Color Chart

A Guide To Help You Choose
The Right Color System for Your Project Written By Phillip J. Arnold Duplicate the color of granite and the texture of stone. Or create the effect of hand-fractured sandstone on a building and surround it with striking color-matched pavement. In fact, virtually any color, finish or texture is possible to achieve in a cost efficient manner with concrete. As a result, the popularity of colored concrete is on the rise and producers, designers, contractors and precast companies are faced with the problem of determining which method or combination is best for a particular job. This article is intended to serve as a guide. It compares five methods used to color concrete permanently: White and colored cements; color-conditioning admixtures; mineral oxide pigments; dry-shake color hardeners; and chemical stains. A few suggestions on ways to add interest finishes, textures, and or imprints are included as well.

Colored Cements

In addition to standard gray portland cement, there are four general types that affect color. The first is white portland cement, which is manufactured with minimum quantities of iron and manganese oxide to produce the white color. This type of cement is generally used for architectural concrete structures or in mortar, grout and cement paints. The second type if standard portland cement with a light tint. Usually the lighter than normal gray or slight tan shade is a natural result of the particular raw materials used in the manufacturing process. The third type is called special colored cement. Normally these cements are available in carious shade of tan. Some are relatively bright, but may lose some intensity with age. Finally, there is pigmented cement, which normally combines pigment with white portland cement. Color is reasonably consistent with colored cement because manufacturers of architectural cements maintain good levels of quality control. Colored cements are also easy to handle and batch when bulk storage is used. There are some disadvantages, however, when colored cement is compared to other methods. First, costs are dependent on availability and location to the job site. Second, the color range is limited and special shades are difficult to obtain with either white portland, standard portland with a light tint, or special colored cement. More colors are available in pigmented cements, but these are generally available on a special order basis only and are therefore more expensive. Also, special storage silos may be required at batching facilities unless the cement is handled in bags. Color variations may occur over a period of time as well, and they cannot be easily corrected.

Color-Conditioning Admixtures

Another method of achieving integral color is through the use of color-conditioning admixtures, pioneered by the efforts of the country's largest manufacturer of coloring and texturing materials for concrete, color-conditioning admixtures were specifically developed for use in ready-mix and precast concrete and offer distinctively improved performance over raw pigments. They consist of carefully proportioned compatible ingredients that are both milled and completely reground. This forms a homogeneous blend in which individual components including pigments can no longer be distinguished. They are set-controlling and water-reducing admixtures which meet the requirements a ASTM C 494, Specifications for Chemical Admixtures for Concrete. Color conditioning admixtures serve to increase concrete strength at all ages, improve workability, and disperse coloring and cement for excellent uniformity, placement and finishing characteristics. Color bleeding, laitance and efflorescence are also reduced. Since the manufacturer can modify formulations to compensate for drift in pigments and maintain strict ingredient and quality control, users can be assured of batch to batch color uniformity even over a period of years. Typically, for ease-of-use and foolproof control, color-conditioning admixtures are packaged in cubic-yard dosage units. Bag weight may vary with color and design-mix cement content, but dosing is always one sack per yard even for precasters using special mixes. Because color-conditioning admixtures are manufactured exclusively for use in concrete, specifiers and producers are assured of compatibility, stability, and fade resistance. And a virtual rainbow of colors is available. The major disadvantage of color-conditioning admixtures is cost, which can be as much as 80 percent greater than raw pigments. However, the reduced concrete rejection rate can more than offset the added expense. Keep in mind also that total cost will vary with slab or wall thickness and with the intensity and color desired. Color-conditioned concrete can be used for flatwork and vertical architectural concrete including hard rock and lightweight precast, glass fiber reinforced concrete (GFRC), tilt-up and cast-in-place construction. Placing and finishing techniques are essentially the same as those for uncolored concrete. Proper guidelines by the American Concrete Institute should be followed. Water/cement ratios should be kept low and constant. Proper curing, vibrating and finishing procedures must be followed. When used in conjunction with elastomeric formliners, color-conditioned concrete can simulate a wide range of textures, from split face rock to fractured fin and rough sawn cedar. The type III and white cements used in precast operations make possible even lighter or brighter colors than when grayer type II cement is used. And because formliners are reusable up to 50 times without a release agent, virtually any color/texture combination can be cost effectively crated. The possibilities are endless. For flatwork, trowel or room finishes, exposed aggregate and rock salt finishes are all possible. Because the color is integral, there is no limitation on the depth of a broom finish and exposed edges are automatically colored as well. Installed cost of pavement using these techniques is normally less expensive than stone, brick, pavers, or a printed concrete.

