Competing with Mass-Market Products

Question:
I’m worried about the solid-surface countertop people getting into the mass production of concrete countertops and ruining my market. How can I deal with this competition?

Answer:
It’s understandable to be wary of new competition, especially when that competition deals in mass-market products. And it’s easy to assume these new competitors will undercut prices and ultimately reduce the demand for concrete countertops. If you do nothing to change or adapt to the situation, then your worries will probably come true. But sometimes change is good, and you can use this to strengthen your market position by offering things the new competition can’t.

Concrete countertops are appealing to many people because they are custom, because of the artistry and creativity that goes into them, and because concrete itself has a different look and feel from other materials. You can better focus on these unique characteristics more than a mass-production shop can because you have the skills, time, creativity and business identity that caters to that level of customization. A mass-production shop will tend to be limited to a few standard colors, shapes and simple textures. Also, many solid-surface companies focus on commercial work. You could then focus on residential work, which often has more high-end clients wanting custom countertops.

If you’ve been in business for a while, you have built up a reputation with the builders and designers in your area. They trust you to continue to do good work, and this won’t change just because someone new comes along. Continue to strengthen these relationships and emphasize your experience and ability to meet the sophisticated tastes of their clients.

Having an experienced solid-surface company start making concrete countertops can actually be a good thing. In fact, it can help increase the demand for concrete countertops and allow you to keep your prices high. Most experienced solid-surface shops are profitable businesses that know what quality is and how to deliver on time. They understand the countertop process, the importance of scheduling and the need for production efficiencies. Their experience helps prevent trouble with their products and improves the quality of their installations. All of this increases the public’s confidence in concrete because they’ll be providing good examples of what concrete can be like, rather than delivering a poorly made sidewalk-grade countertop that degrades concrete’s image. This competition can also improve your business acumen because you must become more efficient and timely.

The more concrete is used in new applications, the greater the exposure and the more people’s comfort level will increase. And the more good examples of concrete countertops that are seen, the more people’s perception will improve. All this, in turn, will improve demand.

Proper Dosage of Pozzolans in Concrete

Question:
When I’m using pozzolans in concrete countertops, what’s the best dosage rate?

Answer:
Generally pozzolans replace some of the cement in concrete. Because they are treated like cement, the total cement content in the concrete mix does not change. This keeps color formulas and admixture dosages consistent. However, simply adding pozzolans to a mix without reducing the total cement content can alter your colors and admixture proportions.

The pozzolan replacement dosage depends on which pozzolan you use. Fly ash and slag, for instance, often replace 20% to 40% of the cement, while silica fume generally only replaces 5% to 10%. The differences often have to do with the reactivity of the pozzolan and how it affects workability. Both fly ash and slag are not as reactive as silica fume, and both enhance workability. Silica fume, on the other hand, inhibits workability, sometimes described as “increasing water demand.” This is a troublesome description because adding water to increase workability often has other negative effects, such as altered color, lower strengths and higher porosity. Superplasticizers are the better choice and can help create a very workable concrete with a low water-cement ratio.

Here are some typical dosages for common pozzolans:

• Fly ash, Class F: 15% to 25%
• Fly ash, Class C: 15% to 40%
• Slag: 20% to 50%
• Silica fume: 5% to 10%
• Metakaolin: 10% to 15%
• VCAS (vitreous calcium aluminosilicate): 5% to 25%

Replacing large portions of the cement with pozzolans (especially the ones that are waste products) is a good way to make your concrete “greener,” or more sustainable, because the production of portland cement releases large amounts of carbon dioxide, a greenhouse gas. However, doing this sacrifices the early strength of concrete (usually that attained at 7 days or earlier). In general, the greater the pozzolan replacement, the greater the reduction in early strength. Most pozzolans only improve the concrete’s strength after a few weeks of curing.

To confirm this, I cast some concrete test cylinders using two identical concrete mixes. One contained gravel, sand, gray portland cement, water and a plasticizer. The other was identical, but 10% of the cement was replaced by VCAS, a popular white pozzolan used by many concrete countertop makers. Compression tests performed by an independent test lab showed that the 3- day compressive strength of the VCAS cylinders was 9% lower than the straight portland cement cylinders, and the 7-day compressive strength was 7% lower. I chose these times because early strengths are important for crack-free handling and processing of countertops. The 28-day strength of the VCAS concrete was undoubtedly higher than the plain portland cement concrete, but with countertops, long-term strength is not as important as early strength.

