Even in the Cayman Islands, concrete countertops can be challenging

I love my job. I get to meet interesting people. I get to travel the world and help people be more successful with their concrete countertop businesses. And I make cool concrete.

I’m currently spending the summer down in the Cayman Islands helping out my student Terry with several large projects. (I’ve been there before – here’s a photo of the project I helped him with in December.)

Terry Grand Cayman

The first project I’m working on this summer is a 100 sq ft outdoor bar/gazebo. It’s a pretty simple job – just a hexagonal bartop.


But this experience is showing me that even when things seem simple on the surface, the little details which appeared insignificant at first suddenly become the critical factor that brings everything to a screeching halt.

This outdoor bar is a pet project of a local developer. They and their architect drew up plans in January for a hexagonal-shaped bartop in an outdoor gazebo. The design was unchanged up until a week ago, and we were given the go-ahead to start forming for pouring right away.

 forming gazebo

On the morning we started forming the architect halted everything and said the client changed the bar profile, reducing the overhang distance on the patron side and increasing the overhang on the bartender side. This was to allow for the beer taps to be installed in the bartop instead of on kegerators.

So new forms were cut and assembled. When asked about the details on the taps, the response was that they were pretty sure which ones were going to be used, but the details were not finalized. A few days later the tap details emerged, but it turns out the tap, its drip tray and the bartop don’t actually work together. Oops!

And guess what: The architect didn’t discover this. The owner didn’t. Terry and I did – the concrete countertop guys.

The morals of this long story are:

1. What seemed like a simple project that really was a lot more complex than it appeared.

2. You, the concrete guy/gal, need to understand a lot more than just concrete.

The fact that the plans were drawn (and re-drawn) before the taps were selected highlights the need for someone with experience, skill and an awareness of how everything will come together. The architect isn’t that person. The owner isn’t that person. It’s you. You must deal with the details that matter.

Sure, you have to know the basics of forming and casting and making concrete. That’s the easy part that everyone who offers training covers. But it’s the little details that have nothing to do with making concrete that are what separates those who are successful and make things work the first time from those who learn the hard way, through mistakes, expensive re-do’s and frustrated clients.

This is why I spend so much time on sinks, faucets and installation in my intensive class. The devil is in the details. Even in the paradise of Grand Cayman.

PS – Keep track of my Cayman adventures on Facebook. I’ll be posting lots of photos and updates.

PPS – Actually, “Hell” is in Grand Cayman. Here’s a photo.

Hell Grand Cayman

Coloring Techniques for Concrete Countertops: Part 3 of 3 – Dyes


The third method for coloring concrete countertops is by using dyes. Dyes, like acid stains, are applied to cured concrete, and they can be applied over integrally pigmented and acid stained concrete. Unlike acid stains, dyes are not reactive. Dyes are ultra fine particles of color in some kind of liquid carrier, most often water or solvent, such as acetone.

The ultra fine particles “stain” the surface while the liquid carrier quickly evaporates, leaving very little or no residue. This quick evaporation (especially with the solvent based dyes) can be both a benefit and a drawback. Most often they are sprayed on, but they can be brushed, rolled or wiped on. Brushing, rolling or wiping a quickly evaporating dye will almost always lead to streaks or blotching, so spraying is generally used to ensure an even coloration.

Dyes can provide a wide range of colors, from duplicating the colors of acid stains to rivaling the colors of integral pigments. Rich, vibrant colors are possible with dyes, and because they can be diluted, mixed and layered, the color possibilities are nearly endless. Like acid stains, dyes are slightly translucent. The finished color is dependent on both the color of the acid stain and the color of the underlying concrete.

While dyes provide great versatility, especially when used as an accent or an easy means of coloring specific areas or designs in the concrete, dyes can be limited to where they can be used. Not all dyes are UV stable, and some must be used under sealers that block UV light. Water based dyes tend to be less UV stable and can bleed or smear if a water based sealer is applied over them. Solvent based dyes tend to be more UV stable (but always check with the manufacturer to find where and when to use them), and these too can bleed or smear if a solvent based sealer is applied to them. And like acid stains, dyes only color the surface of the concrete. Their beauty is only skin deep.

