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EPOXY BONDED SAND - EPOXY BONDED STONE

How to make imitation sandstone, permanent sand sculptures and sand carvings.


Medallion cast in imitation sandstone

You can easily make cast products that have the look of something carved from sandstone. Or you can make a permanent "sand castle" type sculpture.

MATERIALS NEEDED

- You need a rubber mold to form the cast product. If the product is fairly shallow, such as a plaque, you can use a thick-walled silicone rubber or polyurethane rubber mold. If the product is deep or if the mold is a thin latex rubber mold, you will probably need to make a rigid backup mold around the rubber mold. You will be pressing the epoxy sand mixture into your mold, and an unsupported rubber mold will distort out of shape.

Products made with this technique will reproduce the mold very well - you can use a mold that has fine details and your cast product should come out nicely.

- You should use a release agent on your rubber mold to prevent the epoxy from sticking, and to prolong the mold's life. You can use special spray-on release agents supplied by your epoxy supplier, or you can wipe a thin coat of petroleum jelly onto your mold.

- You need ordinary builders sand or "play sand", such as is used for making concrete and mortar. If you want your cast product to have a very even-grained look, you should run the sand through a sieve and remove all the small pebbles.

- You need clear epoxy. If you are testing the technique or making small products, you can use the type of clear epoxy sold in small bottles in hardware stores and craft stores as an adhesive. If you will be making many products, it will be less expensive to buy clear epoxy casting resin from a plastic resin supplier.

- You need mixing sticks and containers. With epoxy, you can use wood sticks, waxed paper cups, and many types of throwaway plastic tubs from food products.

- If your mold is deep, you will need a stick for tamping and packing the sand mix into the mold. You can use a wooden dowel or other stick. For shallow molds, you can use your fingers (protected by rubber gloves).

- Remember to wear protective gloves and eyewear when working with epoxy, and work outside or in a well-ventilated area.

- Epoxy does not cure at low temperatures. It is best if you can work in an area at about 70-80 F.

PRELIMINARY EXERCISE

In your kitchen, get some fresh, moist brown sugar and play around with it a bit. Stir it, pack it in a measuring cup, and press it with your fingers. The way the brown sugar looks and acts is almost exactly the way the epoxy bonded sand will look and act as you pack it in your mold. Notice that the brown sugar has no visible water, but it is moist, sticks to itself, and can be packed tightly in a cup.

CASTING TECHNIQUE

1) Prepare your mold with release agent if necessary. Put enough dry sand to fill your mold in a mixing container. Put on gloves and safety glasses.

2) Mix a very small amount of epoxy compared to the amount of sand you need to fill your mold. For each cup of sand, you will need less than one fluid ounce of epoxy.

3) Add part of the mixed epoxy to the sand. Stir the sand and epoxy very thoroughly with a mixing stick. The grains of sand will quickly start to moisten and clump together. Mentally compare the mixture to the brown sugar you played with earlier. If the sand seems dry, crumbly, and doesn't stick to itself very well, add more epoxy. If the sand seems wet or there is any visible liquid, add more sand. When you get the mix just right, make note of how much epoxy you used, so you can duplicate your results the next time you make this casting.

4) When the sand mix seems just like brown sugar, add about a 1 inch layer of it to your mold. Use a wooden dowel or other stick, and tamp the sand down. Add another layer of sand, and tamp it down on top of the first layer. Continue until the mold is full. To make a smooth surface on the final layer of sand, you can press and smooth the sand with a piece of waxed paper.

5) Let the casting cure until hard, and remove it from the mold.

SOLUTIONS FOR PROBLEMS

Cast product has a smooth or glassy surface where it contacted the mold, instead of a grainy, sandy surface.

Use less epoxy in the casting mix. You should not see any liquid epoxy in the mix - it should be just moist.

Finished casting crumbly, not strong.

Use more epoxy in the casting mix.

Casting never cures, or cures like taffy (not rock hard)

Can be the result of low temperatures. Try to work in an area of at least 70-80 F.

Can be the result of old resin. Use fresh resin.

Can be the result of damp sand. Make sure the sand is dry. You can put it in an oven for 15 minutes or so at the lowest setting if there is any doubt.

Cast product does not reproduce all the detail of the mold.

Tamp the mix into the mold with more force. Pay special attention to undercut areas.

Sieve the sand before use, so all the grains are the same size.

OTHER THINGS TO TRY

You can use the same general technique with small pea gravel, crushed glass, or even sawdust. Just be aware that the larger the size of the filler material, the less it will be able to reproduce the details in your mold.

To use sawdust, remove all the very fine dust with a sieve, and use only the larger shavings and chips. The sawdust will absorb resin, so you need to use more resin for the same size casting than you would if using sand. The finished product will look similar to something carved or pressed from particle board.

You can use colored sand to make your products, or add colored sand to certain areas as an accent, or alternate layers of different-colored sand. Experiment!

You can use polyester resin instead of epoxy resin, but you need to work in a very well-ventilated area. Your cast products may not be as strong as epoxy either.


Download a PDF source list

Includes 26 suppliers of all mold making and casting materials mentioned in ALL the demonstrations on this web site, including silicone rubber, polyurethane rubber, latex rubber, polyurethane plastic, epoxy resin, polyester resin, molding clay, foam board, release agents, pottery plaster, Hydrocal, metal powders, other plastic resin fillers, and gelatin molding compound. With company names, addresses, phone numbers, and web sites. Downloads to your computer as a PDF file.



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