Photo courtesy of Jon Nasvik, Cliffhangers, Inc., Hailey, Idaho.
More and more people are realizing concrete’s value for making countertops. Shapes of concrete countertops are only limited by imagination and the ability to build the forms. With the use of color pigments in combination with white cement and various aggregates, the spectrum of colors available in concrete countertops is virtually limitless.
It’s been more than a decade since concrete countertops found their way into shops, restaurants, and homes. Once the realm of either the do-it-yourselfer or the wealthy, they have gained acceptance in just about every level of residential application, from moderately priced homes to high-end palaces.
Whether an interior is traditional, contemporary, or somewhere between, concrete is a versatile medium to express the aesthetic of designer and owner.
Materials Used in Concrete Countertops
Coarse and fine aggregate account for the greatest proportions of concrete. Designers should choose aggregate carefully as it can impact the desired final look of the countertop. For example, coarse aggregate may be exposed by grinding or polishing, similar to terrazzo. When that is done, it’s important to get the right size, shape, and color of aggregate particle. From a color perspective, fine aggregate has a greater effect, at least on the mortar portion of the concrete mixture. Smaller particles have a tinting effect on concrete, so the sand can impart an overall hue to the finished surface.
Portland cement binders are the backbone of concrete. These materials glue all the other ingredients into a solid mass. Normal portland cements have a grayish color, although that varies somewhat from one source to another, and perhaps even from one batch to another. For darker colors and untinted concrete, gray portland cements are the easiest choice.
For white or lighter colored surfaces, white portland cement is available. It provides a base that is easily colored with pigments, stains, tints, or dyes. It is a type of portland cement and has the same behavior as its gray counterpart. Here again, sand can play an important role. When mixed with white cement, sand particles impart an overall color to the concrete. If pure white colors are desired, white sand should be used. For other colors, sand should be compatible with the intended color.
Concrete pigments come in various forms. For integral coloring, many are based on synthetic mineral oxides for their durability and consistent quality. The liquid versions are the easiest to use because they disperse readily when mixed into the fresh concrete. Powder versions have a long history of use, however, and give excellent results.
Post-applied color is achievable with stains, tints, or dyes. The basic types of materials are chemically reactive stains and water or solvent-based dyes and tints.
Chemical stains are water-based acidic solutions. They contain metallic salts that react with calcium hydroxide in the paste to produce insoluble colored compounds of blue-green, black, brown, or gold. The stain reacts with the concrete with a degree of variation, and can result in a non-uniform effect. They can be used on old or new concrete. Stain also reacts with calcium-based aggregates such as limestone. Stains should be avoided with lean concrete mixtures with low cement content. Prior to staining, concrete should age at least 14 days; blue, green, and gold colors require 30 to 60 days of curing.
Dyes and tints do not react chemically with concrete. They often produce colors that are not available in chemically reactive stains, namely the reds and yellows. They help intensify colors when used in successive applications or can soften or even out the appearance of slabs that have been chemically stained. They are water or solvent-based materials and must be applied to concrete that accepts penetration of materials. The slab should be treated with a degreaser and a mineral acid solution to reach a surface pH of about seven or eight days before dyes and tints are applied. A sealer helps protect the color.
Some manufacturers formulate waxes to work with many of the colored concrete finishes. They can heighten the slab’s color but would have to be deemed safe for food. They improve concrete appearance and help a colored slab retain that appearance, but require periodic reapplication.
In the past, recommendations were to do periodic maintenance on concrete countertops, but the newer sealers have lessened the need for this activity. One of the most important considerations regarding sealers is the finish. Much like everyday paints, sealers come in glossy, satin, matte, or flat finishes. This aspect of surface treatment has a big impact on the countertop’s appearance. The decision should be made with regard to planned lighting for the space. An article by the Concrete Countertop Institute gives a detailed description of the types available and a comparison of their performance characteristics.
Inlays and Imprints
Countertop designers have experimented with various techniques to add interest to surfaces. Inlaid materials include shells, fossils, metal objects and scraps, natural stone, tiles, and other varied pieces. The long-term durability of the inlay should be considered when choosing it, although a sealer will normally provide some additional protection.
Imprints sometimes work in countertops, but shouldn’t be so deep that they pose a collection area for solids or liquids.
The most common finish on concrete countertops is a hard steel troweled surface. Not only does this densify the skin, it smoothes out the surface so that it is safe for anything that might be placed on it.
Sinks in homes are kitchen necessities but ones that can add interest to countertops. The sink can be concrete, either integrally cast with the countertop or a separate casting, or it can be metal, porcelain, or composite.
Concrete Countertops: Design, Forms, and Finishes for the New Kitchen and Bath (LT266)
This handsome, lavishly illustrated book is the first on the subject of concrete countertops, which have enjoyed rising popularity in recent years. Written by California designer Fu-Tung Cheng, it provides detailed instructions to homeowners and do-it-yourselfers for designing, mixing, pouring, forming, coloring, troweling, in-laying, and finishing decorative concrete countertops. The book showcases concrete's limitless aesthetic versatility-its ability to mimic marble, glass, granite, and other materials-along with its proven advantages of strength and durability. Published by Taunton Press, publishers of Fine Homebuilding magazine.
Concrete at Home (LT288)
Master designer Fu-Tung Cheng leads you on a tour of the most beautiful concrete design possibilities in Concrete at Home. Using rich photographic illustrations and clear and comprehensive text, the book provides fabrication techniques used by the author as he creates a series of beautiful architectural elements that includes floors, walls, columns, fireplaces, and countertops.