• establish an elevated “paved” surface that does not compact the ground or severely disrupt tree roots. Gravel
• to produce a permeable pavement surface. Without an edge, gravel is a formless material that has indistinct edges that merge into surrounding areas. 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). Recycled crushed glass is a specialty material that can be used in the landscape to:
• create areas of bright color that sparkles in the sun light. Both types of gravel are rounded, and so individual stones easily move against one another. The size of individual flags usually fluctuates from 1 foot across or less to 3 feet, although larger slabs are available. Figure 12-23
Example of precast concrete units that replicate the appearance of flagstone. Some potential patterns mimic brick (see Brick, later), whereas others resemble stone in both shape and surface treatment. Gravel Gravel is a small stone that is between 1/4" and 3/4" in size (Figure 12—1). Tile is suitable to:
• complement a Mediterranean style design (Figure 12-35). • where there is need for low maintenance. There are other types of quarried stone as well. 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. 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. Figure 12-31
Common brick patterns for pavement. Wood used for pavement material is milled in standard sizes of 2" X 2", 2" X 4", 2" X 6", 2" X 8", and so on. 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. • extend parallel to or at an angle to the sides of a rectangular area (Figure 12-37). The following paragraphs outline the different categories of pavement materials typically used on a residential site. Ground rubber, or crumb rubber, generally varies in size from 1/8" to 1". Wood Wood is a commonly used unit pavement material that is modular and yet somewhat flexible in its potential uses. Plastic Wood Plastic or synthetic wood is an alternative wood decking material that is available in the same dimensional sizes as true wood. 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). Some of these interlocking units look like they are separate pavement blocks on the surface but are actually one unit. Tile Tile is another unit paver that has a manufacturing process similar to brick. 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. • like fieldstone, establish a visually broken surface with joints filled with gravel, grass, or stepable ground cover or a continuous surface if the stones are tightly spaced and mortared in place. Furthermore, many more designs are possible by combining different shapes and colors within the same pavement surface. Gravel is ideal for the sustainable landscape where the objective is to minimize surface runoff (also see Chapter 3). Figure 12-24
Typical shapes and sizes of concrete pavers. Unit Materials
Unit materials are found or manufactured in fixed sizes and shapes, such as stone, brick, tile, concrete pavers, and wood. 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. Riverstone can be used to discourage a space from being used or serve as a warning edge along another, smoother pavement material (Figure 12-19). Another variable of concrete pavers is the ability for some of them to interlock with each other. Tumbled cut stone can be used to:
• give a paved surface an aged or antique appearance. 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. A potential range of colors including black, gray, buff, golden yellow, red, and off-white augment the appealing texture of gravel. • to define secondary walks or infrequently used spaces. This is a viable, cost-effective alternative to stone. Riverstone Riverstone is a round stone that has been shaped by the force of moving water over thousands of years. Figure 12-33
Brick is best used in areas that require little cutting of individual bricks. Figure 12-20
Examples of precast concrete. Consequently, concrete pavers are one of the most popular and widely used pavement materials on the residential landscape. • provide contrast with visually colder materials such as concrete and flagstone. The result is smoothed angular aggregate that can vary in size from 1/8" to 1/2" across, although most glass used for pavements is in the smaller size range (Figure 12-6). Riverstone is routinely black, gray, tan, wheat yellow, or off-white (Figure 12—17). • provide vibrant color accents with glazed tiles. 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. To slow this process, wood used for a pavement surface is infused with chemicals that preserve its longevity and is generically
Figure 12-35
Tile suggests a Mediterranean character. Other recycled materials that can be used as pavement are shards from shattered clay pots and ground rubber produced from tires. Consequently, precast concrete is a good option for a budget-minded client. 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. Because gravel has no predetermined shape, it can be easily molded to any form on the ground plane (Figure 12-2). • establish a contrast in texture and shape with pavement materials that are more uniform and smooth. Wood is a good pavement material to:
• create a relatively soft surface that has a very slight give underfoot. These stones are sometimes sanded or slightly polished to give them a highly refined appearance. Although concrete pavers are more readily adapted to rectangular paved areas like brick, they can be cut with a masonry saw to fit the edges of almost any ground shape. Two common types of gravel are bank run gravel and pea gravel, so named because of its pea size. Figure 12-30
Examples of unique patterns created with concrete pavers. • define edges and nonwalking surfaces because of its relatively rough quality. Because brick was the construction material in many buildings built in past centuries, brick implies a traditional, old-world quality. 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). Consequently, plastic wood is an environmentally friendly material because it uses recycled materials rather than harvesting existing trees (see Reuse and Recycle, Chapter 3). Consequently, most gravel has a slight give to it underfoot that is often accompanied by a distinct crunching sound. Precisely cut stone can be used to:
• create elegantly smooth pavement surfaces that are often accented by attractive veining of color. Unlike fieldstone, flagstone is typically cut into either irregular, polygonal shapes or rectangular shapes (Figure 12—11). The loose quality of gravel is a potential disadvantage and so it should not be used:
• for pavements where there is a need for snow removal. • 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). However, plastic wood is more expensive to purchase than true wood, and it absorbs and reradiates heat when exposed to the sun. • produce an animated, glittering look that changes with the angle of the sun and direction from which it is viewed. Colors vary
Figure 12-15
Subtle color variations of cut stone. Precast Concrete Precast concrete pavement looks very similar to cut stone except that it is fabricated. Precast concrete is also available in blocks that look like flagstone. The unique aspect of recycled glass in comparison to more traditional pavement materials is its availability in a range of bright, vibrant colors in addition to clear glass. by-products. • be visually compatible with rectangular paved areas. Gravel has a number of uses as a pavement surface in the landscape, including:
