Tag Archives: pigments

Using different mixes in a single concrete countertop slab

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I recently got the following question regarding my blog post “Mix design for cast in place concrete countertop in Cayman“:

Q: Is it possible to use gray cement for the core and white cement as an outer layer?

White and gray portland cement are very similar to each other, and can be safely blended together. You can use one color cement for a core mix and a different color cement for a shell mix, provided the mix designs and the water/cement ratios are identical.

However, I would hesitate to use a gray cement core with a white cement “shell” for aesthetic reasons, especially for projects like the cast-in-place gazebo I did in Grand Cayman, and for regular precast “wet cast” projects. The simple reason is that it’s very impractical to pour a core mix without contaminating the form surfaces, contain the core mix so that it stays where you want it, and to pour the visible shell mix and still end up making good concrete without voids or weak zones. The minor cost savings in cement (white cement in Cayman is about US$20 per bag, vs gray cement at US$10 per bag).

The exception is when an ultra-expensive pigment is involved. In that case it is sometimes worthwhile in cost savings to take the extra trouble to use the pigment only in the outer layer.  I call this “buttering”. It is easier to do with a hand packed precast method, somewhat easy with GFRC, and hardest with wet cast precast or cast in place. Be aware, however, that some exotic pigments could affect the properties of the mix to the extent that you have issues with the 2 layers bonding.

Tips for “buttering”:

  • The first layer should be well compacted, of even thickness and fairly smooth. Loose, clumpy or uneven concrete will create weak zones that could lead to cracking or delamination.
  • The second batch of concrete should be the identical mix (but without glass or stone if used in the first mix).
  • It’s very important to use the same water content, and merely add more superplasticizer to make the second batch more workable.
  • It’s important to place the second batch before the first becomes hard or dries out.

For the gazebo job I did in Grand Cayman (8000 lbs of concrete), the extra price from using all white cement added up to only about an extra $100 in cost. Consider the need for 2 separate mixers, the extra labor and time needed to wrangle two mixes, and it’s easy to see that at times it’s simpler to bite the bullet and pay a bit more up front to make things simpler, and in the end, better and less expensive overall.

Here’s an example of a GFRC piece done with red outer shell (mist coat) and white core (backer). This was done just for illustration purposes. You can see in the second photo that some of the white showed through when the mist coat chipped.

gfrc red mist white backer

gfrc chip in mist coat

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

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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.

Making a tie-dyed concrete countertop

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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

colors

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 1 of 3

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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.)

Kool-Aid

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.

Types of integral pigments used in concrete countertops

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Concrete can be colored in a variety of ways, including using acid staining, dyes, colored aggregates, cement and integral pigments. This article explains the various types on integral pigments commonly used in concrete countertops.

Integral pigments are very finely ground inert particles that are mixed into concrete to change its color. Integral pigments can be dry powders or liquids, which really are liquid suspensions of solid particles (much like paint). Pigments are dosed like other admixture ingredients, based on the total cementitous material weight. Dosages can range from 0.1% to 10% (the maximum recommended dosage), but typically the range is narrower, from 0.5% to 5%.

Concrete is a harsh environment for pigments. It is wet, very alkaline and can be exposed to heat and ultraviolet light (from sunlight). This harsh environment can break down some pigments that cannot resist such attacks. This is why it is very important to use pigments designed for use in concrete. A vibrant blue pigment intended for the paint industry may not last long in concrete unless it can completely resist the concrete.

Pigments come in a wide range of colors.

  • Basic iron oxide pigments are the most widely used and are readily available, and they tend to be inexpensive. These are the basic “earth tone” colors: browns, reds, blacks and dirty yellows. Prices generally range from $2 to $6 per pound.
  • Special metal oxides provide other colors: some iron oxides are purply red, blue or yellow; chromium oxide is green, and titanium oxide is bright white. These are generally a bit more expensive, ranging from about $4 to $20 per pound, and true cobalt blue is much more expensive.
  • Synthetic pigments are generally even more expensive but provide the vibrant colors unobtainable from metal oxides. Brilliant violet, pure red and canary yellow are all available. Less expensive versions of expensive natural pigments (like cobalt blue) can make even some colors affordable. Synthetic pigments tend to be more powerful than iron oxides, so less is needed to get the full depth of color. Prices range from $20 to $75 per pound.

Pigments for concrete countertops

Powdered pigments are often sold in bags or cans, and can either be loose or granulated. Granulated pigments are marketed as “dustless” because the fine pigment particles are bound together with a water soluble binder. Granulated pigments are designed for use in mixer trucks where the coarse aggregate and lengthy, vigorous mixing action break the particles up. Some concrete countertop fabricators have noticed inefficient mixing and color streaking because the granules don’t completely break up.

Liquid pigments are solid pigment particles suspended in a liquid. The liquid helps to keep the pigment suspended for the duration of the measuring and dosing. Liquid pigments should be well mixed before dosing, because the pigment particles settle out. Pigment concentrations vary depending on the color or manufacturer.

Lastly, some pigments, especially some liquid and synthetic pigments, have water reducing or even superplasticizing characteristics. And some also have a mild retarding affect. It is important to try out a new pigment to see how it affects the concrete before using it for a paying client’s project.