How to Make Concrete Precast Molds

When attempting to remodel outdoor areas of the house you may have need of concrete decoratives, such as finished bricks or cobblestones for walkways. But finding something really unique in home and garden stores is difficult and expensive. There is another option. You can make your own concrete mold and use it to produce as many castings as you like for your outdoor projects. This guide will explain how to create and use molds specifically designed for concrete materials.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Pourable mold rubber PMC 790
• Items to be cast (Bricks or Stone)
• Leak proof container
• Sealing Agent
• Release Agent
• Concrete release agent
• Concrete
• Mixing pail
• Razor blade
• Steel File
• Concrete Scraper

Making Precast Brick Molds

1. Seal the pores of the bricks or stones to be cast in a mold. Use a store bought sealing agent, shellac, or paste wax. Use at least two coats and let them dry fifteen minutes between coats. Set them aside to dry.

2. Use the release agent on the bricks and the container. They can be found in hardware stores, usually in a spray can. What you specifically want is an agent that acts on latex and rubber polysulfate.

3. Use the sealing agent again on the inside of the leak proof container. A rubbermaid container will work well, though cardboard can be substituted if the mold is very small.

4. Place the bricks or stones in the desired pattern at the bottom of the leak proof container. This is how your bricks will always look when you use this mold, so make sure they are placed exactly as you want them. Try to leave at least an inch of space between each brick so there will be no weak spots in the ensuing mold

5. Take your pourable rubber and mix it up in an expendable jug or pale. It will typically come in the form of a liquid agent and a powdered agent which must be combined before it can solidify.

6. Pour the liquid rubber into the container, taking care not to splash it over the bricks themselves. Pour in just enough to bring the liquid rubber up to be flush with the top of the bricks. Allow to dry for the rest of the day.

7. When the rubber is hardened, remove it from the container. If you coated the walls of the container sufficiently it should slide free. Twist the rubber mold to pop the bricks free. Use your razor blade to cut out the bottom of the mold so that only the dividing lines between where the bricks went remains. Clean it up by shaving the interior edges of the mold free of any loose shreds of rubber.

Using The Precast Mold

8. Place the mold down firmly into the earth where you wish to cast your brick or stone walkway.

9. Spray or apply your water-based concrete releasing agent to the inside of the mold. It is necessary in order to remove the concrete items you cast from the mold.

10. Mix up your cement and pour it into the holes of the mold. Tap it from side to side to free any air bubbles trapped in the cement that would weaken the bricks.

11. Use the concrete scraper to wipe the top of the mold clean of errant cement and smooth the tops of the bricks. Allow the cement to dry for a full day.

12. Press down on each of the bricks to unseat them from the mold and pull the mold up at the same time. The mold should come free and leave the bricks in the exact configuration you desired.

Tips & Warnings

• Most mixable rubbers smell terrible and can cause coughing fits, wear a respirator or learn to hold your breath when mixing them.

Resources

• A site that sells good mold agents