Casting an Historic Architectural Detail

The architectural details for this crest were cast and replicated using a silicone casting compound and water putty. The crest is an 85-year old historic detail located at the stately Bently Reserve in San Francisco's financial district.

This was the broken crest needing replacement.

This was an intact shield.

First, a method needed to be devised to cast a mold around an existing, unbroken, shield crest. To facilitate this, a contour guage was used to measure the wall details around an intact shield. These measurements were then used to create a form box to contain a silicone casting compound which would encase an unbroken shield.

The form was then fastened to the wall using two #10 wood screws and clear silicone. The silicone was used as a gasket to seal the form, and lessen leakage when the RTV casting compound was poured in. As evidenced in this image, a bit of seepage was still inevitable.

After curing for forty-eight hours, and being removed with a screw driver and a sharp knife, the result was a mold which was highly detailed and relatively heavy; weighing about fifteen pounds, but was still somewhat pliable. Due to the casting material's weight, the form must be mounted securely to the wall.

A simple and inexpensive "water putty" was used to cast the final product. The powder and water were mixed to a pancake batter consistency and poured into the level mold.

Hardening time for this product will vary depending on the thickness of the casting. We waited 24 hours, although the product specifies only eight hours for hardening. As an additional precaution, to prevent breakage, a piece of inexpensive nylon screen material was cast inside of the shield.

After the cast had dried, the edges were cleaned and excess material was removed. Unlike wood or porous clay, the water putty will not stain. However, it can be painted.

The final product epoxied in place.