How to Make Concrete Countertops

1. Create a Countertop Template

   If your concrete countertop needs to conform to the dimensions of base cabinets and walls, you can achieve precise results by starting with a template. Cut long, thin strips of cardboard or wood project panel and lay them on the base cabinets' perimeter. Be sure to account for any desired overhang. When you have the exact dimensions of your eventual countertop, carefully glue the strips together with the hot glue gun. After about 5 minutes, gently remove the template.
   

2. Scribe the Bottom of the Concrete Mold

   Lay the countertop template on top of the melamine side of the MDF sheet. If one of the long sides of the template is perfectly straight (as is typical), you can use this to your advantage by running the long side of the template along the factory-cut long side of the melamine board. Clamp the template with spring clamps so that it does not move. Scribe the outer dimensions of the template with the marker.
   

3. Cut the Concrete Mold Bottom

   With the circular saw, cut the concrete mold along the lines that you scribed earlier. Since these cuts must be perfectly straight, use a saw guide if needed.
   

4. Cut the Sidewalls for the Concrete Mold

   Because you will be pouring concrete into the mold, it needs to be formed like a container. You will be building sidewalls out of strips of melamine MDF board. With your table saw, rip the wood into strips that are 2 3/4 inches wide and a few inches longer than each side of the countertop to allow you to cut the sidewalls down to size.
   

5. Build the Sidewalls for the Concrete Mold

   For better access when drilling, it is helpful to place the concrete mold bottom on a table. Lay the sidewalls against the sides of the bottom mold. The sidewalls must be resting on the table, with the melamine surfaces facing inward. Mark cut points on the sidewalls with the indelible marker.

   Remove the sidewall boards and cut them to size at a 90-degree angle with the miter saw. If you have any sections of the mold that jut inward such as for sink cutouts or side protrusions, you will need to make miter cuts (45-degree angles) for a better concrete pour. If you do not do this, a small section of MDF will be exposed to concrete.

   After cutting, attach the sidewalls to the sides of the concrete mold bottom with 1 5/8-inch drywall screws. Check for square with the Speed Square. Hold the sidewalls in place with the carpenter's clamps as you drill.
   

6. Add a Bevel With a Silicone Bead

   Injecting silicone to all of the 90-degree joints on the inside of the mold serves two purposes: It results in a bevel that eases the edges after the form is released and prevents concrete from seeping through seams in the mold.

   Put on your latex gloves. Inject a bead of silicone caulk to all 90-degree joints. Then switch to your preferred beveling tool. Any item with a rounded end, such as a marble, ball bearing, or even the end of a glue stick, can be used to provide a consistently smooth bead as you draw it along the length of the caulk.

   Two parallel tracks will form on both sides of the bead. Do not wipe these off.
   

7. Remove the Excess Silicone

   After the silicone has fully cured, use a loose blade from your utility knife to peel off the two tracks of the excess bead. Once you get under the bead with the blade, you should be able to pull the rest off by hand.
   

8. Cut the Reinforcing Mesh

   With the hacksaw or bolt cutter, cut the steel mesh so that it is the size of the countertop mold, minus about 2 inches on each side.
   

9. Add the Release Agent

   Though melamine is a slick material, it is helpful to add a release agent to the entire inside of the mold to make it easier to remove the mold. Clean the inside of the mold with the shop vacuum. With the cotton rags, rub down the surface with a very thin coating of paste wax or mineral oil.
   

10. Pour the Concrete Into the Mold

    Wearing latex gloves and using the garden hoe, mix the concrete with water in the mixing tub according to the manufacturer's instructions. It is helpful to have an assistant during this step since concrete sets fairly quickly. Pour the concrete into the mold, spreading the concrete evenly by hand. As the concrete builds up, occasionally press it down with the paint roller. Put on nitrile gloves to protect your skin from the concrete and press your hands into the mix to force it down to the bottom of the mold and the sides.
    

11. Add the Steel Mesh

    When the concrete is 1-inch high, smooth it down with the roller, then add the steel mesh, lightly embedding it.
    

12. Vibrate the Concrete

    To eliminate voids, the concrete should be vibrated from time to time. The easiest way to do this is to tap the sidewalls with a rubber mallet. Some do-it-yourselfers prefer to press a vibrating electric tool such as an orbital sander or a hammer drill against the sidewalls. If possible, vibrate the bottom of the form, as well.
    

13. Screed the Concrete

    Continue mixing and pouring concrete over the top of the mesh until the concrete exceeds the top of the mold. Vibrate the mold one final time, then screed off the excess concrete with the scrap piece of 2x4 board. Trowel the concrete smooth with the masonry trowel. Even though this will form the bottom of the countertop, you will want it to be relatively smooth so that it will properly mount.
    

14. Let the Concrete Cure

    Cover the concrete countertop with sheet plastic. Occasionally apply a light spray mist to the concrete with the spray bottle and cover again. Leave for a minimum of 18 hours before de-molding. Preferably, let the concrete cure for 3 full days to reach 2,500 psi hardness.
    

15. Remove the Mold

    With the cordless drill, remove the screws holding the sidewalls in place. Pull the sidewalls away gingerly. Sand down the surface with 120 or 80-grit paper to make it relatively smooth. With an assistant, flip the countertop over. Carefully remove the bottom mold, exposing the top of the countertop.
    

16. Soften the Countertop Edges

    Though you created bevels in the countertop, inevitably some unexpected sharp edges will result. Buff these down with the orbital sander fitted with 220-grit sandpaper.
    

17. Finish the Top of the Countertop

    Sand the top of the countertop with 220-grit paper. If voids appear, fill with a mix of Portland cement and acrylic fortifier. Let the slurry filler dry, then sand again with 320-grit sandpaper.
    

18. Seal the Countertop

    Clean the countertop with the shop vacuum. Using cotton rags, apply four coats of sealer. Let each coat fully dry before applying the next coat. After the sealer has dried, apply countertop wax.
    

Tips for Making Concrete Countertops

• Whenever working with concrete, time is of the essence. After the water has met the concrete mix, it will begin to harden, so you should work quickly but efficiently.
• The mold sidewalls will receive great pressure from the concrete mix. Fasten them very securely.
• Make sure that the mold is resting on a perfectly flat, level place.
• After the pour, keeping the concrete lightly moist is key to preventing cracks.

When to Call a Professional

This concrete countertop project is intended to be a rustic one for areas such as patios, home offices, or dry bars. Fabricating true kitchen-grade concrete countertops is a more involved process. For this, consult a professional concrete technician who can fabricate and seal a countertop for you.