Is it safe to bake my Ultracal 30 mold in my kitchen oven?

Luis Cederborg

Sorry if this is a dumb question, but I am new to working with latex masks and ultracal
I have read that Ultracal 30 molds need to be baked in the oven to release excess water in them before attempting to do a latex dwell for a mask
But haven't found any info on whether it's safe to do it in the same oven I use for food. Is it absolutely necessary to use an oven? Or could I maybe achieve the result with a heat gun or any other method in case it's not safe to use kitchen oven?

Chris Ellerby

Ultracal and Hydrocal molds do work better for latex dwelling when they are dry.

When working with a new material, I recommend reading its MSDS/SDS: https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/sds/usg-ultracal-30-gypsum-cement-sds-en-52000000118.pdf

The safety concerns with Ultracal are generally around the powdered state, with inhalation and eye exposure. 

From https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/usg-ultracal-30-southard-submittal-en-IG1939.pdf

All casts should be dried as quickly as is safely possible after manufacture so that maximum physical properties can develop. Dry to a constant weight.

The best drying rooms or ovens provide 1) uniform and rapid circulation (minimum of 15-30 fps (4.6-9.1 mps)) of air with no “dead spots” having little or no air movement, 2) equal temperatures throughout the entire area, and 3) provisions for exhausting a portion of the air while replacing it with fresh air. High humidity surrounding the drying room or oven inhibits drying efficiency because the air pulled into the room is incapable of picking up much moisture from the molds.

The maximum temperature at which USG Ultracal 30 Gypsum Cement molds are safe from calcination is 120 °F (49 °C). With substantial free water in the mold, a higher drying temperature can be used initially without difficulty. As drying progresses, the temperature must be reduced to prevent calcination. Before removing molds from the dryer, the temperature should approach that of the area around the dryer to prevent thermal shock.

I know someone on the RPF forums recommended baking at 200 °F for 8 hours, but that goes against the documentation above.  The concern is that calcination might make the mold less durable. 

Ultracal molds will naturally dry out over time.  If you have a fresh mold that you want to use quickly, you can leave it out in the sun to help evaporate the moisture out of it.  Keeping it in a warm room with a fan blowing on it can help.  A heat gun would work, however, I would avoid heating it too much or too quickly as expanding steam can cause the mold to fracture, and too much heat can cause calcination.

Otherwise, you can dwell the latex longer to adjust for the water content in the mold.
It is generally a best practice to never use your home oven for anything other than food, that way you never have to worry.

/Chris

Tom Luca

There are no stupid questions in this life, the only stupid question is the question not asked. But, generally speaking it is not good to use your Mother's oven or kitchen. You can build ovens to bake foam latex in you know. I know because I'm building one. Well, I'm in the process of it. It's huge, a walk-in oven with plenty of room enough for 4 creature/monster suits, and dozens of leftovers.