How do I brush paint a model without leaving brush marks?

Brush marks are a paint-consistency problem before they are a technique problem. The thinning, the loading and the one-direction rule that give a brushed finish an airbrush cannot be told from.

Difficulty: intermediate
Time: 40 min
Read: 5 min

Short answer

Thin the paint until it flows — roughly the consistency of single cream — and put on two or three thin coats rather than one covering coat. Load the brush properly and remove the excess, lay the paint down in one direction, and stop going back over an area once it starts to tack. Let each coat dry completely before the next.

Almost everyone who says they cannot brush paint is using paint straight from the pot. Unthinned model acrylic is formulated thick enough to cover in one coat, and a coat thick enough to cover in one pass is thick enough to hold the marks of the bristles as it dries. Thin it and the same brush leaves nothing.

What you'll need

A good synthetic or sable brush in a size larger than you think
Thinner or flow improver
A palette — a wet palette if you have one (optional)
Kitchen roll for unloading the brush

Step by step

Use a bigger brush than the area suggests.A larger brush holds more paint and keeps a fine point if it is a good one. Painting a panel with a tiny detail brush means constant reloading, and every reload is a new wet edge and a new mark.
Thin the paint on a palette, never in the pot.A drop or two of thinner or flow improver stirred into a small pool. Aim for something that flows off the brush rather than sitting on it. Two thin coats always cover better than one thick one.
Load the brush properly and then unload it.Dip about a third of the bristle length, then draw the brush once across the edge of the palette or a piece of kitchen roll. A brush overloaded to the ferrule floods the recesses and dries as a ridge at the edge of every stroke.
Lay the paint down, do not scrub it in.Touch the brush to the surface and draw it in one direction with light pressure, letting the paint flow off. Pressing the bristles flat is what puts the ridges in.
Work in one direction and keep a wet edge.Start at one edge and work across, each stroke slightly overlapping the last while it is still wet. Acrylic skins in seconds, and a stroke into paint that has started to set drags the skin into a ridge.
Stop when it starts to tack.The strongest instinct is to go back and even it out. That is exactly when marks appear. Leave it, let it dry, and correct on the next coat, which will hide almost everything.
Let each coat dry fully.Fully, not touch dry. A second coat over a half-dry first lifts and drags the first. On a warm day acrylic is workable again in minutes; in a cold room it is much longer.
Use a retarder or a wet palette for large flat areas.Both extend the working time, which is the entire difficulty with flat panels. A wet palette also keeps a mix at a constant consistency for a whole session rather than thickening as you go.

Tips

Look after the brush and it will do half the work: rinse before the paint dries, never let paint reach the ferrule, reshape the tip and store it upright or flat, never bristles down.
Bright reds, yellows and oranges are transparent by nature and need a light base coat rather than more coats. Painting them over grey primer is the usual reason people conclude their brushwork is poor.
For a big flat surface, thin more and add a fourth coat. There is no thinning level at which a single coat covers evenly on a brush.

Common mistakes

Painting straight from the pot — Undiluted model paint is thick enough to record the bristle marks as it dries, and it fills the moulded detail. Thinning is not optional for a brushed finish, it is the technique.
Going back over a coat that has begun to set — The surface has skinned while the paint underneath is still wet. Brushing over it tears the skin and drags it into ridges, which is far more visible than the unevenness you were fixing.
Using a worn or splayed brush for flat areas — A brush that has lost its point deposits paint unevenly across its width, which prints as parallel lines. Keep the tired brushes for drybrushing and glue.

If it doesn't work

Visible parallel ridges in the dried paint

Cause: Paint too thick, or too much pressure on the brush — Fix: Sand very lightly with a fine abrasive once fully cured, then re-coat with more thinned paint and lighter strokes.

The first coat looks streaky and patchy

Cause: It is meant to. A thin first coat never covers — Fix: Let it dry completely and apply the second. Judging coverage from a first thin coat leads people to thicken the paint, which causes the marks.

Paint has pooled in the recesses and lost the detail

Cause: Brush overloaded — Fix: Unload the brush on kitchen roll before each stroke, and if it has already pooled, let it dry and strip that area rather than adding more on top.

A hard ridge where two areas meet

Cause: The wet edge dried before the next stroke reached it — Fix: Work in smaller sections, or add retarder to extend the open time. Sand the ridge back when cured before re-coating.

Brush strokes show only on flat panels, not on detail

Cause: Normal — texture hides marks, flat surfaces show everything — Fix: Thin more for the flat areas specifically, and consider a rattle can or airbrush for large uninterrupted panels.

Questions people ask

Can brush painting genuinely look as good as spraying?

On detailed surfaces, yes, and often better because you control exactly where the paint goes. On a large uninterrupted flat panel a spray finish is more even, and that is the one place the difference is honestly visible.

Which brushes are worth the money?

One or two good ones beat a set of twenty. A quality synthetic or a sable that holds a point and springs back does more for your finish than any technique, and it lasts years if paint never reaches the ferrule.

Should I use a wet palette?

For miniatures and any session over about half an hour, yes. It keeps the paint at a constant consistency instead of thickening between strokes, which is one of the invisible causes of uneven brushwork.