Often, we find that a repair or restoration involves replacing a piece of missing plastic. The pictures on the left are of a 60 year old piece of radio gear with just such a problem.

After trying several materials, we stumbled upon a product called Plast-Aid (www.plast-aid.com), typically used for repairing pool and spa PVC breaks.

Plast-Aid comes in two parts, a white powder and a clear liquid. Once mixed together, it turns into a liquid about the consistency and color of Karo syrup that can be poured into a mould to create a casting. In about ten minutes, the liquid turns to a putty that can be shaped. In about another ten minutes, the putty hardens into a solid plastic that can be filed and drilled.

The subject of the repair on the left was a National Radio Company audio filter. Its case was made of Bakelite. As you can see, it was missing one entire corner. To replicate the missing corner, we used a good corner to create a mould that would be used to repair the missing corner. The mould was made by pouring melted candle wax into the undamaged corner. Once the wax hardened, we removed it from the good corner and used painter's tape to fasten it to the missing corner. A small batch of Plast-Aid was mixed, and a few drops of black acrylic paint were added to color match it to the case's original black Bakelite.

After the Plast-Aid turned from its liquid to its putty state, we shaped the rounded corner to the correct radius. In about 10 minutes, the repaired corner was hard enough for final sanding and painting.

Click on any picture to enlarge it
The missing corner.
Wax mould hardening in a good corner.
The mould, now moved to the missing corner.
The completed restoration, after painting and reassembly.