This guide gives a basic step-by-step flow for anyone casting polyurethane for the first time. The goal is a bubble-free, homogeneous and repeatable part.
1. Preparation and safety
Ventilate the area, wear gloves and goggles. Read the material's Technical Data Sheet (TDS) and Safety Data Sheet (SDS). Bring A and B to room temperature.
2. Prepare the mold
Make sure the mold is clean and dry. Apply a release agent if needed. Place the mold on a stable, level surface before casting.
3. Set the correct mix ratio
Polyurethane systems work at a fixed A:B ratio (e.g. 1:1 or 2:1). A wrong ratio leads to sticky, soft or uncured parts. Hand mixing requires precise weighing; a static-mix dispensing system delivers the ratio automatically and consistently.
4. Mix
Aim for a homogeneous blend. If hand mixing, scrape the cup and mix for at least 30–60 seconds — which introduces air. With a static-nozzle system the mix happens mechanically inside the nozzle, producing fewer bubbles.
5. Pour
Pour before the pot life ends, in a thin, continuous stream from the lowest point of the mold so air can escape upward. Vibrate the mold lightly or apply vacuum if possible.
6. Cure and demold
Wait the manufacturer's cure time. Demolding early causes deformation. After removing the part, trim any flash.
Common problems
- Bubbles: Pouring too fast/high, over-mixing. Fix: slow pour, static mixing, vacuum.
- Sticky surface: Wrong ratio or incomplete mix. Fix: check ratio and mixing.
- Incomplete fill: Pot life ended too soon. Fix: work faster or choose a longer pot-life material.
For consistent results, moving from hand mixing to a compact dispensing and casting system like Flovv noticeably reduces waste, bubbles and ratio errors.