How to Process Silicone for Mold Making

1. Measure Components

Weigh silicone according to the mix ratio. Be sure to measure the base material first in a clean and dry mixing bucket. Use a digital scale (accurate to ± 0.1 gm) when measuring for best results.

2. Mix Thoroughly

Add activator to the base material and stir thoroughly with a paint stick or a paddle drill bit, making sure that the sides and bottom of the mixing container are scraped and well mixed.

3. Vacuum Chamber

Place mixed silicone in a vacuum chamber to draw out added air bubbles from the mixing step described above. Be sure to use a mixing bucket tall enough to prevent the silicone from rising over the side. Note: The silicone will rise 3-5 times its original volume until the air is expelled from the material; and the material falls back to its original volume. Continue degassing for an additional 5 minutes. Release the pressure back into the vacuum chamber gradually.

4. Pour

Carefully pour the silicone into a corner of the mold box, trying to fill from the bottom up. Do not pour on top of the master to avoid breaking off the gate it is glued to, or trapping air in de-tailed surfaces. Fill ¾” over the master.

5. Allow to Cure

Allow the silicone to cure overnight or until the TDS instructs. (Tip: Two ways to minimize air bubbles in the mold: Put poured mold into a vacuum chamber for 5-10 minutes and allow any trapped air to be expelled. And/or put mold into a pressure tank at 40-60 psi during the entire curing process.)

6. De-mold

Deconstruct the mold box and remove the silicone mold. Once the master part is carefully removed from the mold, give the silicone mold a slight post cure in an oven at 120° F for one hour before casting a first part. (Tip: Some molds need to be cut open along a parting line. Use a narrow xacto knife with a sharp blade to make cuts that will act as locking features when putting the mold back together.)

7. Finished Product

Clean out any flash, blow off the surface of the mold with compressed air, and put the mold back together. Use packing tape, rubber bands, or wood with screws, ensuring not to over compress the sides of the mold. The mold is now ready for polyurethane casting!