How do you control expansion and pour volume?

Understanding Expansion Rates

Each polyurethane resin, such as Polyform, has a set expansion rate determined by its chemical formulation. This means the amount that the mixture expands after mixing and pouring is predictable if the correct proportions are used. Always refer to the product datasheet for the specific expansion factor to estimate your final volume before starting your pour.

Measuring and Mixing for Precision

For reliable results, use precise scales to measure both resin parts according to the manufacturer’s guidelines. For instance, a typical polyurethane system may use a 90:100 ratio by weight for parts A and B. Mix gently but thoroughly to avoid introducing air, which could affect both expansion and surface quality. Pour the prepared mixture into your mould immediately after mixing, as polyurethane resins often have a short working time.

Practical Pouring Advice

• Fill moulds only to the recommended level indicated in the product instructions or fill guide—the resin’s expansion will fill the rest.
• Pour slowly to minimise the risk of spills caused by rapid expansion.
• If working with intricate or delicate shapes, ensure mould walls are robust enough to contain the pressure of the expanding resin.