Article No: 176

2006-05-03 10:24:16
Decorative Concrete
By: Cindy Rizzo with Jan Bloom


Finishing the slab of a ground floor or basement is a popular choice. The simple method of broom finishing and saw cutting provides a striking appearance which complements contemporary, modern or traditional décor. Inset: A simple broom-and-band finish.

No matter the size of the budget for a project, it is human nature to want the best value for every dollar spent. Decorative concrete paving provides an economical alternative to more costly materials for those who know how to finish this versatile material to look more expensive than it really is.

Without purchasing additional equipment or learning complicated techniques, contractors can create beautiful decorative concrete finishes without significantly adding to the budget. Savvy contractors use the tools they already have to add finishes and textures to integrally colored concrete--details that can look great without more labor-intensive stamping or stenciling. Alternatively, stamping and stenciling can be used in limited areas alongside some of the techniques described here. Not only do these solutions offer the customer a beautiful look that's far superior to plain gray concrete, the contractors can make a slightly higher profit on each project.

Broomed concrete
One of the simplest methods for adding texture to integrally colored concrete is accomplished with a broom. Not only is "broomed" concrete more slip-resistant, it's a handsome look that is the simplest to create. Working when the concrete reaches different levels of dryness, the same broom can be used to create many finishes and patterns. Stiff-bristled brooms can produce light, medium and heavy finishes.

Attractive and uncomplicated fish scale patterns can be installed with a broom. To create a fish scale pattern, the concrete finisher simply takes the broom and pivots around an area to create a semicircle in the concrete, then moves to the next area and repeats the process consistently. As the installer moves across the slab, the next semicircle is placed on top of the previous row. The end result is an attractive, slip-resistant surface.

Use a trowel to change the surface color
Basic though they are, trowels are one of the most versatile tools concrete finishers carry. A trowel or a float can be used to swirl, smooth or sweat the concrete. These finishing techniques change the surface color and add a pattern and texture. The contractor uses the trowel or float to make a swirled imprint or another type of arc on the surface. This finishing technique is repeated consistently until the surface is fully patterned. Depending on the tool used, the finisher can create a coarse, medium or smooth textured pattern. Aluminum floats and steel trowels both create medium or smooth finishes.

Another technique uses a swirl float. A rubber or wood float is used to make swirls in the surface. When the surface is floated, it brings up the sand. Sandier surfaces offer an almost uniform finish. Windowpane or other box-shaped patterns require only a bit more labor. To create them, the installer begins by lightly broom finishing the surface of the concrete. Then the finisher goes back over the surface with a steel edger or groover to smooth the edges and to create borders and square areas.

A slightly more complex treatment is a sweat finish. Creating this type of texture involves using a magnesium float and running it lightly across the top of the surface to give it a wrinkled appearance. Even though a smooth float is used, this method creates a wrinkled effect that, depending on freeze/thaw issues, might be an acceptable non-skid finish.

Exposed aggregate: a visually exciting alternative
Exposed aggregate is a type of decorative concrete finishing that's great for patios, walks and driveways because areas where the rocks are exposed are rougher and slip-resistant. This technique exposes the smooth stones and pebbles that are part of the concrete matrix. The selection of aggregate sizes and colors can be chosen to reveal random patterns and colors. Alternating the finishing technique between fields of exposed aggregate with broom-finished segments adds variation.
Creating exposed aggregate surfaces can be accomplished with several techniques. The most basic method involves applying a surface retardant to slow the pace at which the concrete cures at the surface. After the retardant has been applied, the installer takes a water hose and washes the surface away to reveal the underlying aggregates that are embedded in the hardened substrate below.

Another popular method is to broadcast or "seed" the surface with a second type of aggregate so that the top surface has one color and type of aggregate and the underlying concrete has another. This technique requires an additional installation step. However, the concrete is placed and bull-floated as usual. Then, the decorative aggregate is broadcast into the surface and bull-floated again. The contractor applies the surface retardant and returns the next day to wash the surface and expose the aggregate that was seeded.

Add visual interest with sandblasting
Sandblasting is another way to create a decorative finish. The most basic type of decorative sandblasting involves removing a very small portion of the surface in order to change its color. Often used to delineate borders and create fields of varied colors and textures, sandblasting retextures the surface at a much shallower level than exposed aggregate. The result is a smooth surface similar to unpolished granite.

Sandblasting borders or fields that create a pattern is a technique often used on driveways, patios and walkways. Adjacent areas must be protected and parts of the concrete that won't be sandblasted must be carefully masked and protected. Also, recently installed concrete cannot be sandblasted until it has cured fully--about 28 days after installation. Many cementitious toppings cure more quickly and can be sandblasted sooner.

Another look that's becoming popular inside homes is sandblasting kitchen, bath and recreation-room flooring, and it's a fraction of the cost of installing natural stone. This can create the handsome appearance of granite tiles. Contractors use expansion joints as decorative joints--joints placed for their appearance within the room.

More complicated sandblasted designs involve stencils. Many standard stencil designs are used to create border effects and are available ready-made. Stencil patterns are cut into resilient, self-adhesive sandblast-specific materials that are applied directly to the substrate surface. Some custom stencils are also available.

Contractors work with these stencils in several ways. Sometimes they pour the concrete, apply a color hardener, seal the concrete surface and then sandblast the design. Then, the design can be left as it is or colored with concrete stain. Another option is to pour and seal a plain gray concrete surface, sandblast the design into it, and then chemically stain the sandblasted area to add more contrast.

Next up the ladder in cost and complexity are accent graphics, such as logos or crests. Most often seen in commercial businesses and municipalities, some people are so enthusiastic about this uniquely personal look that they have a family crest sandblasted into the dining room or entranceway of their home. These custom stencils can be created with virtually any level of intricacy.

Decorative scoring
Last, but certainly not least in the contractor's bag of tricks, decorative scoring is another way to create visually interesting decorative concrete surfaces. With this technique, the contractor creates a pattern by placing joints just for their appearance. Obviously, some joints are required to prevent cracking caused by expansion and contraction. By adding to those, one can create a more interesting and varied appearance while disguising the necessary joints at the same time. If the joints are grouted, a concrete floor can look like inlaid marble, tile or stone.

The most important step in selecting any of these finishes and techniques involves having the concrete contractor produce a job-site sample--using the colors, materials and finishes proposed--for approval.

These are just a few of the numerous ways concrete contractors can use the tools they already have to create many different decorative concrete finishes cost-effectively. These techniques not only allow contractors to offer their customers high-end style on a moderate budget, they also provide a unique appearance that adds to the property value.