THREE: MIXING THE CONCRETE FOR PRECAST CONCRETE COUNTERTOPS

• Concrete Mixers are rated by cubic foot capacity with most popular sizes being 5, 9 and 12 cubic feet. It’s important to note that these capacities are the total volume of the drum, not the amount of material you can mix.
• Here are some general rules we follow when sizing concrete batches for the mixer on hand:
  •    5 cf mixer yields 2.5 cf of mix.
  •    9 cf mixer yields 5-6 cf of mix.
  •    12 cf mixer yields 8-9 cf of mix.
• Combine all the dry ingredients in the mixer and cover the mouth of the mixer with a trash bag secured by a bungee cord.
• Run the mixer for 5-10 minutes to thoroughly blend all the pigments, additives and concrete before the addition of water.

Step 2 – Add the Water

• Measure and set aside any water or other liquid ingredients while the dry components are blending.
• If you’re using an admixture like CX Precast Concrete Countertop Pro-Formula, follow the instructions for the admixture, NOT the instructions on the bag of concrete mix.
• Add just 3/4 of the recommended water to the dry blend and mix.
• Since each bag of concrete has different water requirements, we don’t add all the required water at once. You can always add more water if the mix is too dry… but you can’t take water out.

Step 3 – Get the Right Mix Consistency

• Run the mixer for 5 minutes after addition of initial water (3/4 of total).
• Slowly add the remaining water a little at a time to avoid adding too much. Pay careful attention to the viscosity of the mix.
• The ideal mix will not be runny or watery. A simple test that we use is to scoop a handful of concrete out of the mixer and hold it in our hand. The concrete shouldn’t flow between our fingers until we gently vibrate our hand. If the concrete doesn’t flow through your fingers when you shake/vibrate it, then you should probably add more water.