It’s important to realize that pozzolans work with portland cement but won’t work with CSA cement (calcium sulfo-aluminate). CSA does not generate calcium hydroxide, so there’s nothing for pozzolans to react with. (For more information, read The Pros and Cons of Using CSA Cements.)

What Are Pozzolans?

Question:
What are pozzolans, and how do they work? What are the benefits of using them in concrete countertops?

Answer:
Pozzolans, also known as supplementary cementitious materials, are mineral admixtures added to concrete to improve its properties. Pozzolans react with the calcium hydroxide produced during cement hydration to form calcium silicate hydrate. In this way, the pozzolan is activated by the calcium hydroxide to behave like a cement.

When portland cement is added to water, a series of chemical reactions begin. One important reaction starts creating the “glue” that is responsible for the concrete’s early strength. Another starts later and is responsible for the concrete’s long-term strength. Other reactions happen too, and one of these is the generation of calcium hydroxide, or CH. CH provides no strength on its own. It simply takes up space in the concrete, and when dissolved with water can leach out and form efflorescence. Pozzolans react with the calcium hydroxide to form more of the beneficial glue that holds everything together. And because they consume the calcium hydroxide in the process, they fill the spaces the CH occupied, making the concrete less porous and less likely to effloresce.

The original pozzolan was pozzolana, a volcanic ash used by the Romans to make their concrete. Common pozzolans today are fly ash, silica fume, slag, metakaolin and VCAS (vitrified calcium aluminosilicate). Most pozzolans are waste products, and using them in concrete keeps them from ending up in a landfill. For example, fly ash comes from burning coal, silica fume from silicon production, and slag from steel refining. VCAS and metakaolin are manufactured pozzolans, but tend to be more consistent in performance because they are purposefully made. Note that the chemical makeup of the different pozzolans varies, and that can affect the color, reactivity and other characteristics of concrete, such as workability.

How Does Temperature Affect Concrete During Casting?

Question:
How does temperature affect my concrete countertops during casting, and what are some measures I can take to help control temperature?

Answer:
Temperature plays a significant role during concrete casting and curing. Like most chemical reactions, the hydration rate of cement is affected by how hot or how cold it is. Warmer temperatures speed up the reaction, and cooler temperatures slow it down.

Once mixed, cement and water start reacting immediately. Depending upon the temperature, the initial set can occur within 30 minutes to as long as several hours. Cooler temperatures permit longer work times, but early strength suffers. Hot temperatures shorten work time but yield higher early strengths.

After the concrete sets and begins to gain strength, the rate at which its strength increases depends upon the concrete’s temperature. For example, concrete placed outdoors in the winter at 50° F gains strength very slowly, while in the summer, concrete placed at 90° F gains strength much quicker.

Similarly, when you can safely strip your concrete countertops and start handling them largely depends on how strong they are at a particular time. If you normally let your concrete cure in the mold for three days, but colder temperatures have retarded the strength, the concrete won’t be as strong as you expect. As a result, the concrete could crack from being handled while it’s still weak, and honing or polishing might not produce the desired results. For example, if the cement paste is weak, polishing may cause tear-out as the diamond discs grab the sand grains and pull them out of the weak paste.

Typically there are two ways to deal with hot or cold temperature extremes. One way is thermally, the other is through chemical admixtures. If curing conditions are too cold and you want to accelerate set time and strength gain, using hot water instead of cold water will speed up the initial reaction. The hot water will warm the ingredients, temporarily making them warmer than the ambient surrounding temperatures. As the concrete cools down, the effects of the hot water are reduced. But strength gain will still be higher than if cold water was used. Another method is to use insulation or even heating blankets (or steam) to warm the concrete after it’s cast.

Acelerating admixtures like calcium chloride, calcium nitrate and calcium diformate all speed up the set time, and some influence the early strength gain. However, you should never use calcium chloride in concrete countertops (or other decorative concrete) because the admixture can alter the color.

