Mix and Pour the Concrete
Watch video of this step.
For our 12-square-foot countertop, we needed three 60-pound bags of ready-mix concrete. Add water to the concrete and mix with a shovel per the manufacturer's instructions.
If you want to add color to the countertop, now’s the time to add pigment to the mix. Pigment additives come in powder or liquid. Liquid pigments are easy to measure and mix, especially with small concrete batches like this one. But don’t forget to account for the amount of water in the pigment when measuring the water for the concrete. Controlling the amount of water added to the concrete mix is critical to producing consistent color. Refer to the manufacturer's guidelines.
Mixing the concrete correctly is critical to its strength and durability. When it achieves the texture of peanut butter it’s time to add it to the mold. Remember that the concrete at the bottom of mold will become the top of the concrete slab.
Using a small spade or bucket, pour the concrete into the mold, pressing and compacting it as you fill the mold to a depth of about 1 inch or halfway full.
Set the galvanized wire into the concrete, taking care that it does not touch the edges of the mold. The wire will keep the concrete from cracking as it dries and it will also add strength.
Continue to fill the mold on top of the wire, tamping the concrete with a trowel, as you go along to ensure it is well-packed. Your objective is to slightly overfill the mold. The level of concrete will drop slightly in the mold as it settles.
Smooth the concrete surface with a hand trowel. This will draw the aggregates to the top.
To settle the concrete, use an orbital sander without sandpaper against the sides of the mold. The vibrations will help bring air bubbles in the concrete up to the surface.
When finished, gently cover the countertop with a sheet of plastic or damp burlap to protect it from dust and dirt.
Let the concrete cure at least a week—the more it cures, the stronger it gets.