Stamped concrete achieve exquisite masonry, wood or sculptured effects. The tool that makes the impression is used like a big cookie cutter on the plastic concrete surface. “Stamped concrete” is probably the most popular generic name for the result produced by the tool, although it may also be called patterned, embossed or imprinted concrete. A new star is born Where it’s used BY STEPHEN G. BOTTFELD PRESIDENT STAMPED CONCRETE IMPRESSIONS INC. SAN DIEGO, CALIFORNIA fter two decades of slow, steady growth, stamped concrete has suddenly become an overnight success. The idea started simply: Give customers the rustic beauty of masonry, plus the durability and low cost of concrete. The applications appeared limitless. The product’s growth quickened as architects, engineers, developers and contractors alike discovered its monetary appeal. Customers could save 40 to 70 percent on realistic brick, tile and cobblestone effects. Contractors could make up to 40 percent and more in profit. A star was born—as was an entire new market for the concrete contractor. Private surveys show that the contracting market for stamped concrete has more than quintupled in size in the last five years. Five new stamped concrete tool manufacturers have entered the industry in the past two years. Stamped concrete displays at this year’s World of Concrete drew unprecedented crowds. The response rate to recent advertisements in CONCRETE CONSTRUCTION magazine for stamped concrete products has been in the hundreds and thousands. New tooling that provides wood and sculpture appearances is now on the market. Other tooling systems are appearing—and disappearing. Suddenly, after twenty years, the entire construction industry had become aware of the beauty and benefits of stamped concrete. One marketing company’s estimate of industry size in 1978 was more than $155 million. Five years ago, the same company estimated the size of the industry at $25 million. This impressive recent growth has made many contractors ask important questions about stamped c o n c re t e. What follows should answer most of these questions. A What it is First, a definition. Stamped concrete is concrete, placed, colored and impressed with various patterns to * Numbers in parentheses refer to metric equivalents listed with this article. This method of patterning concrete can be used indoors or out, wherever you might use masonry, wood or sculpture on a horizontal surface (up to a 2:1 grade) . This means pool-decks and walkways—terraces and s h ow room floors—kitchens and shopping centers— highway medians, office floors and much more. The tools are even being used in tilt-up construction and in plant-cast wall panels. The stamped concrete look shows up eve ry w h e re. Busch Gardens; the Fontainebleau Hotel; Dallas, San Diego; Singapore; Dublin; Guatemala City—it is being specified and used all over the world. And it’s not confined to mild climates. The procedure has been used successfully in De n ve r, Chicago, New York, Vancouver, Minneapolis and Montana, to name but a few freezethaw areas. There are specifications in use that reduce or eliminate scaling or spalling. A wax coating keeps water from penetrating the slab, reducing the potential for freeze-thaw damage. In addition, the incised lines themselves act as control joints. Cracking, if it does occur, will generally follow the joint lines. This means that cracking in a stamped concrete slab is less noticeable than in a plain slab. What it costs One reason for the sudden popularity of stamped concrete is cost. It is a cost-effective alternative to p a ve r s, masonry and other similar products. And because it is cast monolithically—one continuous pour— many of the maintenance problems associated with those other products are reduced or eliminated. It is generally 40 to 70 percent less expensive to install stamped concrete than tile, cobblestone, brick, stone or sculpture. Of course, price and cost vary from area to area. The chart breaks down the costs for a 1700-square foot(1)* job completed in San Diego. By substituting your costs for those shown in the chart, you can get a realistic estimate of pricing in your own area. How much stamped concrete can be done in a day depends on the configuration of the slab, the number of tools to be used, the experience of the crew, weather conditions and other factors. The general rule of thumb is that with six tools, three finishers and one or two laborers a minimum of 1000 square feet(2) a day can be stamped. Depending upon conditions, the same crew with the same tools can achieve 3000 to 4000 square feet(3) or more in a single day. But, one note of caution: It is easy to become confused by “number of square feet per man-hour” figures because they fail to account for time spent in placing, finishing and coloring. How it’s done Methods vary slightly from one company to another, but virtually all stamped concrete processes use the same principles. Most major manufacturers publish suggested specifications for their processes, which meet or exceed ASTM materials standards. These specifications are intended to help architects, engineers, developers and contractors specify the exact pattern, color and effect they want for a job. First and most important, stamped concrete is concrete. It should be