Unit Materials

Unit materials are found or manufactured in fixed sizes and shapes, such as stone, brick, tile, concrete pavers, and wood. Generally, unit materials are more expensive to use than either loose materials or adhesive materials because they require more labor to quarry, manufacture, and install.

Stone Stone is a unit material that embraces a broad range of types and shapes depend­ing on where it is found and how it is processed for use. The most common categories

of stone include fieldstone, quarried stone, and riverstone. These types of stone have numerous shapes, colors, and uses as outlined in the following paragraphs.

Fieldstone Fieldstone is any irregularly sized and shaped stone randomly found at or near the earth’s surface without quarrying. Fieldstone may be angular or somewhat rounded depending on its geological source. Fieldstone is typically used in the form in which it is unearthed and can be employed in the landscape to:

• create a naturalistic, rugged surface characterized by random sizes, nonuni­form shapes, bumpy surface texture, and deformities. Some fieldstones are further noted for fossil imprints, embedded aggregates, and/or erratic veining of color (Figure 12-8).

• define secondary paths or infrequently used spaces (Figure 12-9). Fieldstone’s irregularity makes it a potentially difficult surface to walk across, especially for anyone with walking impairments. Additionally, fieldstone may not provide an even, level surface for outdoor furniture.

• establish a visually broken surface with joints filled with gravel, grass, stepable ground cover, and so on (Figure 12—10). Because of the irregular nature of fieldstone and the challenge of putting oddly shaped pieces together, it is eas­ier to establish a fragmented pavement surface than a continuous one.

• establish a contrast in texture and shape with pavement materials that are more uniform and smooth.

Quarried Stone As the name implies, quarried stone is any stone that is obtained through a mining-like process that removes the stone from the earth and cuts it into a desired size and shape. The exact appearance of quarried stone varies widely depend­ing on the geological source of the stone and how it is processed.

Flagstone is one of the most common types of quarried stone and is character­ized by being split into relatively thin slabs or “flags” that are customarily 1" to 1—1/2" thick. Unlike fieldstone, flagstone is typically cut into either irregular, polygonal shapes or rectangular shapes (Figure 12—11). The size of individual flags usually fluc­tuates from 1 foot across or less to 3 feet, although larger slabs are available. The typ­ical color of flagstone varies from gray to a limestone yellow, including many subtle variations of gray that are shaded with blue (often called bluestone), buff, light red, or brown (Figure 12—12). Flagstone is much more expensive than fieldstone.

Flagstone is suitably used to:

• create a smooth surface that simultaneously suggests refined permanence and an association with nature.

• establish a relatively dark gray surface that has subtle variations in tone and color.

widely but typically include yellows, warm buffs, rose reds, and so on (Figure 12—15). These stones are sometimes sanded or slightly polished to give them a highly refined appearance. Cut stone is relatively expensive and so is commonly reserved for clients who have more expansive budgets. Precisely cut stone can be used to:

• create elegantly smooth pavement surfaces that are often accented by attrac­tive veining of color.

• express a refined and formal design style.

• be visually compatible with rectangular paved areas.

Another form of cut stone is tumbled stone. This stone is rectangular in shape, usually thicker than flagstone, and characterized by slightly rough or irregular edges (Figure 12—16). Some tumbled stone resembles concrete pavers, although it costs more per square foot. Tumbled cut stone can be used to:

• give a paved surface an aged or antique appearance.

• define edges and nonwalking surfaces because of its relatively rough quality.

• create either rectangular or circular patterns.

Riverstone Riverstone is a round stone that has been shaped by the force of moving water over thousands of years. It is obtained from riverbeds and lakeshores, thus sometimes being referred to as “river wash.” The normal size of riverstone used as a pavement material is from 1" to 2" even though larger dimensions are available for other landscape applications. Riverstone is routinely black, gray, tan, wheat yellow, or off-white (Figure 12—17). Most riverstone possesses a uniform surface color; some possesses a mottled appearance with specks and streaks of different colors.

Riverstone is appropriately used as a pavement material to:

• provide a distinct bumpy texture of numerous rounded stones partially pro­truding up from the pavement surface (Figure 12—18).

Precast Concrete Precast concrete pavement looks very similar to cut stone except that it is fabricated. The term precast means that the concrete is poured into a reusable mold in a manufacturing plant, cured, and sold as a unit pavement material. Most precast concrete is square or rectangular in shape with a smooth, concrete-gray surface (Figure 12—20). Other shapes, such as octagons, and colors are also available. The size of most individual precast concrete paver units is between 1 and 2 feet across. Precast concrete pavers cost less that similarly sized and shaped cut stone because they are mass-produced.

Square and rectangle precast concrete pavers are suitable to:

• create the appearance of cut stone, but for much less cost. Consequently, pre­cast concrete is a good option for a budget-minded client.

• produce unique patterns based on different colors of concrete units (Fig­ure 12-21).

• establish a continuous surface if the paver units are tightly spaced and mortared in place or a visually separated surface with joints filled with gravel, grass, or stepable ground cover (Figure 12—22).

• produce a permeable pavement surface if the joints are filled with ASTM #8 or #9 gravel or lawn.

Precast concrete is also available in blocks that look like flagstone. The paving block is again manufactured in a mold that produces a unit resembling a group of in­dividual stones mortared together side by side (Figure 12—23). The shape of this unit is such that it can be added to other units in a modular form to cover an entire paved surface. A quick glance suggests that the pavement is composed of different “stones,” though a closer inspection reveals the repetitive nature of the pavement. This is a vi­able, cost-effective alternative to stone. This type of precast concrete paver has similar uses as fieldstone except that it establishes a more uniform surface with tight joints be­tween the modular units.

