Decorative Concrete Institute

Decorative Concrete Institute

Bob Harris

Consulting • Education • Installation • Training

Fancy Flatwork

Concrete never looked so good

By Bob Harris

A basic understanding of working with concrete and color is important -- but so is having the right tools.

Anyone who's ever grunted a slab into place might have trouble believing that concrete flatwork could become an architectural trend. But it has. The cost-effective finishes you can produce through patterned, stained, and textured decorative concrete are limitless. And while the tools aren't exactly exotic, the techniques and timing are crucial to success.

The basic products used to create decorative concrete include texturing tools, which are mat-type imprinting tools for texturing freshly placed concrete: admixture, which is color added directly into the ready-mix: color hardener, which is a dry-shake colored powder broadcast over wet concrete: and chemical stains, which are liquid penetrating stains that combine with Cured concrete to produce permanent variegated or translucent color effects.

A basic understanding of working with concrete and color is important-but so is having the right tools. Having enough of them and understanding how and when to use them is critical.

Concrete Finishes

Planning and timing are the keys to successful concrete finishes. From the original pour to the final touches, concrete goes through a lot of stages, including the curing process. Different tools correspond to different stages of the hardening process, so you need to understand good concreting techniques. And you need to provide plenty of tools to work the concrete and enough workers to operate them.

Floats

On a fresh pour, the float is the most important tool. Using the proper type of float and floating technique to distribute the wet concrete affects the long-term durability and quality of the material. Don't rush the finish. Premature surface finishing will result in a low-quality surface that won't stand up over time. Always use a wood bull float when the concrete does not include an air-entraining admixture. If the mix does have an air-entraining admixture in it-which means you have to use a magnesium bull float-try to keep your float as flat as possible on the surface.
The objective of floating is to keep the surface open: that allows the bleed water to evaporate. It you aren't careful floating the surface. you can make the surface too smooth by float-ing the bleed water into it, and it won't cure properly. This concept also applies to hand floats.

You can worry about making, a smooth surface later in the curing process, when you trowel it to a final finish.

Hand Tools

Many decorative projects include accent bands in contrasting colors, which require the use of smaller hand tools to conform to the size of the band. The most efficient way to make an accent band is to use what is commonly called a combination tool. This tool simultaneously bevels the perimeter edge and creates a groove for the hand border. Keep in mind that the combination tool conforms to the lines of your perimeter forms and your band-lines will only be a, straight as the forms.

Once you have evenly floated the concrete. leaving no dents or holes. you can add the color and start working on other decorative elements. Having hand floats and finishing tools ready in a variety of sizes will make your job easier -when finishing the bands or other design elements. Allot enough trowels and other tools for each color, especially when working with different surface colors, or color hardeners. Color hardeners are hand-broadcast over the surface of the wet concrete and must be evenly troweled into the concrete.

Imprinting Tools

Imprinting takes place when the concrete is well into the hardening process, but still impressionable enough to take the imprint. As a rule, you should allow' for enough imprinting tools to span the length or width of the project plus one additional tool. The additional tool is sometimes called the stack tool; it starts the second row. Having too many tools is better than not having enough. A sufficient number helps ensure that the entire Stamping process is Successful. Use good quality imprinting tools that will support your weight so you du not create "bird baths:' or imperfections, in the pattern.

My set of imprinting tools includes a flexible tool called a floppy. The floppy has the same pattern as the platform style tools but is made of much softer polyurethane. enabling it to bend and conform to surface variations. Floppies come in handy when imprinting three-dimensional surfaces, such as stairs, or any odd leftover areas not quite covered by the Imprinting tools.

Another decorative option is to use texturing skins. These are flexible pieces of polyurethane that come in different shapes and sizes. They don't have lines or grout joints, so they only impart texture, allowing for a more free-flowing pattern. It's a good idea to include a tamping device in your toolbox to tamp the imprinting tools as the concrete hardens--although your weight is usually enough to transfer the pattern.

Also, keep an assortment of chisel sizes handy to touch up the tooling of the patterned joints. Especially with troweled-in color hardeners in small areas, such as bands, the joints often get blurred. And once you have troweled in any desired colors, check all joints and your edging to make sure you maintain clean lines.

Staining Tools

Staining is also gaining popularity as a flatwork finish. Chemical stains can be applied to pre-existing concrete as well as on freshly cured surfaces. Some people work with stains as an overall color application, while others work with them almost like paints, creating very detailed and intricate designs. You can even make stains that mimic marble floors.

Almost anything can be used as a staining tool, from spray bottles to sea sponges to Saran Wrap. I've even seen a designer pour the stain onto the dried concrete and blow the color in random branch-like patterns with air. Whatever design tool you choose, it is important to keep in mind that stain is very caustic and should not come into direct contact with your skin.

Design Tools

Another popular decorative technique is installing sandblasting templates on new or old concrete. The company 3M makes self-adhesive template products. Their materials can be cut into intricate patterns and borders and applied to the cured concrete. Whatever area is covered by the material is protected from the sandblasting, leaving a smooth-troweled surface. The unprotected area is etched by the sand. The resulting texture can range from very fine to coarse, depending on the depth and texture specified by the design.

Saw-cutting is commonly used to cut joints into cured concrete, but many designers are also using saw-cutting as a design tool. When cutting aesthetic joints, or creating the look of tiles, always mark the concrete first with a chalkline. A walk-behind saw-cutter is the easiest way to cut large, straight lines.

For freehand forms I suggest a 4-inch handheld grinder with a 1/8-inch to 1/4-inch-wide diamond-tipped blade. You can sketch the design in pencil for guidelines, but you really need to be a very accomplished saw-cutter to go freehand. The Dremel is another popular tool for adding intricate detail to designs.

Tips for Interiors

Decorative concrete flooring has become very popular for interiors, from floors to countertops. The tools are essentially the same for interior and exterior applications, except for one important difference: Interior equipment should be dustless. Especially with saw-cutting and sandblasting, there are specific attachments or models for dustless interior work.

Familiarity with the various tools-and knowing how to use them correctly-is paramount to the success of an architectural concrete project. Don't forget: Good planning helps ensure a good outcome. Concrete is a dynamic building material-it won't wait for you to run to the hardware store to purchase some additional trowels and chisels.

Bob Harris is the director of product training for the L.M. Scofield Co. He has 18-plus years of experience in the construction industry and has completed a three-year apprenticeship program for cement masons.