A significant advantage that dyes have over acid stains is that because dyes are not reactive, there is no residue to clean up after the dye is applied. This means that they can be sealed almost immediately after application (once the liquid carrier evaporates), making the project faster.

And finally, like acid stains, dyes can be very cost effective because a little goes a long way, but again the skill does not come cheap. Dyes are often used by highly skilled artists to create stunning works of art on concrete.

Several photos and more information about dyes are available at http://www.concretenetwork.com/concrete/concrete_dyes.


If you are a homeowner who wants a unique countertop, talk to your local craftsman about the types of coloring options he or she provides.

Whatever look you want to achieve, it is possible with the myriad coloring options for concrete countertops.

Coloring Techniques for Concrete Countertops: Part 2 of 3 – Acid Stains

Acid Stains

Acid stains are another very common and effective way to color concrete. Like integral pigments, acid stains are permanent and most can be used inside and outside. Unlike integral pigments, acid stains are applied to the concrete only after it has cured. Integral pigments are used primarily because they are uniform and predictable. Acid stains are mostly used for exactly the opposite reasons.

Acid stains are chemical solutions that react with the concrete to form color. Each different acid stain contains a particular metallic salt that reacts with the calcium hydroxide in concrete; the acid makes the reaction possible.

Acid stains are reactive; for this reason, they are somewhat unpredictable, or as some people prefer to say, more spontaneous. While the color of the acid stain won’t vary much from what’s expected, the shade and intensity will. The intensity of the color is dependent on both the concrete and the acid stain. Since the acid stain reacts with the concrete, the age, ingredients, texture, curing method and finishing method (honed versus trowelled) all have a strong influence on the final result. And the stronger the acid stain solution (the less dilute it is) and the longer it is allowed to react with the concrete, the more intense the color will be. So the end result is a beautiful mottling of shades and intensities, where the exact end result cannot be predicted.

Acid stains come in a limited (but popular) range of colors. Browns, rusty reds, orangey-browns, bluish-greens and yellow-greens typify the colors commonly available. While the colors are generally the same or similar from manufacture to manufacturer, the strength of the acid may vary, and this influences the color. Acid stains are slightly translucent. The finished color is dependent on both the color of the acid stain and the color of the underlying concrete.

Acid stains form the color on the surface of the concrete. Smooth, dense, high quality concrete, which is very typical in concrete countertops, is not very porous. Acid stain color does not penetrate very far into the concrete. Typically it is only a few thousandths of an inch deep. Because of this the color can be worn off from prolonged abrasion, so some sort of sealer generally applied over the stain to protect it. This is more often a concern with floors than with countertops.

It is possible to mix some acid stains together, and it is possible to apply one color over the top of another acid stain. And acid stains can be applied over integrally pigmented concrete. This is a good method for getting the best of both worlds: achieving a particular color and overall evenness of tone but capturing some of the unpredictable mottling too.

Since acid stains are applied to cured concrete before it is sealed, only a small amount is needed to color a large amount of concrete. Typically a gallon of acid stain costs about $50 to $70, but will color several hundred square feet of concrete. This makes them very economical.

However, the skill involved in applying acid stains and knowing what effects will be achieved does not come cheap. It requires a great deal of experience and attention to detail. A craftsman who has experience in acid stained concrete floors is often a good candidate to apply his or her skill to acid staining concrete countertops.

Acid staining is also a popular technique in conjunction with stencils. Stains can be applied before and/or after stenciling to achieve a variety of effects.

 acid stained concrete - brown over copper with Modello stencil

Brown over copper with Modello stencil


Floral edge with amber acid stain

Traditional look achieved with amber acid stain and floral edge

Coloring Techniques for Concrete Countertops: Part 1 of 3 – Integral Pigments

There are three common methods for coloring concrete countertops. One way is by using integral pigments. Another way is to acid stain the concrete, and the third way is to use a dye. This article explains integral pigments.