If it’s too hot and you want to slow down the set time, using cold water or even ice as part of the mix water can cool the ingredients, slowing set time. You can use the ice pound for pound as mix water, but be sure it’s fully melted before discharging the concrete from the mixer. Ice is much more effective at cooling than cold water because the phase change from solid to liquid absorbs 80 times more heat than simply warming an equal amount of cold water.

Retarding admixtures can help delay the set time of concrete too. While table sugar can be used (with extreme care), commercial retarders are much more reliable, easy to use and have far fewer negative consequences if accidentally overdosed.

How to Expose Aggregate Inside an Integral Sink

Question:
I’ve had great success exposing aggregate on flat countertop surfaces, but how do I expose aggregate inside an integral sink? Are special tools or procedures required to work around curves and inside corners?

Answer:
Exposing aggregate in a concrete countertop, whether the aggregate is stone, glass or some other material, takes effort and time. Generally a very aggressive (low-grit) diamond pad or metal-bond turbo cup is needed to grind away the surface to expose the aggregate. Finer-grit pads are subsequently used to remove grinding marks and to smooth and refine the surface. As you’ve experienced, this process is fairly straightforward for flat countertop surfaces.

Working inside an integral sink is another story altogether. Often the sink’s shape is curved or complex, and access is tight. It may be physically impossible to get an electric polisher inside the sink. And using an aggressive turbo cup is often out of the question because of the sink’s curved surfaces.

A 3-inch-diameter backer pad with an extra-thick foam backer lets a 4- or 5-diamond polishing disc conform to the inside of a curved sink. While any thin, flexible diamond polishing disc will work, discs that have large diamonds, cut aggressively and have large spaces to flush the cuttings out from under the pad face work the fastest. I prefer DX Series Ultra Speed discs, sold by Granite City Tool. These pads last a long time and are particularly aggressive. While not extremely flexible, they will conform to the inside of a curved sink bowl.

An alternative to an electric polisher is to use a pneumatic polisher with a small flexible backer and large aggressive disc. I’ve already talked about the advantages of pneumatic polishers in a prior entry (see Pneumatic vs. Electric Polishers) so I won’t repeat that here. What matters in this case is that pneumatic polishers are much smaller and can often fit down inside a sink.
You can’t use rotary polishers inside all sinks, however. If your sink has corners, round discs won’t fit into them. So either you’re left sanding by hand, or you don’t expose the aggregate at all. Sometimes there are no easy answers for sinks like this.

It’s possible to expose aggregate inside a curved sink basin, but you’ll need some special tools.

A 3-inch-diameter backer pad with an extra-thick foam backer.

DX Series Ultra Speed discs.

A pneumatic polisher.

Combining the pneumatic polisher with the small flexible backer and 4- to 5-inch diamond disc will allow you to maneuver inside a sink basin.

If your sink has corners, round discs won’t work. To expose the aggregate, you’ll have to sand by hand.

UV-Activated Sealer Cures in Seconds

Question:
I’ve heard about a new countertop sealer on the market that reacts with ultraviolet light. How does the sealer work and is it any good?

Answer:
The new sealer, called Counter-UV, manufactured by Kinloch and distributed by Surface 519, uses high-intensity ultraviolet (UV) light to cure the finish. It is formulated specifically for concrete countertops. While UV-curable finishes are common in the cabinet and flooring industries, a UV- curable sealer for concrete is a rarity. Historically, bonding issues have been the problem, but the manufacturer seems to have solved that with this product.

The finish itself is a specialized single-component, urethane-acrylic blend. It has no VOCs and offers excellent color enhancement, excellent stain resistance, and almost total acid resistance. Concrete Countertop Institute stain tests showed that only mustard left temporary discolorations in the sealer, and those could be easily and completely removed with household bleach. Very few sealers are completely resistant to mustard.

What makes this product so different from other high-performance sealers is how it cures. Most finishes, especially multicomponent products, can take hours to become tack-free and several days after that to reach full cure. Single-part finishes often merely need to dry out, so they become handleable faster. With the UV sealer, high-intensity, short-wavelength UV light initiates the cure. After exposure to the light for only a few seconds, the finish is ready for use. Thus you get the speed, convenience and ease of a single-part finish with the top-of-the-class performance offered by the best multipart finishes.

