"Does primer need an undercoat?" Topic

Perhaps a silly question.

Should I give my metal models a spray of grey undercoat before applying an acrylic black primer or can the primer go straight onto bare metal? I am assuming that it can, seeing it seems to be a primer in its own right.

By definition a primer cannot have an undercoat; primer means first coat.

If the paint is specified as a primer then it should be designed to go on the bare material.

An undercoat MAY act as a primer (the purpose of which is to improve adhesion) or it may just be used as a colour base for the top coat or to improve coverage of later coats.

I use white craft paint as a primer on metal & plastic figures without problem so no you don't need an undercoat.

I normally do a spray of grey acrylic primer bought from the car shop on my models, but the weather is not really suitable for that this time of year, so this is why I am now trying a paint-on primer. It just didn't feel right applying a "paint" to bare metal but it is clearly sold as a primer, so here we go!

Thanks.

Bigger question for a before primer is do figures need to be cleaned? Have at times but mostly not. Either way for having oldest since 1981 never had any issue yet.

Talc powder is used as a flow enhancer and release agent in metal castings. So most people do wash the figures after cleaning any flash or mold lines to remove the talc and any oil residue from handling the figures during clean-up. It used to be also recommended to soak the figures, after clean-up, in a mild acidic bath(vinegar) to lightly etch the metal surface to increase primer adhesion.

A good over-coating is likely a better measure for preserving the paint. I use an application of The Dip, which is polyurethane + stain. The polyurethane forms a tough skin over the top of the paint, bonded to the paint, itself. Even if the paint breaks away from the surface of the miniature, it can't go anywhere.

I paint plastic Army Men figures for gaming. Nothing sticks to that plastic for very long… Nothing. I've had the paint break away from the surface of the plastic (I only paint the parts which differ from the color of the plastic, so their uniforms are typically not painted, but they are coated with polyurethane-stain). When the polyurethane breaks away from the surface of the plastic, it typically flexes a bit, but returns to press against the plastic, even though it is not bonded to the plastic anymore. Their paint, and the polyurethane, hug the plastic's surface closely, unless I forcefully rub it to tear the polyurethane. I've had Army Men figures last for more than a decade, without repainting, using this technique.

This will work on resin and metal miniatures as well. If you don't like The Dip, use a coating of clear polyurethane, instead. You will likely want a matte clear coat, to dull the polyurethane, but that is easy. Cheers!

I have never washed professionally cast metal figures and have never had any problems.
Nor have I ever washed plastic.

I do wash resin.

One of the alleged causes of "lead rot" on old lead figures is storage in an acidic environment. Wood boxes have enough acetic acid in their enclosed environment to attack the lead and cause runaway lead rot.
For that reason, I would NOT recommend "etching" a figure in vinegar.

If I ever see anyone recommending washing 3D printed figures it will just be time to go bang my head on a desk.

Like Winston I only wash resin. Never had a problem.

As Gildas said, by definition a PRIMER is designed to be a first coat and is chemically different than normal paint. So technically if you just use "paint" as your first coat you are not priming at all.

That said, I do not prime. I use a coat of black on figures for shading effect. On 6mm tanks I don't prime or undercoat at all. I just put on my first color on the bare metal.

Wash in vinegar? Lead acetate is soluble in water. Make your own lead rot.

Same reaction with any metal. Vinegar is a weak acid but you're still looking for trouble.

Metal + acid = salt + hydrogen

Really not a smart move. Never washed a metal casting. Car primer spray has worked for decades.

I've always washed all mine with dish detergent, and an old soft toothbrush. It can't hurt- besides, it removes bits of cut-away metal or plastic*, and grease from my fingers as I might grip them during drilling or conversions.

* -And there's ALWAYS bits of cut-away plastic clinging on!

I wash the figures in warm soapy water and take care to rinse them afterwards as the soap leaves a residue. The castings come out of the wash process rather cleaner than they went in, so on that basis I think it's worth doing as something is clearly being removed.

I then degrease the casting before using an acid etch primer designed for painting cars. Anybody who paints cars will tell you how important degreasing is to ensure that the etch bonds with the clean metal. The etch primer is designed is activate as it dries and chemically bonds with the metal.

fyi, Another alternative is zenithal priming. Prime entirely in black, then briefly prime in a lighter color from a highlight position. : powerfisted.com/?p=199

Like Winston I have been working in plastics for over 50 years, metals for around 45, never washed, I prime metals but not plastics. I have never had a problem. I do wash resins though. However, if you put a coat of something underneath a primer you are defeating the whole purpose of a primer.

Re: Vinegar …

Since it came up. A couple of days ago I watched a YouTube tutorial about some model railroad scenery. A stain to replicate simple weathered wood was made by immersing some fine steel wool in white vinegar and leaving it for three days, with a loose lid for gases to escape. It worked beautifully. You just have to throw away the useless steel wool.

Vinegar rinse? I did use this technique with a 54mm white metal figure when it was recommended in a magazine (Scale Modeler, I think). Dipped in vinegar briefly, then rinsed in hot water. 50 years on, the painted figure has shown no signs of deterioration. I haven't used it after since untreated figures retained paint equally well.

I have followed Timmo UK's advice with regard to metal minis.

Metal and resin should always be washed in at least warm, soapy water and then thoroughly dried off. Mold release can affect the adhesion of a primer. I also use rubber gloves while drying and assembling to keep finger grease off the minis.

Some people also wash plastic. Personally I have not found it necessary with plastics. But that doesn't mean it's a bad thing if you do it. Finger grease can and will get on plastics during assembly. But I have found that not washing plastic seems to not affect the paint job's durability as long as a primer and a thick protective coat are both used.

Now as far as an undercoat – acid etch primer is probably the best for metals. However, I hve found that what you coat your minis. with after painting is the key to protecting paint jobs from chipping and wearing off.

I've used the Army Painter primers, GW's sprays, Walmart spray primers, Rustoleum, Krylon. From my experience they all function pretty well as an undercoat for plastics, resins, and metals.

But after painting I use Mod Podge sealer which is far superior to modeling varnishes. After the Mod Podge I apply a coat of brush-on matte varnish to get rid of the Mod Podge sheen.

You can achieve close to the same thing by using two coats of gloss modeling vsrnish. But Mod Podge will do in one coat what what it takes at least several coats of varnish to do.

As long as you're using a spray paint that says it's designed to stick to plastic or metal (or both) it should work. For resins I find that all the primers I use on plastics work equally well on resins.

Sorry for a bit of a derail, but:

Wash in vinegar? Lead acetate is soluble in water. Make your own lead rot.

Are any metal figures still made with lead? Most of the stuff now available is non lead white metal, is it not?

But after painting I use Mod Podge sealer which is far superior to modeling varnishes.

Why is that? Modelling varnishes are acrylics and Mod Podge is PVA. Wouldn't an acrylic "crust" be harder? I use Mod Podge to seal my terrain as the spray can propellants eat away any exposed foam.

Thanks for any input.

@Bowman,

The Mod Podge is a thicker coat more than anything. Not saying that an acrylic varnish doesn't provide a hard coat. But because it's simply a physically thicker coat. Probably the ultimate thing to do is to do a coat of Mod Podge and then a coat of varnish over that as opposed to several coats of varnishes.

I'm not a chemist but it seems to me that Mod Podge puts a better layer over the mini. than a varnish does.

But on the other hand it could very well be that several coats of varnish do equal a Mod Podge coat.

I'm really going on my experience with it and how it feels when I run my finger over the mini. to test its texture.