Artificial Stone Manufacturing With Silicone Part 1: Making Your Mold

Making the Mold with Silicone for Artificial Stone Manufacturing

For some things, you can't beat the look and feel of natural stone. But the right stone can get expensive -- not to mention heavy. Artificial stone manufactured with silicone molds that is suitable for exterior veneers, elements of interior decor, paving blocks for walkways, tiles, steps, fencing and more is lighter than natural stone and costs much less for most applications.

Plus, making stone for specific uses ensures that it will fit properly and provide a uniform look. You can copy nearly any look you want and make it happen with molded artificial stone.

Most types of artificial stone are made from concrete combined with types of crushed rock. By incorporating different substrates, you can achieve nearly any look you want. Concrete is also inexpensive and can hold up to inclement weather, so it's a popular material to use in making artificial stone.

Creating the right artificial stone starts with making the right mold. With a durable mold, you can reproduce nearly any look you want and create identical stones, tiles or sections for installation. Different materials can be used to create your mold; silicone is popular, though latex and polyurethane can also be used.

Three main methods are used to create a mold for making artificial stone.

Block Mold

Making a block mold is fastest and easiest, but it also uses more silicone or molding material than other methods.

1. Start with a model section of stone or tile that you plan to re-create. This prototype is what you'll use to make the mold that all other sections or tiles will look like.
2. Build a molding box around that model. Some people use plywood or other scrap wood to make their molding boxes, but you can use any type of existing box that your prototype fits into, even cardboard, as long as it is sealed. 
3. Mix up your molding material according to the manufacturer's instructions. Your goal is to eliminate all the air bubbles that you can in the material, because once the mold is set, the air bubbles will be weak points. As well, bubbles around your prototype can keep your mold from being perfect and create bumps on the finished stone.
4. Place your prototype into the molding box and pour in your silicone mold making material. Start pouring into a corner of the mold so that it fills up and flows gently across your prototype, as this will reduce bubbles that get trapped. Pour a thin stream and lift your container as you empty it to get all the larger bubbles to pop.
5. Fill with enough silicone to completely cover your prototype, then give it at least another half-inch. This will be thick enough to make a durable mold that won't bend out of shape when you later fill it with concrete. 
6. Once the molding material is cured, take apart your molding box -- cardboard can simply be ripped away.

Brush-on Skin Mold with Backing

This method uses much less silicone but can be more time consuming. It also reduces the bubbles that may be in the silicone and gives you a more perfect mold.

1. Place your prototype on a piece of wood or cardboard on a stable, solid surface. 
2. Use a small paintbrush (size depends on the size of your prototype, but for artificial stone that doesn't have too much detail, a 1/2-inch to 3/4-inch brush should work well) to paint on a layer of silicone. Make sure you do this quickly so the material does not start to cure before you're done. The brush will help prevent bubbles from staying in the silicone. 
3. Add a stabilizer to your silicone and paint on a second, thicker layer until you have at least a half-inch of silicone surrounding your prototype. 
4. Apply a rigid backing material to make your mold solid and easily reusable. Rigid foam is a popular choice because it is lightweight and not too expensive. If you use foam, you'll need to construct a box around your mold to give the foam something to expand into. Plaster is another option if you don't want to use a bounding box.
5. Let the backing material cure and gently remove it. Then remove the silicone mold. Place the mold back into the backing material shell to give added support when you pour into your mold.

Cast-in Skin Mold with Backing

This method is perhaps the most complex but uses the least amount of silicone.

1. Place your prototype in a temporary box and apply a thin layer of clay or wax over the surface. This layer will eventually be removed to create a gap that the silicone will fill.
2. Fill the space over your spacer material with your support -- foam, plaster or another backing. 
3. Once the backing is cured, remove the box and gently pull the support away. You should be able to peel away the clay spacer.
4. Use a small-diameter drill bit appropriate for your backing material to create cast and vent holes in the support.
5. Place the support back over the prototype. You should have a gap between the two and holes that you can pour your silicone into to fill that gap.
6. Use a funnel to carefully pour silicone into the mold. Pour slowly and with a thin thread to remove bubbles.
7. After the silicone has cured, remove the support. Carefully remove your silicone mold from the prototype and place it back into the support, ready for your mold material.

Whichever method you choose, be sure to let your silicone or other mold material cure for the recommended amount of time. Generally, this can take between 18 and 24 hours, but some types of mold-making silicone have catalysts added that improve cure time.

Gluegun.com carries top of the line Wacker silicones that are widely used in the artificial stone manufacturing industry. Contact us for samples or to receive more information on how our silicone products can help improve your stone manufacturing process.