How to Build a Concrete Countertop
Building your own concrete counter-tops for a modern kitchen or modern bathroom may sound like a daunting project, but with patience and perseverance, you can achieve the modern, artisanal feel of concrete counters at the fraction of the cost of having them custom made by a professional.
There are a variety of ways to build a concrete counter, from pour-in-place to precast concrete methods. This process outlines the precast method, which can be done in another location, then the finished countertop slab can be brought in and installed in the final location, such as in a kitchen or over a bathroom vanity.
Step 1: Make measurements for your countertop. We started with an “easy” countertop as our first piece, one that would not require any faucet holes and would cover the smallest surface area. Measure twice, even three times. You can also make a paper or cardboard template of the area to ensure the perfect fit to the space.
Step 2: Form the mold. Our mold form, which was reused for several sections of countertop, was made using the foam rail system from Cheng Design. First measure and cut the polycarbonate to fit the exact size or template you made, then lay down on a level working surface. We set up a large working table in the backyard under a tent to protect the form from the elements.
Step 3: Mix concrete. We combined Sakrete concrete with water. Others also use an additive. Follow manufacturer directions for concrete-to-water ratio. It took us a few tries to get the right consistency. The best mix that we came up with has the consistency of cake batter – smooth and a little spongy.
Step 4: Pour concrete into mold. Pour wet concrete mix into the form. Pack the mix down with gloved hands to ensure solid coverage throughout the mold. Then trowel to make (what will become) the base smooth and level.
Step 5: Vibrate. Using a power hand sander and/or a hammer, vibrate the mold from underneath the table and the sides. You will see little air bubbles surface up to the top. The more you vibrate, the better your final outcome will be. If you rush this process, the countertop will be full of voids, which can be filled or left alone, if you don’t mind the more natural look of the voids.
Step 6: Cure concrete. Cover in plastic to ensure the concrete doesn’t dry out. You can also lay a blanket over it overnight to help retain heat. Allow concrete slab to cure at least 48 hours. We waited several days before attempting to remove the slab from the mold.
Step 7: Remove slab from mold. Carefully remove the foam rails, especially if you plan on reusing them for another mold.
If all goes well with Steps 1 – 6, you should have a well-formed concrete countertop. The polycarbonate base layer ensures a smooth, shiny finish. If you would like a more natural finish, then can skip that step.
For larger surface areas, it is recommended to lay rebar into the mold, for maximum strength.
Step 8: Finishing. There are a variety of steps to take to get to a final, finished concrete counter. If there are a lot of voids, then can be filled with Cheng Acrylic Slurry. Once you slurry, you will have to wet-polish the counter again to achieve the smooth finish. We recommend completing all the finish work and wet polishing outside, before bringing in the finished concrete countertop.
Depending on the size of the countertop, you may need to enlist the help of a few friends to help bring the countertop into its final installation place.
Step 9: Sealing and maintenance. To ensure longevity, apply a thin coat of Cheng Sealer, then Cheng Finishing Wax to protect the countertop from staining and to act as a liquid barrier.
Materials and Tools:
- Cheng Pro-Form Mold Making System provide a unique foam rail system that can be reused for each mold needed.
- Concrete Mixer
- Polycarbonate Sheets ensure the form base (which becomes the countertop) has a glossy surface
- Form Tape to make the countertop edges smooth and shiny
- Cheng knockout if installing a faucet into countertop
- Sakrete 5000 concrete
- Metal rebar, depending on the dimensions of the counter
- Cheng Acrylic Slurry to fill in voids
- Rubber Gloves
- Hammer and/or Hand Sander
Lighting and furniture resources:
Karen Nepacena loves everything mid-century modern and spends her weekends renovating and restoring a 1959 Eichler home, which she shares with her husband and two sons.