Pour-in-Place Concrete Countertops

Our NeoMix Original System Products can be adapted very easily for pour-in-place countertop projects. These projects are challenging because concrete can set very quickly, making it difficult to pour a large area and trowel the entire surface before the concrete hardens. With our NeoMix Original System Products, you can increase your work time by reducing the amount of admixture that you mix in. Whereas our NeoMix Pro-Formula admixture has a work time of approximately 25 minutes, reducing the powdered portion of our NeoMix Original Admixture by half will gain you up to an additional 90 minutes of work time.

You cannot however eliminate the admixture completely as it contains key ingredients necessary to strengthen your concrete countertop mix (you want to keep and use all the micro-reinforcement fibers that come in the admixture). If you reduce the admixture, please remember to allow for a longer curing time (2-3 additional days) prior to de-molding and grinding/polishing.

Another important note is that most pour-in-place countertops will not have decorative aggregates as most people leave the troweled finish untouched. If you are planning on grinding, you can try to sprinkle decorative aggregates (see Decorative Inserts) on the surface of the countertop during troweling for a more unique finish.

The mix is more difficult to trowel than ordinary mixes — much "stickier." Try a small area first to see if you are comfortable with its workability before committing to a large countertop project.

For more information about the pour-in-place technique, refer to Appendix B, "Pouring a Countertop in Place", in Concrete Countertops.

Cheng Design does not specialize in pour-in-place countertops because we prefer the benefits of precast, or cast-in-mold, countertops. Nevertheless, we realize that in certain applications and situations the pour-in-place technique is a viable solution for some professionals or DIYs.

We prefer pouring our concrete countertops into a mold for better control of the surface, absolute flatness, and therefore less need for labor-intensive grinding. Hand-troweling the surface of a poured-in-place mold is an art unto itself. Troweling causes the concrete to settle differently than it would if left alone.

Specifically, troweling can bring the micro-reinforcement fibers (also known as "stealth" fibers because they are meant to lie beneath the surface) to the top of the countertop becoming visible, whereby requiring them to then be picked out or burned off. For more information on hand-troweling, refer to Appendix 3, "Pouring A Countertop In Place", in Concrete Countertops.

Screed the countertop piece with absolute precision, and have an expert trowel the surface. Timing and feel are critical in getting a flat, smooth finish. If you're planning on lightly grinding and polishing the concrete after it has cured sufficiently (4 days or more, depending on your mix design and cure time), you'll want the flattest surface possible to avoid extra grinding work.

Ultimately, however, a troweled finish will never be as even, smooth, and glossy as a precast countertop. For more information about pouring a countertop in place, refer to Appendix B, "Pouring a Countertop in Place", in Concrete Countertops.