Integral Pigments

Integral pigments are a very common method for coloring concrete. Pigments are very finely ground particles of inert colored material that are mixed into the concrete (usually during mixing, or sometimes during trowelling).

Integral pigments can be powders or liquids. They can be natural minerals, manufactured metal oxides or synthetic materials. Integral pigments offer the widest range of color options that span the entire spectrum. Pigments can be pure white, deep black, red, bright yellow, blue, purple, green, brown, orange, etc. Pigments can be blended into a nearly infinite range of shades and colors, offering virtually the same color range as the paint industry.

integral pigments

Integral pigments provide versatility and dependability. The strength of integral pigments is their huge color range and their consistency. Pigments are the most consistent and highly controlled ingredient in concrete. As long as careful batching, mixing and curing procedures are followed (paying special attention to controlling the mix water), the resulting color consistency can be very high. With integral pigments, it’s easy to achieve the same color and the same look over and over again, as long as the your concrete countertop craftsman is meticulous.

Integral pigments get mixed into the concrete, so the entire body of the concrete is colored (although there are methods that don’t require coloring all of the concrete in a slab). This means that significant quantities of pigment are required, and this leads to perhaps integral pigments’ downside. Some pigments are more expensive and harder to find. Pigment prices can range from $2/lb to over $60/lb, and while many of the standard iron oxide colors are widely available from a number of manufacturers, some of the more exotic colors are available from only a few small distributors. A concrete countertop craftman may charge more for concrete colored with some of the more exotic colors.

Here are a few pictures of concrete colors achieved with integral pigments.

Integral colors can be subtle:

sage green countertop

Soft sage green countertop


penny color with rustic edge

Penny colored countertop with rustic edge.


 Or bright:
turquoise embedded in bright red concrete

Piece of turquiose embedded in edge of bright red countertop


Aqua blue oyster bar with blue glass

Aqua blue oyster bar with blue glass


Or combined with other effects to create different looks. The following two countertops use a bit of black pigment to create a dark gray concrete, but then use stone and glass in different ways to create very different looks.

gracy concrete with stones

Traditional look achieved with gray concrete and cream/tan stones and traditional edge.


gray concrete with black grout and clear glass

Contemporary look achieved with gray concrete and black grout and clear glass.

The importance of water/cement ratio in concrete countertop mix design

Three simple ingredients can be blended and proportioned numerous ways to make concrete:

  • aggregate
  • cement
  • water

In concrete, the single most significant influence on most or all of the properties is the amount of water used in the mix.

In concrete mix design, the ratio of the amount of water to the amount of cement used (both by weight) is called the water to cement ratio (w/c). These two ingredients are responsible for binding everything together.

The water to cement ratio largely determines the strength and durability of the concrete when it is cured properly. The w/c ratio refers to the ratio of the weights of water and cement used in the concrete mix. A w/c ratio of 0.4 means that for every 100 lbs of cement used in the concrete, 40 lbs of water is added.

Typical w/c ratios are as follows:

  • Normal for ordinary concrete (sidewalks and driveways): 0.6 to 0.7 
  • Specified if a higher quality concrete is desired: 0.4

The practical range of the w/c ratio is from about 0.3 to over 0.8.

  • A ratio of 0.3 is very stiff (unless superplasticizers are used).
  • A ratio of 0.8 makes a wet and fairly weak concrete.

Typical compressive strengths when concrete is properly cured are:

  • 0.4 w/c ratio –> 5600 psi
  • 0.8 w/c ratio –> 2000 psi.

The simplest way to think about the w/c ratio is to think that the greater the amount of water in a concrete mix, the more dilute the cement paste will be. This not only affects the compressive strength, it also affects the tensile and flexural strengths, the porosity, the shrinkage and the color.

