"Tips for brush on primer" Topic

If you have a small painting space and/or live in a climate where outdoor priming is often not possible, you can still get great results with brush on primer. But it takes a little know how to make the most of it. Here are a few tips I have learned.

1. Primer is not paint. It can be hard to get even coverage with light color primers. But that is okay, think of primer like the "glue" that sticks the paint to the model. As long as the surface is coated you are okay, even if it looks crummy. You can simply use your base coat paint over the primer to give you the even coverage you need.

2. Paint on Primer can bubble. Lighter colors of primers especially can form little bubbles while brush it on that will dry and leave little "hole" on the model that do not look good. You can avoid this with a few simple methods.

First, don't load up your brush with primer. Use just enough that it goes on easy, but does not run, pool or splatter.

Second, use slow, short and gentle brush strokes. This will minimize air bubbles.

Third, when painting over rough or textured areas air can get into the primer and cause bubbles. Over these areas use a gentle, shallow dabbing motion (not stabbing) this will prevent bubbles.

Fourth, it is really hard to get white and other light primers not to bubble. Do the best you can to minimize it but as you prime keep an eye out for bubbles. When you see them, you can easily get right of them by blowing on the model with quick puff, like blowing out a candle. Sometimes it might take a few puffs but will take care of any bubbles. You can do this as you go or at the end, as long as the primer is still wet. Warning! Be mindful or your workspace. Some primer might come off the model and splatter below. So, if you are working on a surface, you don't want paint on then cover it with something like a newspaper.

Last thing to consider is if you are really not happy with your brush on primer results consider switching to a darker color. Black is very forgiving with bubbles, coverage and evenness. Black primer can be used with any color scheme really, even white and can give some real depth to the model. It is also perfect for the "slap chop" method of painting.

I hope this helps and if you have any suggestion for priming with a brush let me know!

Thank you

Primer IS paint, just formulated to adhere better to the surface and produce a surface that 'normal' paints adhere to better than the unprimed surface.

There should be no difference between the colours in trapping air, that is down to the formulation of the medium and thinners, not the pigmentation.

Black often appears to cover better than white because a thin coat of white shows the underlying surface better.

A little flow improver (I dilute to about 1:20 and then just dip the tip of the brush into that) can also help the primer to flow into the details. Although it won't prevent bubbles it will reduce the problems they can cause.

Thanks. I do a little brush on myself, and everything said makes sense.

-GildasFacit

You are correct that primer and paint are not that different in chemical composition they will have a very different effect on a model. You can paint a miniature only using primers but in the vast majority cases it will not look as good as using even low-quality paint. My point is that the purpose of primer is to bond paint to the model, and one should not expect it to look as clean and even as a final paint job.

I can speak from a lot of experience that darker primers do bubble less then light primers. While I am not sure of the exact mechanism, I believe that even within the same line of paints the formulas vary from color to color. For example, in most brands yellows have a reputation for being tricky. But this is very testable. I like Vallejo primers and if you take a model and really scrub on black you will get little to no bubbles on the dry model and a rather good-looking black cover. If you carelessly scrub on white you will get a streaky bubbly mess. (But with some practice you can use white pretty quickly too).

You make a good point about thinning. I have noticed that a very thin primer does work well when it comes to "sticking" the paint on. But it won't provide the subtle effects that an opaquer coverage provides. That is not good or back it just depends on what effect you are going for. I have heard some people prime with clear varnish but I have never tried that so I cannot say how it works.

Overall brush on primer is great for new hobbyists or for hobbyists with small budgets or workspaces. But I have met too many people who tired it once and gave up on it because it didn't provide good results.

My hope with this post was to troubleshoot some of these issues and help people understand that just like airbrush or rattle can primer, technique and understanding the process can go a long way to better results.

One tip I forgot. Brush on primer can be sensitive to surfaces that are not clean. Dust and oils (either from manufacturing, shipping or from you handling the model) can sometimes cause the primer not to stick well to the model surface. I have found that with plastic and metal models (I don't have much experience with resin) simply running the parts on the spur (or the whole model if assembled or one piece) under hot water (just hot enough that you wouldn't want to wash your hands with it but not so hot that it will burn you) for about 10 to 20 seconds is sufficient depending on the water pressure. This is not always necessary, but it only takes a few minutes and can save a headache once you start.

I have had good results using white gesso.

I use flat black enamel by Humbrol as a primer for 40 years and never an issue. Years ago, I would bake the metal figures at a low temperature, now I put them under a lamp with an incandescent bulb and that would do the trick.

+1 for white gesso. Even painted on thick it doesn't clog too many details. And no problem with air bubbles if you remove the excess gesso in time (I usually collect it on the brush and apply it to the next unprimed figure… ;-)

+2 for gesso. Any decent art supply house will have it. It's a little pricey, but a bottle will last you years. Comes in white and black, and maybe gray.

Is it worth getting? I gesso…

Sorry…

Gesso behaves differently to genuine primers. It doesn't really "stick" to the figure, rather it encases it as it shrinks on drying.
I use Liquitex black gesso. It rubs off easily ahead of finished painting but once completed all's well as long as you varnish the finished figures. Also leaving the primed figure a fair few hours ahead of over-painting is good practice as it is fairly thick so dries (and shrinks) slowly.