Mixing + Pouring a Concrete Countertop

Q1: Why use Sakrete 5000-Plus or Quikrete 5000 for my concrete countertop?

Sakrete 5000-Plus and Quikrete 5000 are sacked concrete mixes or "concrete composite products" that are pre-packaged mixes of the individual ingredients that make up concrete (including graded sands, aggregates, and cementitious material). Both of these mixes are rated to withstand pressures of up to 5000 pounds per square inch (PSI) when fully cured, resulting in a denser, harder, and more durable surface. Any sacked concrete product rated at 5000 PSI is appropriate for use with both CHENG Pro-Formula Concrete Countertop Mix and the NeoMix Original Products.

Q2: Can I use ordinary pre-mixed, bagged concrete?

We don't recommend using ordinary sacked (bagged) concrete which has not been rated as a 5000 PSI mix, or higher.  In order to make a quality concrete countertop, you need to use a concrete mix that achieves a hardness of 5000 PSI or greater in order to polish the surface to a desirable shine. Softer concrete, those under 5000 PSI, makes it difficult to polish very well as the cementitious bond is too weak, leaving you with a dull, irregular surface regardless of how much you polish. When using either CHENG Pro-Formula Concrete Countertop Mix or the NeoMix Original System, we strongly recommend the higher quality sacked concrete such as Sakrete 5000-Plus or equivalent.

Q3: My local home improvement centers and builders' supply yards only offer ordinary bagged concrete mixes. What should I do?

Make your own by adding additional Portland cement to the ordinary bagged concrete. You can convert ordinary bagged concrete into 5000 PSI concrete by adding 6 lbs. of Portland cement to every 120 lbs. of ordinary bagged concrete mix.

Q4: I've been told I can make my concrete countertop "greener" by replacing up to 30% of the Portland Cement in my mix with fly ash. Is this correct and do you recommend it?

Yes...and No. Fly ash is post-industrial waste from coal-burning electrical power generation plants. When we add fly ash to concrete, we divert it from going to landfills, thereby making our concrete "greener."  However, we do NOT recommend using fly ash in concrete countertop mixes due to it's wildly unpredictable impact on the ultimate color and appearance of the countertops. For a fly ash alternative to create "green" concrete projects, where the color and ultimate appearance are important, we use a predictably stable post-industrial waste cement replacement called VCAS-160.

Q5: I see that CHENG Concrete endorses Sakrete 5000-Plus Premium Sacked Concrete for making concrete countertops—why?

Sakrete 5000-Plus has been specially developed for the decorative concrete industry. It's free of admixtures and additives (such as flyash) known to adversely impact color results and workability. Some admixtures us ed by other brands also make the concrete "sticky" and more difficult to finish.

Q6: Can I use white Portland cement?

If you use white Portland cement, the color of your countertop will be much lighter when fully cured than CHENG Pro-Formula and NeoMix color samples. If you want to use white Portland cement, we recommend you read Chapter 3, "Mix Design," in Concrete Countertops for a more detailed discussion.

Q7: Will micro-reinforcement fibers show in my finished countertop?

The micro-reinforcement fibers in the NeoMix Original System are designed to seamlessly disappear into, and bond with, your concrete mixture. If they do accidentally appear, they can be easily burned off using a light torch or flame.

Q8: How do I know when I've achieved the right concrete mix consistency?

Like bread-making, you'll know you've achieved the right mix when it looks and feels right. Pick up a handful of the mix and pour it back and forth from hand to hand to see how it behaves—a proper mix consistency looks and feels like soft or runny oatmeal. For more information, refer to Chapter 3, "Mix Design," in Concrete Countertops.

Q9: How do I get a streaked or swirled countertop finish? Can you add pigment to the mix and stir it in, like making a marbled cake?

To create a streaked or swirled finish, place concentrated patches of colored concrete onto the mold and let them stiffen a bit before adding the bulk of the mix. Carefully vibrate to keep the batches separate from one another.

Q10: When pouring, how much work time do I have with the concrete mix?

Plan and prepare! At 70º-80ºF, you'll have approximately 40 minutes of work time. Therefore, plan ahead and have your project mold, mixer, water and tools all in place prior to mixing the concrete. You should have plenty of time to complete your concrete countertop project, but be prepared with your materials and tools and work briskly. If your concrete is warmer, you'll have less work time and, if it's cooler, you'll have more work time. If your concrete materials have been stored outside in a freezing environment, bring them inside and allow them to warm to room temperature before mixing.

Q11: I just poured my countertop and it doesn't look like the exact color I ordered—why?

A freshly poured concrete countertop does not necessarily indicate the final, well-cured countertop color. Remember that:

1. final actual color will not be known until the countertop is fully cured, approximately 28 days later;
2. you are looking at the underside of a countertop which has not yet been, or will not be surface finished so is generally lighter in color;
3. the countertop will continue to evolve and generally darken as you seal and wax it;
4. due to the natural color variation of the cement used in the bagged concrete mix, coloring concrete is an imperfect science where there are never any guarantees in terms of matching an exact color. To help ensure consistent color on a project with multiple pours: a) buy all the same sacked concrete at the same time, and b) pour on the same day.

When working with concrete, be open to and prepared for a final product in the color range that you intended, but not necessarily exactly like the one that you used as a guide when you ordered. The uncertainty of each countertop pour (factors include climate and weather conditions) and the unique characteristics of each product are some of the dynamic and exciting aspects of working with concrete.

Finally, if you are thinking about exposing the aggregate (while polishing), keep in mind that sacked concrete is regionally produced so the type and color of aggregates will vary from region to region as well. So, if you fell in love with your brother's concrete countertop that was made in California, expect some variation in your countertop if you've selected the same countertop but you've made yours in Florida; these countertops will be close to one another in color but not exact. Final color is also affected by curing conditions and temperature. To ensure there are no surprises, we suggest making a 1 cubic foot sample pour, in the color of your choice, before pouring the actual project.

Q12: How long do I wait before I can de-mold my countertop?

After pouring a countertop, you can de-mold it after four days, at which point the countertop is at 85% of full strength (approximately 4250 PSI). For more information, refer to Step 4, "Out of the Mold", in Concrete Countertops Made Simple or Chapter 5, "Curing, Finishing, and Troubleshooting", in Concrete Countertops.

Q13: How long does it take for my countertop to fully cure?

Technically speaking, a concrete countertop continues to cure for years after it is poured. However, a countertop will achieve its full strength of 5000 PSI after just 28 days, which is when we considered it "fully cured" for all intents and purposes. For more information, refer to Step 4, "Out of the Mold", in Concrete Countertops Made Simple or Chapter 5, "Curing, Finishing, and Troubleshooting", in Concrete Countertops.

Q14: I've heard about countertops "curling" during the drying process. What can I do to prevent this?

There are many possible causes for "curling" but the common culprits are too much water in the mix and improper curing conditions.  Pro-Formula Concrete Countertop Mix has been engineered to minimize the risk of curling by requiring less water than conventional concrete mixes. You can also prevent curling by tenting the freshly poured concrete with painter's plastic to ensure that the concrete cures in a 100% humidity environment.