Mineral Oxide Pigments

Pigments are widely used in many industries including paints, plastics, pet foods (to make pet food look red, yellow or brown), and in construction products. Iron oxide pigments are the most common type and are either natural or synthetic. Natural oxides are mined and finely ground. They are normally the least expensive and are lowest in tinting strength. Synthetic oxides offer a full range of colors from full yellows to reds to blacks. Undertones, shade, and tinting strengths vary, but all are more intense than natural oxides. Costs for synthetic oxides are higher, but they offer a better value. There are three major manufacturers of iron oxide pigments, the Columbian Chemicals Mapico brand, Mobay's Bayferrox brand Pfizer. Distributors buy and resell pigments from these manufacturers. Since pigment colors may drift and exact dosing is difficult to control, pigments are most popular in the manufacturing of products where a slight color variation is acceptable. The largest users of pigments within the concrete industry are block, paver, and roof tile manufacturers. Results of raw pigment use by precast companies and ready-mix concrete companies have been mixed. In buildings and flatwork, the requirements for color uniformity and performance are much higher and any variation may result in the costly rejection of unacceptable elements. This often outweighs the cost advantage of using these products. Use of pigments, however, introduces the possibility of color streaking and variation due to problems in obtaining dispersion. And it may be difficult to match colors over time because of drifts in pigment color batches. Some pigments are not suitable for use in concrete as well. An example is ultra marine blue, which often disappears under attack from the alkali. Also be aware that pigments will decrease the ultimate strength of concrete by increasing its water demand. Pigments alone do not supply man of the extra ingredients that are highly desirable to obtain satisfactory colored concrete. And pigments are often field weighed for dosing which creates additional work and increases the risk of measurement error. As with color-conditioned concrete, mineral oxide pigments provide integral color. Finishing and texturing techniques and possibilities also are similar.