The strength is reduced mostly because adding more water creates a diluted paste that is weaker. Think of it like over-diluting grape Kool-Aid. The more water you add, the weaker the Kool-Aid is.

grape koolaid

Explained more technically, more water results in larger spacing of the cement particles. As the crystals grow, they are too far apart to knit together and form strong bonds.

cement particles

Concrete with a higher w/c ratio is also more susceptible to cracking and shrinkage. Shrinkage leads to micro-cracks, which are zones of weakness. Once the fresh concrete is placed, excess water is squeezed out of the paste by the weight of the aggregate and the cement paste itself. When there is a large excess of water, that water bleeds out onto the surface. The micro channels and passages that were created inside the concrete to allow that water to flow become weak zones and micro-cracks.

Using a low w/c ratio is the usual way to achieve a high strength and high quality concrete, but it does not guarantee that the resulting concrete is always appropriate for concrete countertops. Unless the aggregate gradation and proportion are balanced with the correct amount of cement paste, excessive shrinkage, cracking and curling can result. Good concrete results from good mix design, and a low w/c ratio is just one part of a good mix design.

Curing: An essential step to create high quality concrete countertops

Curing. We all know it’s important, but what exactly is it, why is it important and what factors affect curing?

Adding water to portland cement starts a chemical reaction called hydration. As hydration proceeds over time, the portland cement and water are transformed into beneficial calcium silicate hydrate (CSH) compounds. These compounds are the glue that hold the aggregates together, creating the hard, solid material we know as concrete. There are other compounds that form during the hydration process, but they are not responsible for strength.

Portland Cement + Water = CSH (provides strength)

Curing is the process of maintaining moisture levels inside cast concrete so that hydration can continue. As long as free moisture and unhydrated cement exist inside the concrete, the strength, hardness and density will gradually increase. Practically speaking, curing is simply the process of keeping the hardened concrete moist so that it can continue to gain strength.

As the concrete gets stronger and denser, its porosity decreases. This is important, because early on the concrete is much more porous than when it’s older and has hydrated longer. Porous concrete loses moisture to evaporation quickly, and this can lower internal moisture levels and stop hydration. If the concrete dries out, it stops gaining strength. This is why it is so important to cover your concrete right after casting and keep it moist. When concrete dries out, it dies, just as a tomato seedling would die if it weren’t watered.

tomato seedlings watering can

When concrete is mixed, all the water needed for full hydration is present in the mix design. Often contractors add more to the concrete than needed for hydration, to make the concrete more workable. This extra water is called water of convenience. This extra water causes the cement particles to be too far apart to knit together into a strong matrix. It results in a longer set time and lower strength.


Cement particles that are too far apart can’t knit together.

Very powerful superplasticizers make it possible to remove almost all of the water of convenience, leaving a little bit more than just the water needed for hydration. This is the ideal blend of just enough water for hydration, but not so much water that the cement particles are spaced too far apart.

It’s actually rare that concrete is cured until most of the cement is hydrated. This generally takes months or years to occur. Rather, the concrete is cured for as long as you need it to be to reach the desired strength. The length of curing time can vary widely depending upon the structure or item made out of the concrete, the mix design, the concrete’s temperature and the desired strength at a certain time, to name just a few factors.

For concrete countertops, clients are not willing to wait 28 days for their concrete to be delivered. Because of this, mix designs tailored for concrete countertops have high early strengths so that the concrete can be cast, cured, processed and delivered in a couple of weeks (or less). For example, ordinary construction grade concrete often achieves a compressive strength of 4000 psi in 28 days. It’s not unusual for a mix design for concrete countertops to reach that strength in only 2 days. With some advanced mixes, this can be achieved in a matter of hours. So for a particular design strength, different mixes require different curing times.

