The role of concrete
"There is nothing more beautiful than concrete that has been aged," said waterscape designer David Tisherman, of David Tisherman's Visuals Inc., Manhattan Beach, Calif. "It is one of the most versatile materials I've ever worked with." Concrete is a cost-effective structural material for flat applications such as pool decks and patios. Concrete can also be poured in place to create three-dimensional shapes, including furniture and monolithic wall formation, but these applications can be very costly.
So how can contractors add value to concrete at either end of the spectrum? By adding color, texture and dimension. One of the advantages of concrete is that a single material can be used to achieve a variety of looks throughout the installation. Decorative concrete can be used with carefully planned plantings to tie together various spaces and features, from a swimming pool or hot tub to a waterfall or fountain, a garden walkway or patio, even a driveway; and coordinate them all with the color and appearance of the house.
Techniques
Textured concrete forms the basis for decorative concrete in pool decks and spa areas. It is especially effective with colored concrete, as described below. Imprinting can replicate the look of natural stone, either with embossing skins that leave a continuous pattern or with platform imprinting tools that create the look of individual stones or tiles. Other imprinting patterns look like wood or bricks. Tisherman also likes simple steel trowel, exposed fan and board-formed concrete finishes for a contemporary look. Varying textures throughout a project adds interest and helps define different outdoor areas.
Texturing works with various coloring techniques. Integral color is dispersed through the whole slab and the finished translucent color has the appearance of depth. True coloring admixtures, unlike raw pigments, are streak-free, UV-stable and non-fading.
Dry-shake color hardeners hand- broadcast and troweled into the surface of freshly placed concrete offer more opaque, vivid colors than integral color. They also improve durability and increase resistance to freeze-thaw cycles.
More complex color effects are added to both integrally-colored and color-hardened concrete when imprinting tools are used. These tools require a release agent to allow the imprinting tool to be lifted without pulling up the cement paste. Colored, powdered "antiquing" release agents add a color or multiple colors to a project. These colors complement the color of the concrete and add to a natural, dimensional look.
Chemically reactive stains are less commonly used outdoors, but their unique interaction with the materials in the concrete creates one-of-a-kind, natural-looking effects. Stains can only be applied after the concrete is fully cured. Stains can be used to dramatic effect by hand-applying them to just a few elements, stones or tiles in an imprinted pattern.
All of these texturing and coloring techniques can be applied to old, worn, outdated concrete through the use of cementitious toppings. These are available in different grades suitable for imprinting, stenciling or broom finishing. They are applied in a base color and additional color can be applied with antiquing release agents or stain. Cementitious toppings are particularly useful for remodel jobs - the same topping can be applied to the old concrete and the new addition to create a seamless transition between the two.
A note about color selection: dark colors result in a hotter surface, so they should be used where landscaping or structures provide some shade. Dark colors also show contaminants like pollen or chlorine residue and so need to be cleaned more often.
Finally, to get the full design benefit of decorative concrete it must be properly cured and sealed. Air curing can result in mottled or inconsistent color. Use a color matched curing membrane or curing and sealing compound to get true, consistent color. For a more varied, less uniform look, a clear curing and sealing compound may be used. Sealing decorative concrete protects the pattern and color from damage and wear, not to mention spills and stains. The sealer should be reapplied as necessary.
Pointers for pool decks
The basics of good decorative concrete placement apply to pool decks - good surface preparation, careful installation and proper curing and sealing. In addition, there are some special considerations.
One important difference between pool decks and other concrete installations is the near-constant presence of water. The more porous the finished surface, the easier it is for water to infiltrate and cause freeze-thaw damage and mold growth. Concrete colored with dry-shake hardeners is less porous than uncolored concrete, but all decorative concrete should be sealed. A professional-grade polyurethane joint sealant should be applied to the saw cuts and joints to help prevent water infiltration. Sealing joints is equally important for cementitious toppings, where water infiltration can interfere with the bond of the material and cause delamination.
Water poses a safety hazard as well. Pool decks require a slip-resistant surface. For flat concrete, McMahon recommends a broomed finish. For imprinted concrete, he adds a slip resistant additive to the sealer for extra traction.
Pool decks, unlike walkways or driveways, require a three-dimensional edge. This could be a coping cantilevered out over the edge of the pool. Natural stone can be used for an edge, or a border can be textured into the concrete to mark a clear line between the pool and the deck. Sometimes a pool has a negative edge, where water flows over to give the appearance of no edge at all.
Pool decks may include apparatus not common to other concrete installations - bonding wires, diving board stands or railings. McMahon recommends taking special care to learn to install these properly.
Finally, as we all know, concrete cracks. Proper design and site preparation, as well as correct mixing of materials and use of tools, can keep cracking to a minimum. Make sure the ground is properly compacted, especially where a ramp was used to excavate a new pool. Uneven settling will cause structural cracks. Control joints to direct or minimize cracks can be incorporated into an imprinted pattern by cutting along the grout lines. Joints or cracks in existing concrete must be reflected in a cementitious topping. Beyond these precautions, cracks must be accepted as a fact of life. Tisherman believes that hairline cracks add to the richness and texture of the concrete. "Aged concrete looks more elegant, more romantic. The imperfections make it more personal." After all, something unique and personal is what homeowners want from their backyard oases.
Training, training, training
It should be clear by now that installing pool decks that meet today's aesthetic standards requires well-developed skills and careful, patient work. Homeowners need to understand that while concrete is a cost-effective, versatile material, the success of the project depends on paying for a proper design and installation.
Truly beautiful results come from a homeowner-designer-contractor team - a homeowner who understands the capabilities and limitations of concrete, a designer who can interpret the homeowner's wishes and give clear direction, and a contractor skilled and experienced enough to execute the job at a high professional level.
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