Everybody has an idea of what concrete is - hard, gray, cold. That's been changing for the last decade though as more and more people experiment with concrete as a decorative element in homes and businesses. Some areas of the country have already seen some of these finishes but here in the hinterlands of Washington and Idaho, they're fresh and exciting.
Through the use of stains and colored pigments, stamps, textured patterns, ornate sawcuts, epoxy overlay, and more, the concrete elements of homes and commercial buildings concrete are becoming increasingly attractive. Let's take a look at a few techiniques....
Exposed Aggregate
One of the most popular and enduring decorative concrete finishes, exposed aggregate uses the texture of the rock or stone in the concrete to embellish the surface. This is actually not new - look at older buildings and you'll see examples of exposed aggregate in floors and walkways. The difference is in the prevelance. It's is now being done as a cost-effective way to add texture and color to grayscapes.
In this technique, concrete is placed and floated as normal. The concrete is left to set and the surface paste is later removed by washing and/or brushing. In a variation of the method, select aggregate is cast over the fresh surface and embedded prior to setting of the concrete. Washing and brushing follow as before to remove the mortar from the surface, fully exposing the natural color and texture of the aggregate.
The most interesting additive I've seen wasn't an actual aggregate (stone) that was exposed. The architect has specified crushed blue glass to be embedded. The effect was spectacular but the concrete finishers absolutely hated working the glass.
Stamping
Stamping, done for both interior and exterior concrete surfaces, has made a big impression over the last several decades. Stamped surfaces are created by literally imprinting designs on fresh concrete with patterned or textured mats and templates. Having started as simple shapes and minimal textures, stamping tools and techniques have continually evolved to an advanced stage. current stamp templates mimick natural stone, rock, wood, brick, and more.
Standard procedures for placing, finishing, and curing concrete flatwork apply - with a few added steps. Using a stamping tool or pattern, fresh concrete is imprinted after the initial float pass and application of a release agent. If color is to be used, a dry shake color harder may be applied during finishing. The stamping procedure effectively replaces steel troweling, and the effect is a unique surface in both pattern and texture.
There are many ways to color concrete-before it has hardened or afterwards. Integral pigments are mixed into fresh concrete to create through-body color. Alternately, stains, tints, or dyes can be applied to hardened surfaces to impart color. Chemical stains react with hardened concrete to become an integral component of the floor surface. Pigmented tints or dyes deposit finely ground pigments into the substrate. To allow for the greatest range of colors, including pastels and deep, vibrant hues, white portland cement provides a neutral tinting base for adding color. Alternately, it enables bright white finishes when used in combination with white aggregates.
Stains enhance the inherent irregularities in the concrete surface with color to resemble a marble appearance.
Stained Concrete
Chemically reactive stains are water-based, acidic solutions that contain metallic salts. These metallic salts react chemically with calcium hydroxide compounds (hydrated lime) in hardened concrete. Such reactions form the insoluble colors that become a permanent fixture of the hardened concrete surface.
Partly due to the irregularity in finishing patterns and partly due to the inherent variation of the concrete materials, stain chemicals react in a very irregular pattern - giving it a decorative effect. As a result, mix constituents and finishing techniques will greatly influence how effective the staining can be. Controlling these parameters is important for achieving the best effect from the stain.
Stains can be applied to old or new concrete; to colored or gray surfaces; and may be used in conjunction with other decorative techniques and creative joint patterns. To protect and enhance the color of the floor, using a sealer is an important step. However, just as material selection for the concrete is important, selection of the appropriate sealer is also important for the performance and durability of the floor.
Jointing/Joint Patterns
Sawcut joints are installed using either an early-entry saw after concrete finishing or a conventional saw after concrete setting. Alternately, jointing tools (rather than saws) can add pattern lines to fresh concrete surfaces. Since joints should be used to control concrete cracking anyway, this is a simple-and purposeful-method for adding greater interest to concrete surfaces.
Painting
Using stencils and paint, the concrete slab becomes the artist's canvas. Some designs are very detailed and intricate and require etching tools to create fine lines.
Artists at World of Concrete in Las Vegas demonstrate their abilities of transferring elaborate drawings onto concrete slab surfaces.
Architectural Pervious Concrete
In today's environmentally conscious climate, the benefits of pervious concrete to sustainability have reinvigorated interest in these free-draining pavements. But, although it's appealing for its technical benefits, pervious concrete hasn't necessarily been attractive...until now. Renewed attention to pervious pavements has led some people to experiment with improvement of the surface aesthetics-and spawned a new type of concrete sometimes referred to as "architectural pervious concrete" (APC).
Most pervious concrete has a sort of popcorn look about it: Uniformly sized aggregate, falling within a narrow aggregate gradation, leads to a concrete with open void areas that promote fast drainage of large volumes of water. Some like the organic, rough-textured look of plain pervious concrete. But for those who want a different look, there are several options for enhancing the aesthetics.
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