Carefully installed, vertical retaining walls may be constructed using segmental retaining wall units. On the base of a 6" thick leveling pad, modular concrete facing units are stacked with reinforced backfill, 12" thick drainage fill, and geosynthetic reinforcement.
	Contractors need to provide external and internal drainage to protect the retaining wall structure. This interlocking retaining wall system drains naturally, so no weep holes are needed. The surface drainage can be diverted with a plastic soil cap or formed swale. At the base, an embankment drain, can also be used to stop flow into the soil. Then, in order to offset the effects of rising ground water, contractors are advised to install a drain zone/overflow pipe beneath the pad.
	When installing the formwork for stenciled concrete, prepare the concrete slab on-grade with a thickness of 4" or greater (right). The formwork may also be installed as a 1/2" or thicker topping over a base slab.
	Poured-in-place concrete slabs usually contain construction joints, control joints, and in certain cases, expansion joints. Paving distributors can advise on how to best install such joints on each specific project to minimize the possibilities of cracking.

From famous walls like the Great Wall of China and the Berlin Wall to famous paving systems like the fabled Yellow Brick Road and the renowned Route 66 and Appian Way, walls and paving systems have graced our lands throughout history. Most importantly, walls not only define property or act as a security barrier, but also retain soil, allowing cities to build and expand; pavements allow transportation by vehicles or walking. Today, a variety of intricate designs and challenging installations offer Landscape Contractors an opportunity to specialize--even build a business niche--in the mastery of walls and paving systems.

Generally, pavements are classified by their intended use within a particular landscape or design context. Paving materials include various textures and colors that line an entryway to a residential project, create streets and sidewalks, or accentuate a patio or pool area. Today, there are many decorative paving options that Landscape Contractors must be familiar with, including stone, concrete, asphalt, brick or wood. In fact, specific materials such as concrete or asphalt can also be designed to look like others (such as brick or wood). In addition, retaining devices not only include concrete or block wall structures, but also embankment reinforcing structures such as rip-rap stone, fiber matting, and highly fibrous rooted plants. These structures, regardless of material or shape, must be constructed to withstand earth pressures, and other structural failure, such as vehicle loading, highway vibration and effects of extreme moisture conditions--like heaving due to swelling and frost/thaw cycles.

Contractors who choose to specialize in walls and paving systems not only need to become familiar with many varieties of products and material, but also develop a strong working relationship with their local distributors. These companies can provide invaluable technical support and service to both contractors working in the field and those responsible for maintaining a site. For example, Mike Price, Bay Area Concrete Director of Sales and Marketing and a distributor of Bomanite concrete paving systems, provides on-site construction support for Landscape Contractors; once the contract is secure, a representative from his company will go out to the site with the contractor to shoot the grades. After the installation, his company will return 6 to 12 months later to clean, pressure-wash, and apply acrylic coating to the slab. As for Bill Braun at Crystalite Corp., a distributor of Rock-wood Retaining Walls, "In addition, on-site product and technical support is offered in our regional area, and installation guides are provided free of charge." Beyond on-site support, local distributors can provide Landscape Contractors with valuable "tips of the trade."

For example, when installing patterned or imprinted concrete, Price advises Landscape Contractors to "Seek out an experienced concrete contractor licensed by an imprinting organization. Make sure you also get a quality guarantee for one to five years."

According to Garrett E. Pack, general manager of the Santa Ana, CA- based Mark Company--a distributor of StreetPrint Pavement Texturing--Landscape Contractors "should be aware of the significant cost advantage that imprinted concrete has in decorative entries to projects and crosswalks as well as other applications." He adds, "In some parts of the country, the product has an additional technical advantage in that it is a flexible pavement material. Concrete products, for example, in climates that are subjected to extensive freeze/thaw cycles, tend to break and crack; an asphalt pavement resists that process much better."

William Candee, President of William Candee Enterprises, Inc., distributors of Buechel Stone Corp., explains, "Natural stone ages and becomes more beautiful, whereas concrete products normally look their best at installation. Each project will vary because of the natural variation in the stone (no two projects will look alike.)" Therefore, contractors should be aware of the intricacies of working with natural stone. Experience alone represents a "tool of the trade; the more you do the better you know."

Ted Corvey of Pine Hall Brick explains, "In the United States, brick and interlocking pavers are now beginning to be recognized as a form of pavement for heavy traffic; generally in the past they have been used as a form of decorative paving." Landscape Contractors have an opportunity to work with the mechanics and structural challenges of brick and interlocking pavers, as more and more specifications call for these products. However, contractors need to be aware of the fact that the loss of the joint sand in interlocking clay or concrete paving is known to be one of the main causes of failure in this pavement type. Sealers have been used in conjunction with the pavers to enhance the aesthetic appeal in high profile areas, then as a means to ensure the structural integrity. Problems have been experienced, however, in some installations because of the build-up of efflorescence under the sealers, particularly when the pavers are subjected to water. This difficulty causes the appearance of dirty white or gray deposits, and builds up a hazing on the surface that is very difficult to remove. As a result, installers may shy away from using sealers simply to avoid these problems.

Recently, a new water-based joint stabilizing penetrating sealer has been developed by Surebond Inc. called SB1300 (See Set In Concrete on page 10). An easy to-apply-product, it dries in minutes and cures in the joint sand to form a tough, elastomeric compound that literally glues the pavers together. According to Peter Van Niekerk, President of Surebond California, Inc., this sealer is applied to the pavement by means of a low-pressure sprayer and the excess is drawn off and concentrated in the joints using a rubber floor squeegee-- thereby "wiping away" the obstacles facing the installation of interlocking pavers and sealant.

Other paving accessories available to contractors include paving restraints, which are intended for areas where hardform and natural landscape meet. These areas are usually difficult to retain; although well-defined on paper, their clarity is often lost to the realities of time and ongoing maintenance. These restraints--available in steel, aluminum, plastic and PVC--are applied in patios, walkways, driveways, maintenance strips, and jogging trails. As a "tidbit" for seasoned paving restraint installers, Brian K. McThorn of Basalite and distributor of PermaLoc Corporation states, "Many of the times, the edge restraint can be secured after the paver field has been installed, thereby minimizing or reducing the need for cutting of the modular paver field." He adds, "Most aluminum edging is comparable. Cost would be the only issue. In the PVC market, some other PVC products have been known to warp in direct sunlight, be to flimsy, or not allow turf growth directly against the installed paving stones."

President Steve Miller of StableEarth Systems, Inc. and a Licensed KeyStone Retaining Wall Distributor in Southern California, advises industry professionals who are installing retaining walls to "Lay it out...lay it out...lay it out! Lay out the retaining wall first and then build it once-- versus not thinking about the lay out, freeforming it, and then realizing that it is not exactly what you want."

Braun adds, "The base course is the most critical course. Make sure that it is level and straight so the that wall will take on that appearance." Before actual construction, the following conditions need to be assessed: site conditions, overall wall height, soil conditions, surcharges, and the management of excessive water. Evaluate if the ground above or below the proposed wall is level or sloped. Determine how high above grade the wall is going to be. Is the native soil a sandy or gravel type that will allow good water drainage? Or a heavy clay which can hold copious amounts of water and become even more heavy? Direct as much hydrostatic pressure around and away from the wall.

By developing a strong working relationship with local distributors, and by mastering the differences of paving materials and retaining walls, Landscape Contractors can profit in the hardscape market. And, while building another niche for your business...you may just build the next Great Wall of China! lcm