The hand-fill method for making a GFA is similar to the injection method, though the injection hole and vent hole are not necessary.
1. Release the mold sections the same way you would if you were going to inject the silicone. Make sure the release is completely dried before the next step.
2. Brush or stipple a thin coat of mixed silicone encapsulator on both halves of the mold, positive and negative. You might want to experiment with thixotropic agents if you find the encapsulator is too runny, even when stippled on thinly. You shouldn’t need to, however.
3. Mix up the silicone gel and allow it to de-air; when the encapsulator has dried (but not cured), pour the gel into the mold negative. If you are going to color the gel intrinsically, now is the time to do it!
4. Fit the positive carefully into the negative and clamp the two halves together securely, then oven cure it at 200°F (93°C). Again, the recommended length of time is 2 to 3 hours for a 1-inch (2.5 cm) Ultracal or other gypsum mold. The remaining three steps are exactly the same.
The oven curing is not essential. If you do not have access to an oven or hot box, the silicone will cure at room temperature; it will simply take longer. The results will be identical.