Preparing Miniatures for Painting: Mould Lines, Washing and Sub-assemblies

Preparing a miniature before you paint it takes about ten minutes and decides how good the finished model can possibly look. Primer and paint sit on top of whatever you leave behind, so a mould line you ignore now becomes a mould line under six coats later.

This guide covers the whole preparation stage: cleaning the model, removing mould lines and sprue gates, filling gaps, deciding what to leave unglued, and mounting the model so you can actually reach it with a brush.

Why does preparation matter so much?

Paint is thin. A layer of primer is a few microns; a basecoat is not much more. None of it hides geometry. A raised mould line running down a Space Marine's shoulder pad is still a raised line after you paint it — except now it catches your edge highlight and draws the eye straight to the flaw.

Worse, some preparation cannot be done later. Once a model is assembled you cannot reach the inside of a cloak or the gap behind a shoulder. Once it is primed, glue bonds are weaker, because plastic cement needs bare plastic to weld.

How do you clean a miniature before painting?

It depends on the material:

• Plastic kits from a modern injection-moulded sprue are usually clean enough to prime straight away. If the sprue feels greasy, wash it.
• Resin almost always carries mould release agent. Wash it, or primer will crawl and peel.
• Metal carries machining oils and oxidation. Wash it, and scrub with an old toothbrush.

To wash: warm water, a drop of washing-up liquid, gentle scrub with a soft brush, rinse, and leave to air dry completely. Do not use hot water on thin resin — it softens and warps.

1. Fill a bowl with warm water and add a drop of detergent.
2. Scrub each part with a soft toothbrush, paying attention to recesses.
3. Rinse under clean running water.
4. Leave on a towel to dry fully — at least a couple of hours. Trapped water under primer causes patchy adhesion.

How do you remove mould lines and sprue gates?

Two different jobs with two different tools.

Sprue gates

Cut parts off the sprue with clippers, leaving a small nub rather than cutting flush — cutting flush risks taking a chunk of the model with it. Then pare the nub back with a sharp hobby knife, drawing the blade away from you in shallow passes.

Mould lines

Mould lines are the faint ridges where the two halves of the mould met. Do not cut them. Use the back edge of a hobby knife blade, or a dedicated mould line remover, and scrape along the line at a shallow angle. The ridge comes away as fine dust. Finish with a light pass of a fine sanding stick or a piece of 600-grit paper if the surface still feels raised.

Check for lines by running a fingernail over the surface — you will feel them before you see them. The usual culprits are the tops of shoulder pads, the centre lines of weapon barrels, helmet crests, and the length of cloaks.

How do you fill gaps and seams?

Modern plastic kits fit well, but curved joins — torso halves, tank hulls, monstrous limbs — often leave a hairline seam.

• Plastic cement melts and welds plastic. Apply a little more than you need, press the parts together so a bead of softened plastic squeezes out of the join, let it cure fully, then scrape the bead flat. This is the strongest and cleanest fix, and it only works on plastic.
• Liquid green stuff or a modelling putty fills small gaps. Apply sparingly with an old brush or a sculpting tool, let it cure, then sand.
• Two-part epoxy putty handles genuinely large gaps and rebuilding.

Whatever you use, let it cure completely before priming. Uncured filler shrinks and cracks under paint.

What should you leave unglued?

This is the decision people skip, and the one that most changes the result. Painting a fully assembled model means reaching into places a brush does not fit.

Good candidates to leave off until after basecoating:

• Backpacks and cloaks — they block the entire back of a torso.
• Weapons held across the body — they hide the chest.
• Heads, if the model has a hood or high collar.
• Shields and banners, which are often the most detailed part and are far easier flat on a stick.

The trade-off is that sub-assemblies need handling and can leave a visible join. A sensible default for infantry is to build the model completely except the backpack; for a large centrepiece, break it into as many sub-assemblies as you can still keep track of.

If a kit gives you a choice of weapons and you cannot decide, magnetise it: drill both the arm and the socket, glue a small magnet into each, and swap loadouts freely. The app's Build tab lets you record a unit's wargear per cluster, including marking an option as magnetised, so what is in the box and what is on the model stay in step.

How should you mount a miniature to paint it?

Never hold the model itself. Skin oils resist paint, and a thumb on a wet basecoat undoes an evening.

Options, cheapest first:

• A wine cork or bottle cap with a blob of poster tack. Free and perfectly good.
• A painting handle — a weighted grip with a clamp or tack pad. Comfortable for long sessions and worth the money if you paint often.
• A cheap wooden dowel or an old paint pot for models already glued to their base.

Mount sub-assemblies on their own sticks so both hands stay free and nothing touches a wet surface.

Preparing a squad, not a model

The stage that ruins momentum is doing all this one model at a time. Prepare a whole unit in one sitting: clip and clean every part, scrape every mould line, glue every torso, and only then move to priming. You get into a rhythm, and the unit arrives at the primer stage together — which is what makes batch painting possible later.

For a ten-model Space Marine squad this is comfortably an evening's work in front of the television. For a Tyranid brood with lots of curved seams, budget more.

What are the most common preparation mistakes?

• Skipping mould lines because they are hard to see on bare grey plastic. They are hard to see now and obvious under paint. Feel for them.
• Cutting mould lines with the blade edge. It gouges. Scrape with the back edge.
• Gluing everything, then discovering the brush will not fit. Dry-fit first and ask where a brush needs to reach.
• Priming over uncured glue or filler. Both keep shrinking under the paint.
• Priming a resin model without washing it. Primer peels off in sheets, usually after you have painted it.

Frequently asked questions

Do I need to wash plastic Warhammer miniatures before priming?

Usually no. Modern plastic sprues are clean enough to prime straight from the box. Wash them if the plastic feels greasy or the model has been handled a lot. Always wash resin and metal.

Can I paint a miniature without removing mould lines?

You can, but the line stays visible and tends to be highlighted by shading and edge highlighting rather than hidden by them. Removing them is the single highest-value ten minutes in the whole process.

What is the best glue for plastic miniatures?

Plastic cement, not superglue. It chemically welds the plastic, so the join is as strong as the material and can be smoothed flush. Keep superglue for resin, metal, and gluing dissimilar materials.

Should I glue miniatures to their bases before painting?

Generally yes for infantry — it gives you something to hold and avoids a fiddly join later. Leave larger models off their bases if the base needs texture and detail work of its own.

How long should I wait after washing before priming?

Until it is bone dry, which realistically means a few hours. Water trapped in a recess will lift the primer above it.

What comes next

With the model cleaned, de-lined and mounted, the next step is priming — the coat that gives paint something to grip. If you are tracking a collection, this is also the point where a unit stops being a box and becomes something you can log as built.