This article will detail all the steps for pouring cement counter tops. Although it focuses on small practice pours, all the steps are the same when pouring the final counter top.
Practice Molds for Cement Counter Tops
A small mold about 12” by 12” and 1-1/2” deep can be reused several times for practicing. After this it is possible to do some very small pours using empty plastic food containers such as sour cream or yogurt containers. These small samples can be used to experiment with pigments.
Make a small practice mold out of 3/4” melamine-covered particle board and then calculate how many cubic feet of concrete the mold will hold. To do this, multiply the width, length and depth of the mold with all measurements in feet. If the mold is 12” wide by 12” long by 1-1/2” deep, 12” becomes 1 foot and 1.5” becomes 0.125 feet (1.5 / 12). Multiplying the three numbers together gives the number of cubic feet, so 1 X 1 X 0.125 = 0.125 ft3.
The bag of concrete mix will have a chart indicating how many cubic feet the bag will yield and the amount of water required. In general, the bags range in size from 40 to 80 pounds and will provide anywhere from ½ to a full cubic foot.
Use the same mix is used for practicing as will be used in the final countertops because each brand will mix in a slightly different way and the coloration can vary widely. For the practice pours it is not necessary to use a mixer, the concrete can be mixed in a wheelbarrow with a shovel.
Preparing for the Concrete Counter Top Practice Pour
- Have a notebook handy and note the exact weight or measurement of each ingredient added.
- The water reducer will list how much is to be used per cubic foot of concrete. Measure the amount required into a measuring cup.
- The pigment package may indicate how much must be added for a given amount of concrete or it might be necessary to simply experiment. Calculate how much water will be required and add the pigment to half of this amount of water in a measuring cup.
- Calculate the amount of poly-fibers required and weigh this amount into a small container.
Pouring the Concrete
Wear a respirator and gloves when working with the concrete mix. Once the concrete is well wetted, the respirator will not be required.
- Since the whole bag of concrete mix will not be used, it is important to first roll the bag around a bit to more evenly distribute the contents. The mix will contain Portland cement, pea-sized gravel and sand as well as some additives depending on the brand.
- Slice the concrete bag open with it lying flat so that contents can be shoveled out getting an even mix of the ingredients within. Calculate how much of the bag is needed (add a few extra pounds to the calculation for spillage).
- Pour the pigmented water into a wheelbarrow then shovel the required amount of concrete mix in on top.
- For each bag of concrete mix add one shovelful of Portland cement (so ½ a shovelful for a half bag, etc.)
- Begin mixing with shovel.
- Add the water reducer.
- The mix will be very stiff – add water very gradually mixing after each addition. Do not let the mix get soupy. The mix is adequately wet when when a handful can be lifted out and still hold together but not slump too much.
- Once the mix seems to be the right consistency, shovel one third of the wet concrete into the mold. Note how much water was used.
- With gloved hands, work the concrete into the corners and edges of the mold.
- Add the poly-fibers to the remaining concrete in the wheelbarrow. Mix well.
- Put more concrete into the mold.
- Push the concrete down into the mold and keep shoveling more in until the mold is completely full. By pushing the concrete into the mold there will be fewer air bubbles trapped in the mix.
- Press the concrete down into the mold with a float then smooth the surface with the float.
- Using a straight piece of wood (the narrow edge of a 2 by 4 works well) screed off any excess concrete by moving the wood back and forth in a sawing motion as it is slid across the top edges of the mold from one side of the mold to the other (angle the leading edge of the wood up very slightly).
- It may be necessary to remove large pieces of gravel that poke out and shovel in a small amount of concrete to fill in voids that appear.
- Once the mold is full and level, begin hammering on the mold with a plastic or wooden mallet. Air bubbles will appear at the surface. Keep hammering on all sides and the bottom of the mold until bubbles are no longer appearing. Trapped air in the counter will result in a weaker counter top.
- After the concrete has set for a couple of hours, trowel the surface with a metal concrete trowel. Do not trowel to the point that puddles form.
Curing and Finishing the Concrete Countertop
The concrete will need to be cured for a couple of days before it is flipped out of its mold, ground, pinholes slurried in, polished, then sealed.