Another factor that will influence the curing time is temperature. Colder concrete gains strength much slower than warmer concrete. At 3 days after casting, concrete cured at 45 degrees F only has about 70% the strength of the same concrete cast at room temperature (73 degrees F). In contrast, concrete cast and cured at 90 degrees F has about 10% more strength than concrete cured at 73 degrees F. Over time these differences gradually become smaller, but often it’s the early (2 to 3 day) strength that is more important than the 28 day strength.

So remember, don’t use more mix water than you have to, keep your concrete evenly moist for at least the first couple of days, heat it if necessary. All this will allow your concrete to cure and strengthen. You will end up with higher quality concrete countertops and happier clients.

An easy way to create eased edges on a concrete countertop

Easing the edges around sink openings in concrete countertops is important to prevent chipping and to provide clients with a smooth, comfortably rounded edge. There are a couple of ways to do this: shape the edge by hand after casting, or form the roundover before casting.

While shaping the cast concrete is practical for straight edges or outside curves, it’s often difficult to do on tight, inside curves like those found in an undermount sink opening. And getting a smooth, even curve does take some practice, even with a special grinder and roundover bit.

One way to form a roundover before casting is to run a bead of caulk and carefully smooth it to the right radius, and then let the caulk cure, usually overnight. While this works, it’s time consuming, messy, and getting it right takes practice.

Try this instead: Get some non-hardening plastic modeling clay from the craft store. Any color will do! Roll out a rope of clay about 1/4″ diameter (or more for bigger roundovers) and pack it into the corner or edge to be rounded over.

Next, make a shaped scraper. A piece of thin wood template stock works, but an even better (and free) scraper is made from a laminate sample chip. Sand or file a different radius onto each of the 4 corners: 1/8″, 3/16″, 1/4″, 3/8″, or whatever you want. You can even do bevels or other shapes too.

Once the clay is packed in the corner between the form side and the casting table, scrape the excess clay away using the scraper. The radiussed corner will cut and scrape a smooth, even shape into the clay. The form is then immediately ready for oiling and casting.

Once stripped, the clay can be pulled from the concrete and reused. A degreaser like Greased Lightning makes short work of any clay residue, and a power washer gets out any clay that becomes smeared into the voids.

Modeling clay for edging

Making a tie-dyed concrete countertop

As a fun follow-up to my Achieving Color Consistency series, I thought I’d post some photos of a crazy “tie-dyed” concrete table I made. You could use this technique with a concrete countertop and with any combination of colors.

The process was actually quite simple. I just used extra-bright synthetic pigments, some liquid and some powder, and mixed very small batches.

mixing tiny batch


Once I had the colors ready, I applied them in a pattern to match a photograph.

starting swirls

adding colors

Then I poured bright white concrete over the whole thing.

adding white

The colors got a little smeared in the finished table, but I think it looks far-out and groovy, man!

finished table

Achieving color consistency in concrete countertops: Part 3 of 3

You have learned that water strongly affects the color of a concrete countertop mix, as does precision of measuring and measuring by weight, not volume. This final article in the color consistency series lists several other reasons you might encounter inconsistency in your concrete countertop mixes.

  • Variability in the ingredients themselves

From year to year, the ingredients you use can vary, even if you buy the same ingredient from the same manufacturer. Pigments tend to be very consistent, but cements, especially gray cements, are not. Your colors that have less pigment, and therefore obtain most of their color from the cement, will exhibit more variability thann heavily pigmented colors.

  • Use of pozzolans

You may use pozzolans such as metakaolin, VCAS, fly ash, slag or silica fume in your mixes. Some of these pozzolans, especially waste products such as slag, can be highly variable in color. And, pozzolans such as silica fume can impart a very distinct color to the concrete. Besides the fact that different pozzolans have different actions and properties, you should not vary which pozzolans you use in your mix designs if you want to achieve color consistency.


