Here I’ve applied the first, really thin coat of rubber. It flows like honey and gets somewhat messy. This captures all the detail.

I am using Mold Max 30 high-tear-strength silicone rubber from Smooth On Corp. Used with the thickening agent Thi-Vex, this rubber has the most wonderful creamy texture, and it will hold onto a surface upside down.

Many more photos after the jump.

Second coat of rubber, slightly thicker.

Third coat of rubber

For the third coat, I’ve added a small amount of polypropylene fiber to double the strength. You can find this at concrete suppliers; it’s often called “stealth fiber.” I’ve added a bit of color to each batch so I do not lose track of where the last batch was.

Pre-cast registration lines

I press pre-cast registration lines into the last coat. Rubber is pretty floppy and has no structural integrity. These lines prevent the mold rubber from collapsing away from the hard outer shell.

Trimmed edges

I have trimmed the edges nicely to prepare them for the outer shell. Once again, I’m using the steel pin method (used on the armature) to make the hard outer shell pieces. I make several pieces per side to prevent the final casting from locking into the mold.

Mold tape wall with bolts and T-nuts

Another tape wall — but this time with a new addition: T-nuts and 2 1/2 inch bolts to hold the side pieces to one another. It is a very efficient method, so there’s no need for rubber bands, strap clamps, or wing nuts.

Closeup of the T-nut held perpendicular to the surface.

I make sure the T-nuts are perpendicular to the surface. Otherwise the bolts can become crooked and impossible to remove.

(Continued in the next post…)