Concrete Pavers Concrete pavers are another form of precast paving units with an extensive range of potential shapes and colors. Consequently, concrete pavers are one of the most popular and widely used pavement materials on the residential landscape. The most common form of concrete paver is the brick shape that measures about 2" x 4" X 8". In addition, concrete pavers are obtainable in rectangles, squares, oc­tagons, and a host of other shapes that fit together in a modular fashion (Figure 12—24). Some concrete pavers have a cleanly defined form; others possess a tumbled appear­ance with rough edges. Potential colors range from brick-like reds to various shades of gray, buff, tan, and brown (Figure 12—25). Each manufacturer has its own color palette, so it is best to contact them to determine the exact colors available.

Another variable of concrete pavers is the ability for some of them to interlock with each other. Many concrete paving units are simple, flat-sided forms like brick that fit to­gether by adjoining the straight edge of one with another. However, other concrete pavers are fabricated with a more elaborate profile so that they interlock with adjacent paver units of the same shape (Figure 12—26). Some of these interlocking units look like they are separate pavement blocks on the surface but are actually one unit. Interlocking con­crete pavers have the advantage of forming a structurally strong pavement surface that supports more weight in comparison to a pavement composed of many flat-sided units.

One specialized type of interlocking concrete paver is permeable pavement. Although the exact form varies with manufacturer, some have holes cut in a corner,

whereas others possess small protrusions along their sides (Figure 12—27). When as­sembled together, these pavers create spaces between individual units that should be filled with ASTM #8 or #9 gravel to allow water to percolate to the ground below (Figure 12-28).

A distinguishing quality of all concrete pavers is the diverse range of possible patterns that are available as standard designs for any given product line (Figure 12-29). Some potential patterns mimic brick (see Brick, later), whereas others resemble stone in both shape and surface treatment. Furthermore, many more designs are possible by combining different shapes and colors within the same pavement surface. Some patterns can even create a letter, symbol, or logo by selecting appropriate colors and carefully cutting the individual paver units to the required size and shape.

Concrete pavers are appropriately used to:

• provide a utilitarian surface that can be used in almost any pavement, includ­ing walks, entrance ways, terraces, work areas, driveways, and so on.

• mimic traditional brick or stone patterns, but for less cost.

• create striking patterns composed of different shapes and colors within the pavement surface. Concrete pavers make it possible to create distinct patterns that are not achievable with other materials (Figure 12—30).

The dark orange-red color of brick is the most universal, although darker and lighter variations along with shades of gray and brown are also obtainable.

Brick can be employed as landscape pavement to:

• establish an appealing color and texture in places where a warm, friendly at­mosphere is desired.

• suggest a historical character. Because brick was the construction material in many buildings built in past centuries, brick implies a traditional, old-world quality.

• visually unify a pavement surface with a brick house.

• provide contrast with visually colder materials such as concrete and flagstone.

For proper design and installation, brick should:

• be contained by a metal or plastic edge, stone or brick mortared into place, pressure-treated wood, or another pavement surface.

• be placed in rectangular or circular pavement areas to minimize installation costs associated with cutting and fitting individual brick to an irregular or curved edge (Figures 12—33 and 12—34). Although brick can be cut and fit­ted to any ground shape, it costs more to do so.

Tile Tile is another unit paver that has a manufacturing process similar to brick. However, tile is much thinner than brick and is often unable to withstand freeze-thaw cycles, thus restricting its use to warmer climates. Tile is available in a diverse range of sizes from several inches across to approximately 18 inches across. The color of tile varies from earth tones to glazed colors. Because of its thin dimension, tile must usu­ally be placed as veneer on top of a concrete base.

Tile is suitable to:

• complement a Mediterranean style design (Figure 12—35).

• create an elegant, smooth pavement surface.

referred to as pressure-treated wood. Some wood such as cedar and redwood naturally possesses chemicals that slow its decomposition and so is a good, though more expen­sive, alternative as a pavement material. To further its longevity in the landscape, wood should be used in places such as decks where it will not be in direct contact with ground. Wood can sometimes be placed directly on the base plane when the ground below is gravel or well-drained soil with a substantial sand content.

Wood is a good pavement material to:

• create a relatively soft surface that has a very slight give underfoot.

• extend parallel to or at an angle to the sides of a rectangular area (Figure 12—37). Wood is less adaptable to curved areas, although it can be cut to define broad curves if the individual wood planks are cut at their ends.

• create a distinct directional pattern resulting from the linear quality of wood (Figure 12-38).

• produce a permeable pavement surface by allowing surface water to drip be­tween individual boards to the ground below.

• establish an elevated “paved” surface that does not compact the ground or severely disrupt tree roots.

Plastic Wood Plastic or synthetic wood is an alternative wood decking material that is available in the same dimensional sizes as true wood. The term is derived from the fact that it is a plastic material, often generated from recycled milk, water, and juice contain­ers. In addition, some manufacturers add recycled sawdust or other minuscule wood
by-products. Consequently, plastic wood is an environmentally friendly material because it uses recycled materials rather than harvesting existing trees (see Reuse and Recycle, Chapter 3). Plastic wood is available in a number of colors, many of which simulate var­ious colors of stain. The advantage of plastic wood is that it does not require periodic sur­face treatment to preserve its water resistance. However, plastic wood is more expensive to purchase than true wood, and it absorbs and reradiates heat when exposed to the sun.

Plastic wood is a good pavement surface to:

• fulfill the same uses as real wood but without the long-term maintenance re­quirements.

• use as a sustainable alternative to real wood.

• establish a wood-like surface that is in direct contact with the ground.

Figure 12-38

Wood can create a pronounced directional pattern.