Various pozzolans. Photo courtesy www.cement.org

  • Use of admixtures such as superplasticizer

Admixtures like superplasticizers can influence color, not because they add color, but because they can act like dispersants, aiding in cement and pigment dispersion and the resulting color strength. Other admixtures usually have little effect on the color, like fibers, accelerators or retarders, however calcium chloride accelerators are an exception and should be avoided for this and other reasons.

  • Not blending ingredients thoroughly

Thorough and complete blending of all of the concrete ingredients is very important to achieving a uniform and consistent color. All of the pigment added to the mixer should be uniformly blended. If pigment is stuck to the sides of the mixer or in lumps or streaks then the resulting concrete will not be consistent with other batches nor will the color of that batch be uniform.

  • Adding liquid pigment to the mix water

Adding liquid pigment to the mix water before adding the now pigmented mix water to the concrete can cause color inconsistency because a significant amount of the pigment usually remains in the bucket.

Liquid pigments are really ultra fine pigment particles suspended in a liquid. If the liquid pigment is added to mix water, the pigment particles will quickly settle out because the suspension fluid is now greatly diluted by the mix water. No amount of stirring will suspend all of the pigment particles, so much of the color remains in the bucket rather than going into the mixer.

When done carefully, it is possible to add the liquid pigment to a portion of the mix water and then use the remaining mix water to rinse out any pigment residue.  But this involves extra work and requires extra attention. A simpler process would be to add the liquid pigment directly to the mixer and then to rinse out the pigment container with the mix water as it is added.

  • Inconsistent curing practices

Curing the concrete has an effect on concrete color. Curing the concrete after casting helps “lock in” the color. If some slabs are allowed to wet cure for longer than others, the slabs that dry out sooner will appear lighter.

  • Forms

Forms for fluid concrete mixes must be watertight in order to achieve consistent colors. Otherwise, color variations will show where some of the concrete leaked out of the forms. Form materials themselves (the texture and porosity) can affect the color of the concrete too.


Everything that goes into making concrete has some effect on its appearance. Discipline, attention to detail and knowledge of good concrete practices will make your concrete countertops as consistent as possible.

Achieving color consistency in concrete countertops: Part 2 of 3

The last article talked about the importance of measuring ingredient precisely, especially water. It is also very important to understand that you must measure by weight, not by volume.

Suppose a mythical concrete countertop mix included cotton balls as one ingredient and golf balls as another. Clearly a much larger volume of cotton balls would be needed to make one pound, versus one pound of golf balls.

There are some ingredients which seem to have consistent weight-volume conversions, such as water. You know that one quart of water is 32 (fluid) ounces. So you could just measure your water using a container with ounce or quart markings on it, right?

Not so. Measuring containers are typically not designed to a high degree of precision. Watch this video to see why using measuring containers can lead to errors and inconsistency.

Achieving color consistency in concrete countertops: Part 1 of 3

Integrally colored concrete countertops can show color inconsistency for a variety of reasons, but the primary cause is lack of ingredient control: One or more of the ingredients in each batch of concrete were not carefully proportioned.

Most often the culprit is water. Adding too much water – often to increase the workability – will alter the color of the concrete, making it lighter than a similar batch that has less water in it.

Think of grape Kool-Aid. The more water you add, the lighter the color will be. The same applies to concrete. (The concrete will also be weaker, just like the Kool-Aid will taste weaker.)


Remember, water is the most critical ingredient in concrete, and casually adding water without keeping track of the exact amount will almost guarantee an inconsistent appearance. To ensure color consistency, ALL of the ingredients, including water, must be accounted for.

The simplest way of doing this is to generate a batch report, where each ingredient amount is listed next to a check box. The batch report ensures consistency in ingredient amounts, and the check boxes ensure that none of the ingredients gets left out.

The CCI mix calculators, both the Precast Concrete Countertop Mix Calculator and the GFRC Concrete Countertop Mix Calculator, print out batch reports. Whatever method you use to calculate your mix, make sure that you are diligent about using batch reports.

Last updated by at .