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How to Build a Concrete Countertop for Exterior Structures: Part 2 - Mixing and Pouring the Concrete

Estimated Reading Time: 5 Minutes

Raw materials for concrete countertops are available at most home centers.

Here's what you'll need:

Materials
  • Concrete Countertop Mix
  • Concrete Colorant (Powdered or Liquid)
  • Metal Wire Fencing or 3/8” Rebar or Fiberglass Mesh
  • Wooden Shims
  • WD-40 or a Concrete Release Agent
  • Plastic Film
Tools
  • Level
  • Magnesium Float
  • 5-Gallon Bucket
  • Eggbeater Mixer
  • Heavy-Duty ½” Mixing Drill
  • Screed Board
  • Bolt Cutters or Grinder
  • Concrete Rub Brick (optional)
For Your Safety
  • Safety Goggles
  • Gloves
  • Dust Mask

Concrete countertops are typically made with a special concrete mix. The advantage is that it is made with the proper mixture of materials to produce an extremely durable countertop that can be finished into a smooth surface. The mix is available in bags at most home centers. The size and thickness of the countertop will determine how many bags of mix are required. You’ll also need to calculate how much colorant you will need if you plan to add color to the countertop mix.

Step 1: The forms for the four L-shaped pieces have been built and the corners have been caulked. Make sure the caulk is dry before you pour. If you have not built the forms yet, make sure to see Part 1: How to Make a Concrete Countertop.

Step 1

Step 2: Check each form with a level before you pour. If they are not level, the concrete can settle towards the low end. A simple way to raise or lower the form is to place shims along the edges.

2a      2b

Step 3: Remove any dirt and debris from the form. Spray the form with a lubricant, like WD-40. This will help the concrete release from the form once it has cured. Concrete release agents can be used as an alternative as well.

3a      3b

Pro Tip

Make sure to lay plastic down over any areas that you want to protect. Mixing concrete can be very messy.

Step 4: The countertops will need wire or rebar to reinforce the concrete. We chose to use metal wire fencing material. The advantage is that it is already set up in a grid, so you can easily cut it to fit the shape of the form. To cut it, use bolt cutters or a grinder with a cutoff wheel. Alternative materials for reinforcing are fiberglass mesh or rebar.

4a      4b

Step 5: Pre-measure the water. Fill a 5-gallon bucket with the correct amount of water for one bag of concrete mix, per the manufacturer’s instructions. If you want to add colorant, now is the time! Add the desired amount of colorant to the water. Take note of how much colorant was used for the first batch in case you must mix multiple batches. Mix the colorant in with the water with a drill and an eggbeater mixer.

5a   5b   5c

Caution

Note that you should always wear rubber gloves and safety goggles when dealing with concrete.

Step 6: Mix the concrete. Add ½ to ¾ of a bag of concrete and mix thoroughly. Finally, add the last of the bag for the final mix. If the concrete is too thick, add a little water to smooth it out. It should pour out of the bucket, but you also do not want the concrete soupy or runny.

6a   6b   6d

Step 7: Pour the concrete out of the bucket into the form. Using a magnesium float, work the concrete into the corners making sure you get full coverage, pressing it into the corners so there are no voids.

7a      7b

Step 8: Use a rubber mallet or hammer to help vibrate the concrete by hitting the sides of the form. This will help the concrete settle down into the corners and surfaces. Use a float to smooth and level out the bottom surface.

8

 Step 9: Screed the concrete with a screed board to get it level with the form.

9

 Step 10: Place the metal wire fence sections in place. Press them down until they just disappear under the surface. Use a float to smooth and level out the bottom surface.

10

 Step 11: Let the concrete cure in the forms. Once it looks dry, add water with a garden hose to slow down the curing process — this will make it stronger.

11a      11b

 Step 12: Once the concrete tops have cured (see manufacturer's instructions), you can remove them from the forms. It is best to have a few people help lift and flip the form over. Carefully lay the form upside down and then gently nudge and wiggle the form to remove the concrete countertop. If it does not release, you can take the form apart by unscrewing the sides from the bottom.

12a      12b

Step 13: Set the sections in place to check the fit. Once you are satisfied, look at the corners and edges. If they seem too sharp or irregular, you can go over them with a concrete rub brick to round them over and smooth them out.

13

Now the four L-shaped concrete countertop sections are done! To see how to stain and seal the tops to protect them from dirt, stains, and weather, click on Part 3: Staining and Sealing.

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