What is the best base material for diorama groundwork?

Extruded polystyrene foam (XPS) is the most popular choice. It is lightweight, easy to carve with a hot wire cutter or craft knife, and takes paint well when sealed with PVA. Modroc plaster bandage over a foam core gives the best combination of strength and sculptability.

How thick should diorama groundwork be?

For flat terrain, 20-30mm is sufficient. Hilly terrain needs 40-60mm at the highest point. Rocky cliffs might need 80mm or more. Start with a foam core built up in layers, then shape with plaster or filler on top.

What texture paste works best for groundwork?

Premixed lightweight filler (Polyfilla or similar) is excellent for general groundwork. Mix in fine sand for texture. For specific effects, Vallejo and AK Interactive make purpose-made terrain pastes. Tile grout mixed with PVA also works well for rocky surfaces.

How do I seal XPS foam before painting?

Apply 2-3 coats of PVA glue diluted 50:50 with water. This seals the foam and prevents spray paint solvents from melting it. Alternatively, cover the foam entirely with plaster bandage or texture paste before painting. Never spray directly onto unsealed XPS.

Groundwork Calculator — Free Diorama Tool

How We Calculate This

The calculator estimates material quantities from diorama base dimensions, terrain complexity and construction method.

Terrain complexity multipliers

Flat: 1.0x
Gentle hills: 1.3x
Rocky/cliff: 1.8x
Urban ruins: 1.5x
Trench: 1.6x

XPS foam sheets are assumed 600×450×30mm; the foam-core weight is the solid-block volume × foam density (≈0.033 g/cm³, i.e. 33 kg/m³ for standard XPS) before carving. Plaster bandage uses 2 layers (3 for rocky/trench terrain); the roll count assumes a standard Modroc roll of 8cm × 3m = 2400 cm² per layer.

Coverage estimates

Consumable quantities use practical bench rules of thumb (no manufacturer publishes exact coverage), all adjustable under Advanced Options: texture paste ≈3 cm²/ml, PVA ≈1 ml per 10 cm², and fine sand/grit ≈0.5 g/cm² of textured area. Treat them as a starting shopping estimate and tune to your own application thickness.

Frequently Asked Questions

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Last updated: March 2026

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