Do you plan to build a simple concrete countertop for your kitchen? You have come to the right place. There are plenty of resources online offering detailed instructions, but if you’re looking for a beginner-friendly approach, this guide is for you. No frills or fancy designs here – just a basic rectangular countertop measuring 74 inches by 37 inches and 2 inches thick.
If you plan to do this DIY with your friend, without any previous experience, you can manage to pull this off with our step-by-step guide. So, let’s get in and explore how to work with concrete in a forgiving manner.
Step 1: Collect Your Materials, Make a Plan
The basics for making concrete worktops are simply building your mold, and pouring and finishing the concrete. There are several acceptable materials for building the form but choose cheap and easily obtainable melamine-coated particle board. You’ll need a piece larger than your desired finished dimensions, pick a 4-foot x 8-foot piece 3/4 inch thick. Other items needed are:
- Additional melamine boards for the sides of the form
- Sturdy and LEVEL sawhorses to build on (our finished top weighed around 400 lbs)
- 3/8 inch rebar for inner support
- Remesh for more inner support
- Wire for attaching the rebar and remesh to the form
- Screws for building the form (use 3-inch and 1 5/8-inch drywall screws)
- Drill (you MUST predrill the particle board to avoid splitting)
- Saw(s), circular hand saw, and/or table saw to cut the form sides.
- Silicone caulk in a colour easily seen on your Melamine (we used black)
- Concrete tools consisting of float(s) and trowel(s)
- Long screed board
- Hacksaw/bolt cutter/wire cutters for cutting your rebar, remesh, and hanging wire
- Level
- Rubbing alcohol
- Concrete (of course). Use Quikrete 5000 without additives like fibers or water reducer.
- Pigment of choice. Pick a little black so the natural colour would just darken a bit.
- Concrete mixer.
Before starting the countertop, it’s important to make a test form. They made two small forms (1 x 2 feet) with rebar and remesh. This helps to check pouring consistency, colour, and techniques. It’s also a good way to practice finishing techniques without risking mistakes on the actual countertop. Skipping this step is not recommended.
Next, plan the size and shape of the countertop on the Melamine sheet. They didn’t need templates because their concrete worktop was a simple rectangle for an island, not against a wall. When marking the guidelines, remember to consider the thickness of the boards used for the walls.
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Step 2: Build the Form
Once the countertop measurements are marked on the melamine, setting up the sides is the next step. For a simple rectangle shape, this process is straightforward. Ensure that the sides match the desired thickness, typically 2 inches. Cut the sides to the appropriate length, clamp them in position, and attach them securely to the base using 3-inch drywall screws. It’s crucial to predrill the walls to prevent splitting. Sink the screw heads low enough to avoid interference with the screed board. While countersink bits are optional, they can be used if available.
Remember to account for the additional length of the abutment. For instance, with 3/4 inch melamine, add 1.5 inches to the end boards. Alternatively, you can extend these boards further for added support, particularly for corner brace boards. To prevent bowing, especially with longer sides, use guidelines and clamps at multiple points to keep the boards straight.
Step 3: Clean and Seal the Form
With the sides prepared, the next step is to seal all inside seams using silicone caulk. Choose a colour that contrasts with melamine for better visibility.
To apply the caulk, first, tape off the insides of the walls and base using blue painter’s tape, leaving about 1/8 inch on either side of the seams. Apply the caulk along the seams, then run your finger down the line to press and smooth it out. Don’t be afraid to get a little dirty during this step!
Remove the tape promptly after applying the caulk to prevent it from drying on the tape and potentially tearing upon removal. Allow the caulk to cure for a day, then clean the inside of the form with rubbing alcohol.
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Step 4: Prepare the Inner Reinforcement
Setting the reinforcement grid is a crucial step in the process. For a 10-inch overhang from the cabinet base on three sides, adding 3/8 inch rebar around the edges is recommended for stability, especially with larger projects. Rather than bending the rebar around corners, cut each piece about 4 inches shorter than the side to maintain a 2-inch setback and prevent ghosting when the concrete cures.
Place the rebar on styrofoam blocks about an inch thick to keep them in position as they are tied off. Secure them using 1 5/8 inch drywall screws in the base, spaced approximately every 16 inches. Use sturdy wire to tie onto the rebar, twisting it several times and clipping one end. Hook the other end onto the support screws, which will be cut after pouring the concrete and pushed into the wet concrete.
To provide additional structural support and hold the rebar in place after removing the styrofoam, add remesh. Tie it off with a wire to the rebar at several points, ensuring a solid connection. If the remesh is cut where there isn’t a solid wire against the rebar, tie it off at the nearest available point.
Once the grid is fully secured, remove the styrofoam supports, and ensure the entire grid hangs in place evenly. If there is any sagging, add more ties between the rebar and remesh.
Before pouring the concrete, thoroughly clean the surface with alcohol to remove any dirt or debris. This step is essential for ensuring a smooth finished product, even with the rebar in place, as any specks of dirt can cause blemishes.
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Step 5: Pour Concrete!
Now it’s time to work with the concrete. While smaller projects can be hand-mixed in a 5-gallon bucket, for a project of this size, a concrete mixer is essential. Renting one, like we did from Home Depot, is convenient, and ensure you return it within their specified timeframe.
The concrete should be mixed to a consistency likened to “oatmeal,” although interpretations may vary. Essentially, aim for a texture that’s dry enough to reduce cracking during curing but still manageable. It’s better to have the concrete slightly wetter than too dry. Add pigment during the mixing process for colour.