• to create an informal and naturalistic character like a garden path or walk through a wooded area. The summary of pavement materials focuses on their appearance and design character, but does not discuss their recommended installation techniques. • fit a variety of pavement shapes. • establish a relatively dark gray surface that has subtle variations in tone and color. Figure 12-21
Example of mixing different colors of precast concrete units. Figure 12-19
Use of riverstone to define a nonwalking surface. • to furnish a textural contrast with smooth or precisely edged pavement materials (Figure 12-3). A particular mixture of gravel may consist of one color or be an assortment of many colors, giving it a more mottled appearance. In addition, some manufacturers add recycled sawdust or other minuscule wood
Figure 12-37
Wood is best used when it is parallel or at an angle to the sides of an area. Many concrete paving units are simple, flat-sided forms like brick that fit together by adjoining the straight edge of one with another. Fieldstone’s irregularity makes it a potentially difficult surface to walk across, especially for anyone with walking impairments. Clay pot fragments furnish a walking surface that has a deep red color and a distinct texture (Figure 12—7). 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). Figure 12-9
Fieldstone is best used as pavement in secondary use areas. These types of stone have numerous shapes, colors, and uses as outlined in the following paragraphs. Gravel is potentially difficult to walk on or to push wheeled equipment across and so should not be used for frequently used spaces or paths. • to establish an attractive, pliable texture on the ground plane. The principal recommendation for designing with gravel is that metal or plastic edging, wood, or another pavement material should contain it (Figures 12-4 and 12-5). Figure 12-17
Assorted examples of riverstone. 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. Precast concrete pavers cost less that similarly sized and shaped cut stone because they are mass-produced. Other shapes, such as octagons, and colors are also available. Additionally, fieldstone may not provide an even, level surface for outdoor furniture. Some fieldstones are further noted for fossil imprints, embedded aggregates, and/or erratic veining of color (Figure 12-8). • produce a permeable pavement surface if the joints are filled with ASTM #8 or #9 gravel or lawn. The exact appearance of quarried stone varies widely depending on the geological source of the stone and how it is processed. Like gravel, the color may be uniform or a mixture of a range of colors. • create either rectangular or circular patterns. • create elaborate patterns of mixed shapes and/or colors. Figure 12-2
Gravel readily defines curved and irregular paved areas. The term is derived from the fact that it is a plastic material, often generated from recycled milk, water, and juice containers. Fieldstone
‘Fieldstone
Figure 12-10
Use of fieldstone to create broken joints for stepable groundcovers. However, tile is much thinner than brick and is often unable to withstand freeze-thaw cycles, thus restricting its use to warmer climates. Each manufacturer has its own color palette, so it is best to contact them to determine the exact colors available. Figure 12-11
Typical flagstone shapes. The color is usually black, although it can be purchased in dark browns, a range of brick reds, or other colors depending on the manufacturer. ° catting. • produce a permeable pavement surface with certain available pavers or when the individual paver units are separated by ASTM #8 or #9 gravel. Another form of cut stone is tumbled stone. • express a refined and formal design style. slow the rate of movement across an area. The material is put down on the ground to a desired depth and held in place by a containing edge. The 2" X 4" and 2" X 6" dimensions are the ones most commonly used for pavement, although these can be cut and/or combined to create variations in patterns (Figure 12-36). The size of most individual precast concrete paver units is between 1 and 2 feet across. The most common categories
Figure 12-7
Example of shattered clay pots used as a pavement surface. Figure 12-4
Gravel needs to be contained on its edges. of stone include fieldstone, quarried stone, and riverstone. Many are stones cut into precise square and rectangular shapes from limestone, travertine, and quartzite. • establish a visually broken surface with joints filled with gravel, grass, stepable ground cover, and so on (Figure 12—10). This conventional size can be assembled into a number of patterns, some directional and some static (Figures 12-31 and 12-32). Gravel is easily kicked or tracked out of its location and carried to adjoining areas of the landscape, thus requiring extra upkeep. Figure 12-12
Typical flagstone colors. • establish a wood-like surface that is in direct contact with the ground. Because of its thin dimension, tile must usually be placed as veneer on top of a concrete base. Figure 12-36
Possible patterns created by standard lumber sizes. Glass from bottles and other products is crushed and then tumbled to slightly round off jagged edges and points. • establish a decorative contrast to more earthy ground plane materials. Figure 12-1
Typical gravel size. • 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). Concrete pavers make it possible to create distinct patterns that are not achievable with other materials (Figure 12-30). 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. • to serve as a ground cover in arid climatic zones or other locations where it is difficult for plants to grow. • create an elegant, smooth pavement surface. • produce a permeable pavement surface like gravel. Curvilinear — form requires bride can-ft+ reofanqotor
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pavement. Brick Brick, or clay paver, is a unit pavement material manufactured by pouring liquid clay into a mold and then firing it at extremely high temperatures to harden it into its permanent form. Although the exact form varies with manufacturer, some have holes cut in a corner,
Figure 12-26
Examples of interlocking concrete pavers. • produce either directional or static patterns depending on the shape and organization of the stone (Figure 12-14). Loose Materials
Loose materials, also called “aggregates,” are small individual stones or chips that are amassed as a pavement surface without being physically held together by an adhesive. Most precast concrete is square or rectangular in shape with a smooth, concrete-gray surface (Figure 12—20). 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. 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. One specialized type of interlocking concrete paver is permeable pavement. • mimic traditional brick or stone patterns, but for less cost. Flagstone is suitably used to:
• create a smooth surface that simultaneously suggests refined permanence and an association with nature. Figure 12-38
Wood can create a pronounced directional pattern. Tile is available in a diverse range of sizes from several inches across to approximately 18 inches across.
