Preventing Air Bubbles in Silicone Molds (Degassing & Brushing Tips)
Quick answer (TL;DR): Vacuum-degas platinum silicone at −29 in Hg for 1 min, then brush a 1 mm “face coat” onto the master before the bulk pour. This eliminates 98 % trapped bubbles even without a pressure pot.
Three-Step Bubble-Free Method
- Mix gently with a stir-stick; keep paddle submerged.
- Vacuum degas at −29 in Hg until foam collapses (≈ 1 min).
- Brush “face coat” into all undercuts; pour remaining silicone in a high thin stream.
Equipment Guide
| Tool | Size | Ideal for |
|---|---|---|
| 2-gal acrylic chamber | 2 qt mixed silicone | Small props, figurines |
| 5-gal steel chamber | 1 gal silicone | Helmet molds, large busts |
| Press-pot @ 60 psi | — | Alternative if vacuum unavailable (forces micro-bubbles smaller than 10 µm) |
Written by Edmund McCormick. • Last reviewed 19 June 2025