It’s advisable to have at least two people when pouring. One person operates the mixer and shovels the concrete into the form, while the other(s) use their hands to push it into place. Be cautious not to apply too much pressure over the support grid. Instead, gently scoop the concrete under to ensure proper support for the remesh.
Step 6: Screed and Float the Concrete
To level out and smooth the concrete, use a long, straight board to screed across it in a sawing motion. This helps push the concrete into the form and evens everything out. When you encounter wire ties, lift the screed board over them and continue screeding. As you screed, excess concrete will be removed, revealing any low spots or holes. Use the overflow to fill in these areas and continue screeding until the surface appears uniform.
Next, cut the support wires. Follow them into the concrete, cutting them about an inch deep. Don’t worry about affecting the concrete; focus on ensuring the remaining wire doesn’t protrude or show. After cutting all the wires, fill the spaces and rescreed if needed.
Now, use a concrete float to begin finishing. Draw the float across the surface with the leading edge raised slightly to avoid cutting into the concrete. Water may come to the surface, which is normal. The concrete should not be too dry, causing the float to tear it up rather than smooth it out. Float the surface several times if necessary to achieve a relatively smooth finish.
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Step 7: Vibrate the Form to Remove Air Bubbles
To ensure a smooth and void-free countertop, it’s essential to remove air pockets while the concrete is still wet. This can be done using various methods. One simple approach is to use a rubber mallet to gently tap the sides and bottom of the form, allowing bubbles to rise to the surface. Spend time in each area to ensure all bubbles are released. As bubbles emerge, they will grow and pop, and can then be refloated to fill and smooth them.
Another method is to use a palm sander without sandpaper to vibrate the form or a large vibration machine attached to the form. The longer and more evenly the form is vibrated, the better the result. This step is crucial for achieving a smooth finished surface without voids, reducing the potential for cracking.
Consider using a professional vibrator if building another countertop. This can be attached to the form from the beginning and operated continuously during the pouring process to maintain consistent vibration.
Step 8: Trowel the Concrete to Smooth It
Once the concrete starts to set, it’s time to use a trowel. They used an aluminum rectangular trowel with gentle pressure to smooth out any lines left from floating. Even though this side will end up as the bottom of the concrete worktop, it’s important to make it as smooth as possible for a level fit on the cabinet base.
After a few hours, they could remove the sides of the form to trowel the sides if desired. For rounded edges, a rounded corner trowel can be used on the top and/or bottom. However, they left the corners sharp and kept the form sides in place for a couple of days. They reasoned that messing with the sides wouldn’t make them any smoother. Removing the sides of the forms after a couple of days of curing allows the sides to dry fully.
When removing the sides of the form, ensure all screws are removed first. The boards should start to pull away with gentle pressure at a corner. Avoid putting any prying tool on the concrete to prevent surface damage. Instead, pry against the adjacent corner board, which should provide enough room to grab the board and pull it back. If a board seems stuck, double-check for any hidden screws under spots of concrete on the form board.
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Step 9: Flip the Countertop
After 710 days of curing, the countertop needs to be flipped face up for finishing and any necessary patchwork. Given its weight of approximately 400 pounds, four individuals were required for this task. They placed cardboard against one side of the countertop and tipped it up onto its side on the cardboard. This allowed them to slide it to the other side and then gently lower it back down, now resting face up.
Step 10: Trust The Process
Hopefully, you’ve learned from our mistakes and your countertop looks perfect by now. If you followed our method exactly, you might need to patch up any cracks. The three cracks we encountered resulted from tapping the melamine too hard during air bubble removal. Otherwise, the surface looked great, drying with an almost granite-like appearance due to the black tint added during mixing (the lighter spots in the pictures are from the flash). Though concerning initially, repairing them was relatively easy, and thought it could serve as a useful learning experience for others facing similar issues.
At this stage, it would only cost around $150 to build an entirely new countertop. So, worst case scenario, you can always build another one later if this one didn’t turn out as desired. To begin the repair process, use a wire brush to go over the entire surface. This helped open up any small air pockets hiding beneath a very thin layer of concrete. Though it may seem like a step backward, it enabled the small pinholes to be filled in the next step.
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Step 11: Fill Holes or Cracks
Knowing the colour-to-concrete ratio is crucial when using tint in the mix, as it ensures consistency when mixing a slurry for repairs. Apply two slurry passes: the first made with the same Quikrete 5000, and the second with FuTung Cheng’s slurry mix. Using a trowel or putty knife, apply the slurry, allow it to dry, then sand it down to smooth it. The holes and cracks filled nicely, and while the top was smooth when finished, lack of the same “granite” look in the three large cracked areas.
Step 12: Seal and Install
The final step is applying the finish of your choice. Opt for a food-safe polyurethane.
To install the countertop, attach a sheet of 3/4 inch plywood to the top of the cabinets by screwing it into the corner braces from the inside. This setup allows for easy removal of the top later if needed. Apply a generous amount of construction adhesive to the plywood and then set the countertop onto it. Again, this is a step that requires several people for assistance. After the adhesive has dried, it’s important to wax the top for the final finish.
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Step 13: Finish It Up
Hopefully, this has inspired you to go ahead and give building your concrete countertop a try. Although the project requires some time for drying and other steps, the actual construction doesn’t take up a lot of man-hours.
Have fun with it, be creative, and explore additional techniques for adding personal touches to your countertop. Regardless of the outcome, there’s a great sense of satisfaction in knowing you built it yourself.
Are you looking for quality ready-mix concrete for your DIY project? Look no further than Pro-Mix Concrete, the UK’s largest concrete supplier of all types. Whether it’s for countertops, driveways, or any other construction needs, Ready Mix Concrete London has you covered with top-notch products and reliable service.
