allow insufficient time for the primer to do its work.

Phoenix Precision say that “more paint finishes are ruined by the application of paint over Etch Primer that is still drying than almost anything else”. Although I had allowed more than the minimum of 24 hours for the primer to dry I think it’s possible that the solvents it contains had still not evaporated by the time I applied the top coat of black shown on the fish van, so I think I may try waiting several more days before another attempt at a top coat on the engine.

Somewhere I’ve read that it is a bad idea to use different manufacturers as the source of paint coats and varnish coats on any given model, but unless someone tells me that it’s definitely a Bad Idea to apply paint coats from different makers I may well try a coat of Humbrol enamel, along the lines mickeym has suggested.

Troubles never come singly, and this evening I managed to fracture the plastic handle on my cherished Badger 200, just at the point where it is threaded to screw into the main body of the airbrush. I know I can source a replacement from Shesto if needed, but because I’m a tightwad I have instead turned a brass internal sleeve to form a solid mounting for both of the two broken elements of the handle. Think the plastic of the handle was probably getting a bit age-embrittled, so the reinforcement provided by the sleeve should provide me with a substantially more robust airbrush than before.

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stevecarr
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Re: Problem with non-drying paint

Postby stevecarr » Fri Apr 01, 2016 8:52 am

Morning John

For what its worth I've been using Halfords etching primer with some success.

I also use a hair dryer to start the drying process, just on a medium heat and only for a couple of minutes. I made add the dryer is surplus to requirements and not Jacqui's current machine!

The frames are Gibsons, for some Midland tank or other, and are shown in the primer coatimg.

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stevecarr
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Re: Problem with non-drying paint

Postby stevecarr » Fri Apr 01, 2016 8:59 am

IMG_1563.JPG


Sorry John - forgot to press buttom. Story of life?

dal-t
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Re: Problem with non-drying paint

Postby dal-t » Fri Apr 01, 2016 9:12 am

I think you've found your problem in one, insufficient drying time. Never mind what it says on the tin/packet, for brass bodywork, where good adhesion of the primer is essential, I personally wait at least a week (and often much longer) before attempting to lay down top coat. As for mixing brands of paint, I think this is good 'fallback' advice, but can be safely ignored when appropriate by those with a greater understanding of what they are doing (of course, even as a fallback it's not infallible, many manufacturers have both enamel and acrylic within their ranges, often with names that aren't totally self-explanatory, so using one on another could cause problems). Just a warning on the Humbrol enamel, make sure it is a 'pot' you're happy with, there have been many problems reported with recent batches, particularly those that carry a Union flag denoting production moved back from China (I've got several such tins of Ferrari Red that refuse to dry under any conditions). Finally, good save with the Badger. I did something similar, but using plastic tube and solvent for the mend, when my ancient 350 suffered a similar failure a long time ago. It is still holding up well (albeit relegated now to 'light duties' like spraying track colour on ballast) after 20 years or more, so yours should be good for at least a half-century!

PS Just seen stevecarr's posting, and I certainly endorse the hairdryer advice. My wife won't have one anywhere near her head, but I actually have two for modelling purposes (one's in the basement and the other's in the attic).
David L-T

FCA
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Re: Problem with non-drying paint

Postby FCA » Fri Apr 01, 2016 9:46 am

Did you "do what it says on the tin" when mixing the etch primer with its thinners?
I ask because as opposed to what it says on the tin (1:1), Ian Rathbone recommends two parts etching thinners, one part cellulose thinners to one part primer. I'm not sure if or how this would affect the top coat though.

Richard

John Palmer
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Re: Problem with non-drying paint

Postby John Palmer » Fri Apr 01, 2016 11:40 am

Right, in view of the David’s post I’m definitely going to postpone putting on a top coat and make quite sure that primer coat is fully dry. The primer still has a distinct chemical ‘niff’ and I’m guessing this may be because the etching process is still active.

Advice on Humbrol paint duly noted and stored!

Richard, I don’t know whether the thinner component of the 2-part primer is cellulose based (doesn’t have the peardop smell of the cellulose thinners I usually encounter), but I do know from Phoenix’ web page on etch primers that it contains the acid required for the etching process. In answer to your question, yes I did follow the instructions and mix 1:1 on the first application of the primer. This resulted in the appearance of paint cobwebs on the model, the airbrush, and other unwanted places. A websearch against ‘etch primer’ and ‘cobweb’ revealed that a higher ratio of thinner to paint is required to avoid this effect, so I can confirm the wisdom of Ian Rathbone’s advice.

Having stripped the model back to bare metal, cleaned and degreased, etc, I applied a further coat of primer with something close to a 60:40 ratio of thinner to paint. Not a hint of cobwebbing, and the satisfactory thin coating of primer I described earlier. The moral: disregard the Phoenix instructions and up the proportion of thinner.

Good morning Steve! Yes, I too have learned the value of waving a hair dryer at a model, and I am amazed at how quickly it can warm up metalwork. The danger of playing a dryer over a wet coat is one of blowing particles of dust, hair, etc onto it. It may be better to use a dryer for pre-warming of the surface to be painted.

I assume those frames are for 58072 (or is it 3?) and I am interested to note what looks like a bore in one of the stretchers for mounting a central pivot for the bogie. Here’s a shot of my engine’s chassis, on which you can see that my bogie is now mounted on a swing arm pivotted on a stretcher that also acts as an attachment point for the ashpan. Immediately behind the trailing driver you can see the length of spring steel wire I mounted at the front of the swing arm. This wire works in a slot in a piece of brass mounted on a frame stretcher so as to impart side control to the swing arm.
002.JPG

This is a split-everything chassis - including the ashpan! To achieve pick up from the bogie wheels, I made the bogie itself entirely from metal, but insulated the axle bearings from the bogie frames by mounting them in delrin bushes. Wire leads are taken from the axle bearings to small busbars glued to the bogie sideframes, and from there current is transferred to the mainframes via fine multistrand wire terminated in miniature plugs I turned from brass to facilitate dismounting of the bogie from the engine. The locomotive is collecting current from all eight wheels in a most satsisfactory manner.

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stevecarr
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Re: Problem with non-drying paint

Postby stevecarr » Fri Apr 01, 2016 12:48 pm

Hello John

Your chassis looks very good indeed. If mine is 1/2 as good I'll be happy!

My chassis in the 'photo is an earlier incarnation - shown purely to illustrate the etch primer finish - it has been dismantled because of further considerations by yours truly. I'll keep you posted.

The notion of pre warming with the hair dryer is worthy of consideration so next time out I'll give it a go. Of course how warm is warm?

See you soon.


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