treated as such. Prepare the subgrade and place your forming, jointing and reinforcing materials (if required) just as you would for conventional conc re t e. Place and finish the concrete as you would normally. Spade, screed, edge and float. Color the concrete, using dry-shake pigments (or integral color), and float again. At this point, some manufacturers advocate placing 1- to 2-mil(4) p o l ye t h y l e n e sheeting over the colored concrete surface. This acts as a finisher when the tools are placed on top because the plastic is stretched, rounding the edges of the incised pattern; it also minimizes the possibility of sticking. Other manufacturers prefer a steel troweled (or fresno) finish and recommend placing the tools directly on the concrete surface. Because straight lines are important, a chalk line should be snapped across the surface to be stamped to square the tools. Once the first tool is squared, the other tools to be used are lined up and interlocked, and the stamping process begins. The tools themselves act as a bridge across the concrete surface upon which the finisher walks. If the concrete is fresh enough, a man’s weight will force the blades of the tool into the surface to the proper depth. As the concrete sets up, an impact tool may be used to drive the stamping tool into the concrete to keep the impressions even. If grouting is required (mortaring the joints such as in STAMPED CONCRETE COSTS a brick or tile pattern), the incised depth will usually reach 5⁄8 inch.(5) If no grouting is needed, generally no more than 1⁄4- to 3⁄8-inch(6) depth should be used. At this depth, the width of the joint still allows the concrete to be a good walk surface—even for women with high heels. If the area will be subjected to traffic, a light broom finish is generally specified for additional skidproofing. Before the job is considered finished, many manufacturers specify spraying a wax coating over the surface. The wax usually contains the same pigment as the surface color. It protects and brightens the finish. After the other trades have completed construction, another coat of wax may be applied and buffed to a high gloss, generally nonslippery shine. What mix to use Mix design depends upon the strength or durability required. Normally, stamped concrete is made with a 5to 6-bag(7) mix, using 3⁄8- to 3⁄4-inch(8) nonporous aggregate and placed at a 3- to 4-inch(9) slump. No matter what size aggregate is used, the concrete should be tamped (with a grate tamper) to get the rock down slightly below the s u rf a c e. Variations for each element in the mix design may be necessary because of differences in local soil, climate and job conditions. If necessary, mix designs can be radically changed. Concrete for stamping may be placed at high slumps; with 1⁄4-inch (10) aggregate; with fly ash extenders and with other changes. Such changes are not necessarily recommended, but can be made successfully. Any accelerator or retarder you wish may be used except for calcium chloride. It chemically reacts with color, causing premature fading. But be careful with retarders because they tend to set up the entire slab all at one time. Air entrainment can be used in the mix and is a must in freeze-thaw areas. But check your color supplier’s specifications first. Air entrainment creates body you can work with in the finishing steps. (a) THE JOB: 4-inch-thick unreinforced slab(b) 1700 square feet @ 2.50 SALE PRICE: $4250.00 MISCELLANEOUS MATERIAL $75.00 (a) Labor and material costs per San Diego, California, Labor costs include all union benefits. (b) Rough grading and forming not included. Final surface hand-finished. Some expansion joint material required. (c) Integral color. Dry-shake color would require 1100 pounds @ 19 cents. Total, $209.50. This design is called random stone. slab. Third, the wax protects the surface from traffic wear. And, fourth, the wax keeps the sun from fading the surface color. Wax should be applied as often as the area, weather conditions and other factors dictate. Some slabs, on the ground more than a decade, look fine without ever having been waxed. Some slabs are waxed every six months. Generally most slabs are waxed once after finishing and never again. Rewaxing should be done only if the customer wants to enhance the color. How to use color What effects are possible Most manufacturers, architects and specifiers think that stamped concrete surfaces look more attractive in color. It gives the impression an air of authenticity. It’s like the difference between color and black and white TV. Some contractors have managed to eliminate color by specifying special-colored sands in the concrete mix, but it’s not recommended. Two basic coloring techniques are being specified by most manufacturers. A third is in an experimental stage. Integral color is mineral pigment batched into the mix either at the ready-mix plant or in the truck mixer on site. The concrete is poured with the color mixed in. Dryshake color is a mixture of mineral pigment, sand, cement and additives. It is broadcast on the surface of freshly floated concrete, generally at a rate of 60 pounds per 100 square feet.