How to Make Precast Concrete Molds

What You'll Need
Molding rubber
Casting models
Bucket or leak-proof pot
Sealing agent
Concrete release agent
Metal file
Razor blade or sharp knife
Pail for mixing

If you want to decorate the outside of your home in a manner that is consistent and aesthetic, consider making precast concrete molds. These types of molds allow you to produce a range of concrete casts—such as for steps or blocks, so that you can produce a uniform effect. You could purchase a precast concrete mold if you chose, as there are many available online and at local stores, but a cheaper alternative is to make your own. This is easily done, so long as you ensure that you follow the instructions closely.

Step 1 - Prepare the Mold

Begin by sealing all of the holes and pores in the items which you will be using for casting. You can use a caulk here, or a specialist sealing agent. Once you have added one coat, leave it to dry for about 15 minutes. Then add a second coat and let it dry for the same amount of time. This should seal off any holes or gaps, leaving only the solid object from which to cast your concrete. You should then pour a release agent over the bricks, and also over the bucket you will be using. A latex or rubber combination is the ideal agent here.

Step 2 - Make the Pattern

Place your objects into the bottom of the bucket. This will be the pattern of bricks in this mold forever, so create the best pattern that you can. You should also make sure that you leave a gap, about an inch or so, between each object in the mold, as any smaller gaps or overlaps will lead to weak areas of the mold that could tear, making the mold useless.

Step 3 - Make the Mold

Once you have arranged the objects, pour the rubber mold solution over the top. This is usually found in a mixable form, so make sure that you have a suitable container for mixing up the mold. Pour enough of the rubber in to completely cover the objects, but not too much over. Leave the rubber to dry.

Step 4 - Testing the Mold

Extract the mold from the container. It should slide free, although you may need a razor blade or sharp knife to cut out the bottom of the mold. Clean by trimming the mold. Spray your mold with the concrete releasing agent, and pour the cement over the surface. Leave it to dry, and then invert the mold slowly to release the objects. The mold should slide free of the objects, and you should be able to use it again immediately, if you need to.