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Sanding Gunpla: Grits, Sanding Sticks and Removing Nub Marks

How to sand Gunpla nub marks smooth: which sandpaper grits to use, sanding sticks vs sponges, the order of grits, and how to avoid scratches and white marks.

By Gundam Models editorial teamUpdated 3 min readHow we research

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Plastic parts of a Real Grade Zaku II kit still attached to their runners on a wooden table

To sand a Gunpla nub mark, flatten the leftover bump with a sanding stick or waterproof sandpaper around 400 grit, then work through finer grits up to about 1000. Bandai recommends keeping waterproof paper in that range; the higher the number, the finer the finish. Sand only the nub, keeping the stick flat.

Bandai’s build steps include sanding parts after cutting to remove rough edges for a cleaner finish. Wikipedia explains where the rough edge comes from: each part is joined to the runner by a small nub called a gate, and builders clip, carve or sand away what is left.

What you need

Plastic parts of a Real Grade Zaku II kit still attached to their runners on a wooden table
Each small tab between runner and part leaves a nub to clean up.
Tool What it does Tip
Sanding sticks Flat, rigid sanding surface Keeps edges sharp
Sanding sponges Flexible sanding pad Follows curves
Waterproof sandpaper Cut to size, wrapped on a stick Can be used wet
Hobby knife Shaves the nub before sanding Use a fresh blade

Airfix lists sanding sticks or files for smoothing seam lines and a hobby knife for cleaning up nubs among its essential tools. Bandai recommends a replaceable-blade art or design knife rather than a snap-off cutter.

Step by step

  1. Cut cleanly first. A good pair of nippers leaves a smaller nub. Cut away from the part, then trim close.
  2. Shave or sand the bump flat. Use a fresh knife blade or a coarse stick around 400 grit. Stop as soon as it is level.
  3. Move to finer grits. Go up through the numbers toward 1000 to remove the scratches the coarse grit left.
  4. Keep it flat. Sand only the nub, not the surrounding panel lines or edges.
  5. Wipe off the dust before panel lining or top coat.

Sanding sticks and sponges

Shop sanding sticks and sponges

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Avoiding common sanding mistakes

  • Rounded edges. The stick rocked. Hold it flat and use short strokes.
  • Deep scratches. The grit was too coarse for too long. Switch to finer grit sooner.
  • Lost detail. You sanded over a panel line. Sand only where the gate was.
  • A pale patch on colored plastic. Fine sanding leaves a dull spot; a matte top coat evens the surface, or a Gundam Marker in a matching color covers it.

Safety

Bandai asks builders to take care not to hurt their fingers with files, and says small children should use them with a parent. Keep sanding dust off your work table and wipe parts clean before coating.

Seams, polishing and glued kits

Nubs are not the only thing to sand. On glued plastic kits, Airfix lists sanding sticks first for smoothing seam lines where two halves meet, and putty or filler for any gap that sanding cannot close. Some Gunpla parts also show a faint line where two halves of a part join, and the same light sanding through the grits smooths it.

For a shine rather than a matte finish, builders go past 1000 grit and polish. Mr. Hobby’s tool range has a category for sanding and filing tools and polishing compounds, and a polishing cloth, for that last step. On a kit you plan to top coat in matte, polishing is not needed.

Do you need to sand every part?

No. On a first kit, sanding is optional. Many nubs sit where they will not show once the kit is assembled. Sand the ones on visible armor first, especially on light-colored parts, where a pale mark is most obvious. On a detailed Real Grade, small parts make careful sanding worth the time.

For the full tool list, see Gunpla tools, and for where sanding fits in a build, the build guide.

Frequently asked questions

What grit sandpaper is best for Gunpla?

Bandai suggests keeping a few sheets of waterproof sandpaper between 400 and 1000 grit. Start with the lower number to take a nub down, then move to the higher numbers to smooth the scratches away.

Do I need to sand Gunpla?

No, but it helps. Bandai's own build steps suggest sanding parts to remove rough edges for a cleaner finish. A small nub left after cutting is the main thing to smooth.

How do I get rid of white nub marks on Gunpla?

Sand the spot through finer grits until the scratches are gone, then cover what remains with a matte top coat or a marker in the part's color. Cutting in two steps with sharp nippers leaves less to fix.

Are sanding sticks better than sandpaper?

They are easier to control. A stick or sponge holds the paper flat, so you sand only the nub instead of rounding the part's edges. Airfix lists sanding sticks among its essential tools.

Filed under ToolsStart with Gunpla Tools: What You Need to Build Your First Kit

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