Concrete and Beyond

TERMS

Concrete - Cement mixed with some sort of aggregate such as sand, gravel, bits of plastic, etc.
Patching concrete - Sold in smaller quantities with or without added vinyl (I prefer without), sets faster than regular concrete, is a bit finer in texture, and requires no additional aggregate
Anchoring cement - sets even faster then patching concrete, is more dense, has less aggregate and is harder when cured
Solid Expressions™ - Solid Expressions™ concrete sets in minutes, cures hard and is ready to use in about an hour, making it perfect for a myriad of uses in jewelry and other art forms. Solid Expressions™ concrete can be purchased in my online store
Pigments - You can now mix great colors with our pigment collections, so get ready to create with colorful concrete!
AddMix (also ad-mix and various other brand names) - A liquid polymer that resembles milk in color and consistency. When added to cement (or any material that needs water to activate) it increases strength by a factor of 2-5 times and hastens both setting and curing times
Setting time - The time it takes for the reaction between combined elements to finish and for the material to harden
Curing time - The time it takes for a mixed material to achieve its maximum hardness. Often the same amount of time it takes for complete drying.

MIXING

The following refers to patching cement/concrete. Other cement/concrete mixtures will vary in instructions.

Concrete should be mixed by adding the liquid to the powdered concrete. The container should be clean and free of any grease or oil (I use clear plastic glasses so I can see the bottom of the mixture to assure it is mixing thoroughly).

Add the liquid a bit at a time and incorporate thoroughly before adding more. The initial mixture will form pea-sized lumps but with the addition of a very small amount of liquid will turn to the consistency of thick yogurt. When you draw a palette knife across the top the concrete should have a wet smooth look.

Depending on the type of concrete used, you will have between 5 and 15 minutes of work time. If the mixture begins to harden, it means the catalytic reaction has begun and the addition of more liquid to prolong the pot -life will only serve to lessen the strength of the final product.

Pigments may be added at various times in the process, however, usually liquid pigments are added with the mixing liquid and dry pigments are mixed with the dry concrete before the liquid is added.

USES

Filling a form - Any existing form can be filled with the wet concrete, tamped, and allowed to cure. Heating per above is possible; however, it will always take a bit longer to dry as the moisture can only evaporate out the top surface. After the form is filled, any inclusion may be placed in the wet concrete and allowed to remain "cemented" in place. After the hardening begins texture can be carefully introduced on the concrete surface by scratching, brushing, burnishing, etc.
Casting - A simple mold may be formed using raw polymer clay, plaster, silicone, ceramic clay, sand, texture plates, alginates, etc. Concrete may also be cast into existing rigid forms as long as there are no undercuts and a release agent is used (don't use Vaseline or oil as they stain the concrete and hinder the curing process). The wet concrete is troweled into the mold and tamped from below to help air to migrate out from the top. I usually allow 2 days for the curing time before unmolding the concrete. However after a day the mold can be heated very slowly (concrete still in it) at a low (150-175 F) temp in a toaster oven or on a radiator. When removed from the mold there will still be moisture left in the concrete and again it may be placed in a heated environment at a low temp to hasten evaporation.
Covering an armature - Concrete may be applied to a myriad of armatures including wood, plastic, screen, cloth, pierced metal, panty hose and many more. The concrete should be applied in thin coats as evenly as possible. Subsequent coats may be applied to build up a surface however, the under layer should be moistened with liquid (water or additive) before application of new concrete.
Tablets - A tablet or billet can be formed by placing portions of the mixed concrete on a piece of waxed paper or the sticky side of masking tape. The specific shape of the final piece can be drawn on the paper or tape and the concrete mixture "corralled" to fit inside the drawing thus eliminating much of the final shaping after the piece has dried. If tape is used, inclusions may be stuck down (upside down) and the shape drawn around them so that when peeled up the concrete will have the inclusions precisely where you want them. The inclusions will be flush with the surface of the concrete tablet and be free of any concrete. Voids and spaces may be formed by placing any soft material on the tape and making sure it extends higher then the depth of the concrete tablet and retracting it after the curing has occurred.

FINISHING

Shaping - Concrete formed in any of the above ways may be filed, sanded, ground, buffed and polished.
Painting & Staining - Concrete can be painted with most paints and can also be tinted by sprinkling with pigments (try iron filings or instant coffee).
Varnishes - Varnishes, waxes, some finishing oils, and their variations work well but the concrete must be completely dry before application.
Cutting - Mizzy wheels, separating wheels, and diamond burrs work well on the flex shaft and finished pieces may be cut (carefully) on a lapidary saw or sanded on a belt sander.

Play Well,
Robert