(11) This usually produces about a 1⁄4inch(12) topping. Concrete stains are being used experimentally by several stamping tool manufacturers. To date only one manufacturer is specifying a stain. Stains alone generally don’t stand up to traffic. Most concrete stamping tools are versatile. The kind of impressions you can get depends on your tools, color, the concrete and your own know-how. For example, you can create a pillowed or rounded, slump-stone effect (for cobblestones), flat impressions with rolled edges (for tiles); or very flat impressions (for brick). You can stamp step treads and risers. You can use color and wax to create an aged or antiqued appearance. Methods for achieving these effects vary from manufacturer to manufacturer. There are four ways to judge the quality of finished work. First, are the impressions basically the same depth throughout the slab? Second, are the lines straight? Third, is the color work even and consistent? Finally, has the job been done according to specification and customer wishes? The answer to all four of these questions should be an unqualified yes. Finished view of European cobblestone pattern. Each coloring method has advantages and disadvantages. For example, dry-shake color is about one-third less expensive to use than integral color for a 4-inchthick(13) slab. Howe ve r, it increases the labor factor (although that labor would be tied up on the job in any event). Dry-shake color gives a harder surface. It also tends to stand up better in traffic, although some manufacturers report a chipping problem. Most manufacturers specify a colored wax for a variety of reasons. First, the pigment in the wax eliminates mottling. Second, the wax keeps water from penetrating the How to choose a system Generally, the successful manufacturers (whose contractor customers are also successful) are using a system comprised of stamping tools, hand tools, training, promotion, color, wax and more. Stamping tools vary in size from as little as 16 inches square(14) to as large as 5 feet(15) wide. The materials used to make the tools range from plastic and fiber glass to angle iron and cast aluminum. The most popular tools used in the industry today are cast aluminum. Tool features vary from manufacturer to manufacturer, but virtually all offer some sort of interlocking system that helps keep the tools on a straight line. Some tools, particularly small size and plastic ones, are meant for do-it-yourselfers. They are sold through building material supply houses. The larger tools are generally sold by the manufacturer’s captive sales force or direct from the manufacturer. Some are sold to customers on a franchise or licensing basis. The example earlier, describing one day’s production, specified six tools. Howe ve r, many manufacturers sell less than six tools per pattern. It’s easier to sell the tools that way. It allows a customer to “grow” into the market and build himself up to production strength. There are four major considerations when evaluating tools. • Is the blade of the tool deep enough and large enough to prevent the underside of the stamp from touching the concrete surface? If there isn’t enough draft to the blade, the impressions will always be slightly marred by the underside of the tool, particularly in wet concrete. • Is the technical backup offered by the firm selling the tools strong, consistent, reliable and recognized? • Are hand tools sold with the stamping tools? These are smaller implements used to finish an impression in spots larger tools can’t quite reach (such as near the edge of a wall). Some manufacturers provide hand tools which form a complete pattern (for example, a brick). There are arguments pro and con, but it is generally too easy to misalign with full pattern hand tools. Hand tools are available with a single blade that matches the blade of the larger stamp. They may be somewhat slower to use, but a mistake is likely to be less noticeable. • Fi n a l l y, is some form of training or user manual available? What to choose—franchise, license or purchase At this writing, there are two licensing companies and one franchising company in the industry. Their advantages are simple and strong: They provide exclusive territories, sales support, umbrella advertising and excellent training. Generally, their contractor customers do outstanding work. The disadvantages of these programs are nonrecoverable franchise or license fees, a royalty for work completed, and audits of a company’s books. These are some of the reasons why manufacturers of tools that sell them outright have been so successful. What the future holds The future of stamped concrete seems to hold unlimited opport u n i t i e s. We can’t see any economic development short of a depression which would slow its growth. The only negative possibility is that someone may develop a new product to replace it. But then, t h e y ’d probably have to wait twenty years for it to become a star. Metric equivalents (1) 160-square-meter (9) 75- to 100-millimeter (2) 90 square meters (10) 30-millimeter (3) 275 to 375 square meters (11) 290 kilograms per square meter (4) 0.025 to 0.05 millimeters (12) 5-millimeter (5) 15 millimeters (13) 100-millimeter-thick (6) 6- to 9-millimeter (14) 400 millimeters (7) 280 to 335 kilograms per cubic meter (15) 1.5 meters (8) 10- to 20-millimeter PUBLICATION #C790440 Copyright © 1979, The Aberdeen Group All rights reserved