What is the best filler for plastic model seams?

Tamiya Basic Putty is excellent for general gap filling. Mr Surfacer 500 (liquid) is better for fine seam lines. For large gaps, use Milliput or epoxy putty. CA glue with accelerator works well for small gaps and is sandable.

How do I fill seam lines properly?

Apply filler along the seam line, pressing it into the gap. Let it cure fully (check the product instructions). Sand with progressively finer grits: 400, 600, then 800. Check for pinholes under primer and re-fill if needed.

How many sanding passes are needed?

For putty, epoxy and CA fillers allow about 3 passes: 400 grit to shape, 600 to smooth, then 800 or finer for the final finish. Liquid surfacer (Mr Surfacer) self-levels, so it usually needs only 2 passes. Each pass may reveal new pinholes that need re-filling — prime between passes to check your work.

Should I use liquid or putty filler?

Use liquid filler (Mr Surfacer) for fine hairline seams and surface imperfections. Use putty for wider gaps (over 0.5mm). Use epoxy putty for structural filling and reshaping. Each has its place in the modelling toolkit.

ModelCalcs

Filler Calculator — Seam Line & Gap Filling

Estimate putty or filler needed for seam lines, gaps and corrections on your plastic kit.

Number of Seams

How many separate seams or gaps you need to fill (e.g. fuselage halves, wing roots)

Avg Seam Length (mm)

Average length of each seam line to fill, in mm

Avg Gap Width (mm)

Average width of the gap or seam in mm; depth is assumed equal to the width

Filler TypePutty for medium gaps, liquid surfacer for fine seams, epoxy for large/structural fills

Kit Fit QualityBetter-fitting kits leave smaller gaps, so need less filler; older/short-run kits need more

How We Calculate This

Calculates filler volume based on seam dimensions and kit quality, with an overfill allowance for sanding.

Formula

Gap volume = Total seam length × Gap width × Gap depth (depth assumed equal to width)
Adjusted volume = Gap volume × Kit quality factor
Total needed = Adjusted volume × Overfill factor (1.5–2× for sanding waste)

The volume is reported in millilitres (1 ml = 1 cm³ = 1000 mm³). Putty, epoxy and CA fillers are sold by weight, so the pack count converts the volume to grams using a putty density of ≈1.6 g/cm³ before dividing by the tube size; liquid surfacer is counted directly in ml.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities before purchasing materials.