Reinforcing Design-Cast 66 with Aggregates

Aggregates such as sand, fine stones, crushed glass, perlite, Styrofoam^®, or almost any inert granular material, may be added to DESIGN-CAST in amounts up to 2 parts of aggregate (by volume) for each part of dry mix.

Reasons for using Aggregates

• An aggregate is used when you want a special appearance or texture of the piece. The incorporation of crushed stone such as marble or granite will produce a piece with a more stone-like appearance and feel.
• In order to attain the best properties (i.e. strength, freedom from cracks, maximum exterior durability) you should incorporate one or more aggregates in a thick piece, or in one which is not uniformly reinforced by fiberglass. In this case you should use at least one part of aggregate for each part of DC-66 dry mix.
• If you want to fill a hollow piece with a heavy or light weight material to make it solid, you can use a heavy or light weight aggregate added to the DESIGN-CAST mix as a compatible fill material. Suitable lightweight aggregates are perlite, or Styrofoam^® particles.
• Aggregates can also be used to reduce the material cost in large or thick castings.

Types of Aggregates to use

The aggregate should be granular or coarse in size, and free from very fine or pulverized materials. Typically all the material should be coarser than about 80 mesh.

In general, don't use an aggregate in the same layer of DESIGN-CAST mix which contains fiberglass. An exception is fiberglass mesh, which is compatible with smaller-size aggregates. You can, however, use an aggregate in a surface coat which is backed up by one or more coats of fiberglass-reinforced DESIGN-CAST 66.

Don't use a filler like vermiculite (which has a high water absorption) or one which otherwise makes the DESIGN-CAST mix too thick or too stiff to work with.

Recommended Aggregates

• Coarse sand or fine stones
• Crushed marble, quartz, granite or other dense rock (avoid using pulverized marble or limestone, or marble dust, since these materials will thicken the DESIGN-CAST mixes excessively)
• Ceramic or porcelain grog, screened to remove material finer than 80 mesh size
• LIGHTWEIGHT: perlite or Styrofoam^® particles
• METALLIC: powdered steel, bronze, brass, and other copper alloys
  CAUTION: DO NOT USE ALUMINUM POWDER OR FLAKE! ALUMINUM REACTS WITH DESIGN-CAST MIXES!
• TRANSPARENT: crushed glass, glass beads—colored or uncolored

Mixing and Incorporating Aggregates

Following the mixing procedure, mix up a batch of DESIGN-CAST 66 using dry mix, polymer, water (and pigment, if desired).

Then stir in the aggregate manually—or mechanically at a slow speed—until uniformly mixed. YOU CAN ADD AS MUCH AGGREGATE AS WILL STILL KEEP THE MIX WORKABLE, and will not cause excessive air entrapment.

Apply the aggregated mix to the armature or surface of the piece, working out any trapped air while modeling.

Finally, proceed with curing and finishing as described later.

Exposure of Aggregates

After the aggregated mix hardens, the aggregate will usually remain hidden below a thin surface layer of DESIGN-CAST, unless steps are taken to expose it. Aggregate color and texture can be exposed by one of the following methods:

• Grind or sand the surface with an abrasive grit
• Sand-blast the surface until you reach the desired depth of exposure of aggregate
• Brush on a 1:1 mixture of muriatic acid and water, and allow the acid to etch the surface for a few minutes
  CAUTION: MURIATIC ACID IS HAZARDOUS. FOLLOW SUPPLIERS PROPER HANDLING INSTRUCTIONS WHEN USING THIS ACID!

When using any of the methods above, scrub down and rinse the surface with water afterward in order to remove the particles loosened by the treatment. Finally, coat the surface with a clear, weatherproof sealer, such as DESIGN-CAST AA-6 or AA-7, or Krylon^® spray acrylic lacquer.