A plaster mold is a rigid negative form used for ceramics, decorative objects, prototypes, reliefs, and small sculptures.

Plaster is economical and easy to use, but it is not suitable for every shape. Models with deep undercuts or complex details may require a multi-part mold or flexible silicone.

Plan the Mold Structure

Inspect the master before mixing any material.

Choose a One-Part or Multi-Part Mold

A flat-backed or simple object may be suitable for a one-piece mold.

A three-dimensional object may require a two-part mold with a carefully planned parting line and registration keys.

Check for Undercuts

An undercut can lock a rigid plaster mold around the master.

When the shape cannot be removed safely, a flexible silicone mold with a plaster support shell may be more practical.

Prepare the Master and Mold Box

The master should be clean, stable, and properly sealed when it is made from a porous material.

Apply Sealer and Release Agent

Wood, plaster, unglazed ceramic, and other absorbent materials may require sealing.

Apply a compatible release agent in a thin, even layer so the cured mold can separate without losing detail.

Build and Seal the Box

Use sealed boards, acrylic, plastic sheet, or foam board to create a box around the master.

Leave enough space for a strong mold wall and seal all joints to prevent leakage.

Mix and Pour the Plaster

Follow the plaster manufacturer’s recommended water-to-powder ratio.

Add Plaster to Water

Measure the water first, then sprinkle the plaster gradually over the surface.

Allow the powder to absorb water before mixing gently. Aggressive mixing may introduce bubbles.

Create the Detail Layer

Brush or pour a thin first layer over the master so the plaster reaches fine textures and recessed areas.

Fill the remaining mold box slowly and tap the sides lightly to release trapped air.

Demold and Dry

Allow the plaster to develop enough strength before removing the box or master.

Separate the parts gradually and avoid forcing sharp tools between delicate surfaces.

The mold may still contain moisture after it feels hard, so let it dry evenly in a ventilated area before use.

When RTV-2 Silicone Rubber Is Better

RTV-2 Silicone rubber for Moldmaking is suitable for complex textures, curved forms, undercuts, and repeated casting.

Flexible and Detailed Reproduction

After curing, silicone can bend and peel away from the master, reducing the risk of breaking the original or the cast part.

Condensation-cure and addition-cure systems are available with different viscosities, hardness levels, working times, and dimensional stability.

Our company supplies RTV-2 silicone rubber, catalysts, thinners, primers, release agents, and related moldmaking materials.

Request an RTV-2 Moldmaking Quote

Producing molds for sculpture, prototypes, resin casting, gypsum decoration, or industrial components?

Send us the master material, mold size, target hardness, working time, casting material, and expected quantity. We will recommend suitable RTV-2 Silicone Rubber for Moldmaking and prepare a quotation.