How do I wash these materials off my skin and work areas?

Skin Contact unless you are using a silicone or alginate expressly made for applying to the skin, you do not want these materials in contact with the skin.

Remove from the skin as soon as skin contact occurs while the material is still in it’s liquid state. Using a soft cloth, lightly wipe clean with Acetone or Mineral Spirits and then wash affected area with soap and water.

Removing Material From Inanimate Surfaces

Urethane Rubber Or Plastic because urethanes are adhesive and will bond to many surfaces, your best bet is to clean up spills while material is still in a liquid or gel state. Once cured, material is very hard to remove. 

Silicone Rubber does not stick to many surfaces. In most cases, you can let silicone rubber cure over many surfaces and then simply remove it. However, silicone will mechanically lock onto many porous surfaces (concrete, for example). Silicone will also stick to glass. In these cases, it is best to remove rubber while it is still liquid.

Castable Epoxies and Epoxy Adhesives are adhesive and will bond to many surfaces, your best bet is to clean up spills while material is still in a liquid or gel state. 

Once cured, material is very hard to remove. 

What To Use For Clean Up:

General purpose solvents such as Acetone, Mineral Spirits (Paint Thinner), Toluene and Xylene are usually effective. They are commonly available at Hardware and DIY stores. Important: Follow all safety precautions found on container when handling these and other solvents.

Disclaimer
This FAQ article is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Safety Data Sheets (SDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.