How to Make Concrete Countertops
Most countertop materials are costly and difficult for the do-it-yourselfer to fabricate and install. So imagine a different kind of countertop material with the heft and solidity of expensive quartz or natural stone countertops, yet coupled with the economy of laminate. This material is concrete. Making your own concrete countertop is a fun and extremely low-cost project. The result is a sturdy, stone-like material that has a rustic-industrial look perfect for outdoor kitchens or barbecue areas.
How Concrete Countertops are Made
Concrete countertops are always molded and they are either cast facing upward or facing downward.
Concrete countertops that are cast facing upward are usually created in place, on top of the cabinets or another intended base. Much like a sidewalk or patio, the wet concrete is poured into forms, finished on top with trowels, then left to cure.
By contrast, the countertop in this project is cured also in a form, but the countertop is created upside-down. The eventual top surface of the countertop is formed by the smooth mold and thus requires very little finishing. The sides, too, are created with melamine-faced forms that unscrew after the concrete has finished curing. Junctures are filled with silicone caulk, both to prevent wet concrete and residual water from seeping out of the form and to create ready-made bevels.
At 2 inches thick, this concrete countertop is considerably heavy and will require at least two people to move it into position after curing. For these instructions, the term concrete mold bottom refers to the position of the mold during the building and molding process. However, this bottom molding area will eventually form the top of the counter after it is flipped over.
Use the Right Concrete
For a smoother countertop with better tensile strength, purchase countertop concrete mix rather than the type of fast-setting concrete intended for patios and walkways. While countertop concrete mix may cost 3 to 4 times more than the other type of concrete, it is formulated to flow better for an easier pour. This high-strength material should achieve a hardness of 5,000 pounds per square inch (psi) after about 28 days.
Cast concrete is extremely heavy, often far heavier than it appears. For the step where you remove the mold and turn the countertop over, have one or even two assistants with you. Wear gloves because the edges will be sharp.
What You'll Need
Equipment / Tools
- Vibrating tool: rubber mallet, orbital sander, or hammer drill
- Hacksaw or bolt cutter for cutting steel mesh
- Hot glue gun (optional)
- Spring clamps
- Tape measure
- Resin mixing tub, 20-gallon capacity or greater
- Garden hoe
- Orbital sander
- Sandpaper for sander: 80, 120, 220, and 320-grits
- Indelible marker
- Miter saw
- Circular saw
- Table saw
- Speed Square
- Paint roller and several roller covers
- Beveling tool: marble, ball bearing, or glue stick
- Latex gloves or similar waterproof gloves
- Caulking gun
- Straight-edge razor blade
- Particulate respirator
- Eye protection
- Hearing protection
- Shop vacuum
- Utility knife
- Masonry trowel
- Cotton rags
- Spray bottle filled with water
- Sheet plastic
- Garden hose
- Carpenter's clamps
- Disposable nitrile gloves
- Countertop concrete mix
- Melamine-faced medium-density fiberboard (MDF) panel, common thickness of 3/4-inch
- Steel reinforcing concrete mesh, 10 gauge, flush cut
- Drywall screws, 1 5/8-inch
- Concrete sealer
- Beeswax designed for sealing concrete, stone, and wood counters
- Silicone caulk, black or another dark color
- Long strips of cardboard or 1/8-inch thickness wood project panel to create a countertop template (optional)
- Release agent: mineral oil or paste wax
- Scrap piece of 2x4
- Portland cement
- Acrylic cement fortifier
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.