Dry-Shake Hardeners

Dry-shake color hardeners are ready-to-use products designed for coloring, hardening and finishing new concrete floors, patios, pool decks, walks, driveways and other horizontal surfaces. They also may be plastered on small vertical surfaces of freshly placed concrete incidental to flatwork, such as curbs, risers, and planters. However, they should not be used to plaster or stucco large vertical areas. Where heavy-duty wear and slip resistance in industrial or commercial floors, ramps, and loading docks are required, a hardener may be manufactured using emery aggregate instead of the normal silica. Metallic aggregates are also used for heavy-duty industrial floors, but they increase the possibility of floors becoming slippery, and rust may occur if moisture is present. Dry-shake color hardener should be a steak-free intergrind of pigments, surface conditioning and dispersing agents, and portland cement combined with graded aggregates are required. Intergrinding is important to avoid color streaking during finishing. Pigments used must be lime proof and have maximum resistance to the affects of sunlight. Aggregates are selected for hardness and purity and are carefully graded through a wide particle size range to give a dense wear-resistant surface. With dry-shake color hardeners, colors can be made more intense than with integrally colored concrete since they concentrate color at the surface. Very light pastel colors are achievable, as well, that would require the use of white cement throughout the entire slab if integral color were used. Also, except for blues, the cost of dry-shake color hardeners is relatively constant from color to color. Normally, for every 100-sq. ft., 60 lb. of hardener is used; for colors made with white cement, 100 lb. is used; and for heavy-duty applications, 120 lb. should be used. Dry-shake surfaces have several other advantages over integral coloring systems. Changes in the cement content of the concrete or slab thickness do not affect the cost of dry-shake systems as they do with integrally colored concrete. In addition, differences in the color of local cement do not affect the color of the finished surface. With dry-shake color hardeners, treated surfaces tend to be less porous because surface density is increased by the materials and the finishing techniques used. Another advantage is the ability to match the color of a main floor area in special heavy-duty sections, such as ramps or loading docks, by increasing the dosage or by substituting the corresponding heavy-duty material. All of the coloring methods mentioned in this article require proper installation techniques to achieve good results. However, the technique of applying a dry-shake material is basically different from placing other concrete. Some contractors lack the special skills necessary and attempt to finish too large an are at one time. This problem is compounded by the fact that the timing if finishing is more sensitive to temperature and humidity than if integrally colored concrete were used. Over troweling and trowel burns must be avoided. Proper curing is critical to achieve desired results and a color-matched wax curing compound is normally recommended. Also, avoid using dry-shake materials on toppings less than 2 in. thick because there will not be enough moisture to properly work in the hardener. Excellent finishing results can be obtained with either a trowel or broom finish, and with creative edging and scoring a very attractive and cost-effective surface texture and pattern can be created. Or, as an added touch, brick, stone or a variety of other designs can be imprinted into the concrete as part of the finishing process. The imprinting method, made popular by the Bomanite Corporation, has added a multitude of unique and interesting paving options from fish scale cobblestone to ashlar slate. In fact, the entire color-hardened paving surface can now be textured with a new generation of imprinting tools. The final result is both beautiful and structurally sound, as well as less expensive than conventional stone, tile, granite, or brick pavers.

Chemical Stains

Chemical stains differ from all the coloring materials discussed so far because they are applied to surfaces of cured concrete that are at least one month old and free from all foreign matter. True chemical stains are water solutions and metallic salts that penetrate and react with concrete to provide insoluble, abrasion-resistant color deposits in the pores of the concrete. They contain diluted acid to etch the concrete surface slightly and to remove any surface laitance so that the staining ingredients can penetrate deeper and react more uniformly. Concrete stain colors are limited by the chemicals used. Usually, black, green, reddish-brown and various shades of tan are available. The color is not merely a surface coating. The stain penetrates to a limited depth and will not chip, crack or peel. It can, however, wear away to the extent that the concrete surface does. In high traffic areas, it is a good idea to maintain stained concrete with periodic applications of colored wax or concrete sealers. Interesting and unusual applications have been made by applying stain to flagstone sculpture, board formed, and many other textured designs. Stains have enhanced specially formed concrete zoo displays, fountains, and other decorative projects. Exposed aggregate slabs, or panels can be stained without affecting the colors of most aggregates. Stains will not hide defects or discoloration in the concrete. Colors of the stained surfaces will vary in shade, as do natural rocks depending on porosity, age, and chemical composition of the concrete. The resulting patina effect is unique and cannot be duplicated with other coloring materials. For weathered or badly worn concrete, black or dark stains usually give the best results.

Advantages Over Colored Aggregates

These materials permanently color the matrix instead of relying on special colored aggregates. Using a proper mix design with a local standard aggregate and cement mix makes bidding more competitive because it is not necessary to stockpile special material. Also, if a structure or complex of structures is to be added to later, the colored concrete matrix will be more easily reproducible than if colored aggregates were used.

Selection

Selection of the method appropriate for a project requires careful consideration of a number of factors. Proper formwork, finishing and curing are as essential in obtaining good results as is the material involved. Once the exact system is selected, proprietary products which have shown satisfactory results should be specified. Too often, weak specifications allow inferior materials to be used, which can produce unacceptable results.

The Keys to Success

The results that can be achieved with colored concrete can be truly spectacular as long as a project is properly planned, and as long as proven products and experienced contractors are used. Do it right and freedom of design, a variety of possible finishes, cost-effective construction, structural integrity, and low maintenance can all be major benefits·benefits that illustrate why colored and textured concrete is becoming more and more popular.