The UV sealer can be rolled on, sprayed on or wiped on. Rolling with a low nap (3/16- to 1/4-inch) lint-free roller is preferred, since the finish will flow out over time into a smooth film. Once applied, the finish does not cure and will not get hard, sticky or gummy until exposed to UV light. This is a great advantage because you can let the wet finish flow out or squeegee and back roll it repeatedly before curing.

You also have ability to adjust the sheen from high gloss to dead flat. If a glossy finish is not desired, you can sand the cured sealer to achieve whatever sheen level you’re after. But it’s best to use specialty sandpaper made for the solid-surface industry rather than ordinary woodworking sandpaper, which is not graded finely enough and can leave scratches in the finish. While these sanding discs are more expensive, they have very tightly controlled abrasive particle sizes that leave a uniform, scratch-free surface.

As with any finish, this one has its cons to go with the aforementioned pros. The finish will only cure with a specialized, high-intensity UV light. Sunlight, tanning lamps or fluorescent UV bulbs will not do the job. This UV light is expensive—about the same price as a large, high-quality concrete mixer. Because of this, it is cost prohibitive to try a sample of the finish, because without the UV light, the finish will not cure.

A white GFRC desk sealed with Counter-UV.

Unless you want a high-gloss finish, the only way to get a lower sheen is to sand it. And because it’s a tough, scratch-resistant finish, sanding takes time. Curved surfaces and intricate molded edging can be a challenge, too, and will require effort and skill to achieve high-quality results.
While some of these disadvantages seem significant, the system as a whole saves you the time of waiting for a finish to cure. It also is one of the easiest finishes on the market to repair, since repairs blend in well.

How Do I Design My Own Concrete Mix?

Question:
Currently I use a prepackaged concrete countertop mix, but I’m thinking about coming up with my own mix design. Is it worth the effort, and what’s involved?

Answer:
Designing your own concrete mix for concrete countertops is a rewarding endeavor. It gives you a mix that you understand and have significant control over. And because it’s made from ingredients you’ve chosen, are probably local to you and that you buy in bulk, it’s much less expensive than bagged mixes.

However, making a custom concrete countertop mix that performs well in the long run is not easy. It requires an understanding about the fundamentals of how concrete works, how all the ingredients interact and affect each other, and just as important, what kind of performance characteristics are essential for concrete countertops. There is not a universal, one-size-fits-all concrete mix.

Different mixes provide different looks and may require different casting methods. A mix tailored for a stiff, hand-packed casting method is not likely to be good for wet casting, which requires a highly fluid mix optimized for speed and use with complex forms. While the workability characteristics are the most obvious differences between mixes, their strength and shrinkage characteristics play a major role in how the concrete performs, both in the short and long term.

Concrete mixes are often described in a form of shorthand. The classic “3:2:1” mix (three parts aggregate, two parts sand and one part cement) is a good example. This shorthand is extensively used in the industry, but it fails to describe the subtle but important characteristics that make one mix great for concrete countertops and another mix a poor one. This shorthand is akin to describing a car by simply stating it has four doors, a 2-liter engine and is red. Not terribly descriptive, nor does it tell you anything about how the car will perform. It really tells you more about what it’s not than what it is.

Without getting into the details of the mix design procedure, it’s important for you to understand that there’s a lot more to creating a mix than simply collecting a bunch of ingredients and the most popular or readily available admixtures and combining them according to someone’s recommendations. What works for one person may not work for another because variations in local aggregates (size, shape, roughness, gradation, mineralogy, etc.) all play a significant role in how the concrete performs. You need to look at the background, experience and qualifications of the person giving the advice. If they don’t understand what’s necessary, how can they help you with what you need?

I’ve written a series of articles on mix design that can give you guidance and insight into what’s important and what’s not. These two articles, in particular, are a good place to start:

• Bagged versus DIY Mixes


• The Role of Aggregate in Concrete Countertop Mixes

Another great resource, although very technical and rather advanced, is “Design and Control of Concrete Mixtures,” a publication by the Portland Cement Association (http://www.cement.org/).