Chapter 24 Unit pavers.
By reading and practicing the techniques described in this chapter, the reader should be able to successfully complete the following activities:
* Install unit pavers in a recognizable pattern.
* Prepare the site for installation of unit pavers.
* Lay unit pavers.
* Finish a unit paver installation.
RELATED INFORMATION IN OTHER CHAPTERS
Information provided in this chapter is supplemented by instructions provided elsewhere in this text. Before undertaking activities described in this chapter, read the related information in the following chapters:
* Safety in the workplace, Chapter 6
* Basic construction techniques, Chapter 7
* Construction staking, Chapter 8
* Site preparation for paving, Chapter 22
PLANNING THE PROJECT
Construction of unit paver surfaces can be a timeconsuming project. To avoid problems, planning of the installation should precede the work. Following are some considerations for planning a unit paver installation.
Examples of common paving patterns and the pavers that work best in those patterns are identified in Figure 24-1. Certain paving materials may allow only one pattern due to the special shapes in which they are manufactured. Use caution when purchasing brick pavers. If the units are not modular (length twice as long as width), patterns such as herringbone and basket weave will not work. Placement order for each pavement pattern is shown in accompanying figures.
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Paving brick should be solid and without any cores or surface openings.
* Running bond. Running bond is a pattern in which pavers are placed in staggered, horizontal rows. Pavers are placed end to end in one row, and in the next row they are set end to end but are offset by one-half paver. Pavers that work in this pattern include most interlocking concrete pavers, all brick, and any paver that is not modular. Old roadway bricks can often be used only in this pattern (Figure 24-2).
* Stacked bond (also called jack-on-jack). Stacked bond is a pattern in which pavers are placed side by side in even horizontal and vertical rows. Pavers that work in this pattern include many interlocking concrete pavers (all sizes), most brick, adobe, and any paver that is modular (Figure 24-3).
* Herringbone. Herringbone is a pattern that places horizontal and vertical blocks in a diagonal pattern across the paved area. The finished pattern leaves a zigzag, or herringbone, appearance. Halves are required for starting this pattern. Any modular paver can be used in this pattern (Figure 24-4).
* Basket weave. Basket weave places two pavers vertically, and then two pavers horizontally. This alternating pattern is repeated across the entire paved area. Any modular paver can be used in this pattern (Figure 24-5).
* Whirling squares. Whirling squares place four pavers in a square pattern around a half-brick center. This pattern can be offset to create an even more interesting pattern. Halves are required for this pattern. Any modular paver can be used in this pattern (Figure 24-6).
* Modified basket weave. Variations of the basket weave are possible. A common variation includes placing an extra vertical between the vertical and horizontal pairs in every other row. Any modular paver can be used in this pattern (Figure 24-7).
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Interlocking concrete pavers are also available in a variety of shapes that create patterns when installed in stacked or running bond. Some common shapes of interlocking pavers include (Figure 24-8):
* Rectangle. Modular rectangular paver.
* Double score rectangle. Modular rectangular paver with a score line in the center to create an impression of two halves.
* Octagonal. Paver with an octagonal body and interlocking tab.
* Dentated. Paver with an interlocking angled edge.
* Cobble. Combination of modular rectangular and square stones.
* H block, I paver, or dogbone. Paver with an interlocking H shape.
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Base preparation for most unit paving installations is similar to the process described in Chapter 22. However, alternatives do exist to use of an aggregate base with a setting bed for some pavement types. Installation over a previously paved surface or pavement that must carry heavy traffic loads may require an alternative to a crushed stone pavement base. Regardless of material, the base under the entire paved area should be consistent. There is a potential for differential settlement in areas where the unit pavers move from one type of base onto another. Valleys and ridges typically develop over time where base materials change. Some alternative treatments are:
* Concrete or asphalt base. Placement of brick or concrete pavers on a sand setting bed over concrete or asphalt is possible if the base is level and without cracks or serious surface disruptions. If the proposed base surface has broken joints or other disruptions, paving is not recommended. The installation may suffer long-term deterioration if placed on a base that does not drain properly. If pavers are placed on an impervious base that has no drainage, holes should be drilled at the low edges of the subpaving to allow for moisture that has passed through the pavers to drain through the base.
* Placement on mortar base. For some applications, brick or stone paving is placed on a mortar base. See Chapter 26 to review the situations and methods for this type of paving.
EDGE RESTRAINTS FOR PAVED SURFACES
All unit pavers require some sort of edge restraint to prevent the outer courses from wandering. The methods and timing of the placement vary depending on the design of the project, but several choices are described in Chapter 22.
ADHERING PAVERS TO STEPS
Installations that require that pavers be placed on step treads or edges of stoops require setting pavers in a thin bed of mortar or using an adhesive to bond the paver to the material below. Mortared installations should be completed according to the instructions provided in Chapter 21. Pavers bonded to stairs should be cut with joints of 1/16 inch or less. Use a one-part urethane or similar type of adhesive to bond the pavers to the outer edge of the stoops.
PLACEMENT OF SETTING BED
A thin layer of material on which the pavers will be set should be placed over the compacted base. The setting bed should be screeded to a consistent thickness 1 inch to 1 1/2 inches thick across the compacted base. Because the pavers are resting directly on this material, it is also important that the setting bed be sloped in the proper direction and be set at the proper elevation. Clean, coarse, concrete sand is the preferred material for use in a setting bed. Stone dust, fines, limestone screenings, and other materials provide inconsistent compaction after pavers are set. Setting bed sand should contain enough moisture that it forms a ball when squeezed in the palm of the hand. Sand that is too dry will need to be wetted slightly prior to screeding.
Precise screeding of the setting bed can be accomplished using a board notched to fit adjacent pavement or preplaced edge restraint. If using a paved edge for screeding, be certain the base screed is notched to accommodate the thickness of the paver minus 1/4 inch (Figure 24-9). Screeding can also be accomplished by working off 1 inch diameter screed rails that are set directly on the base. Screed only the area of the setting bed that will be paved immediately. Screed perpendicular to the rails when possible. Small sections may need to be screeded in areas where the pavement cross-slopes, or warps, to match existing grades. Screed the setting bed and lift out the temporary screed rails, filling the voids left by the rails with additional sand and smoothing with a steel trowel.
Brick paved surfaces can be separated into smaller paved areas with the use of headers similar to those discussed in Chapter 23 for concrete paving. Typically, decay-resistant wood headers are installed prior to the placement and screeding of the setting bed. The headers are then used as a screed support for leveling the bedding sand.
UNIT PAVER PLACEMENT
Patterns and Edge Course
Before beginning a project, lay a test area large enough to see how the pavers will fit together. For each of the patterns, it is recommended that a soldier course of full pavers be placed around the entire perimeter (Figure 24-10). This course will eliminate placement of cut and partial pavers adjacent to the edge restraint, and will reduce breaking and movement problems.
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To obtain a pattern that is tight and uniform across the paved area, always work from a line that is perpendicular to the edge from which paving begins. Beginning in the wrong place or starting on two sides may lead to a "pinching" or "spreading" of the pattern near the center of the paved area. This error may require additional cutting or relaying of pavement. One method commonly used for paver placement is the T method. The T method begins paver placement in a line perpendicular to one of the project's straight edges. Often, the straight edge used for alignment is a structure or existing paved surface that the paved area abuts. For patios with sight lines through the doors and into the paved surface, consider centering the T layout on the door to ensure a full pattern in front of the door. Near the center of this straight edge, a line is laid out at a 90 degree angle to the straight edge that runs through the center of the paved area. Snapping a chalk line on the screeded bedding sand along this alignment will help maintain the pattern. The pattern is extended along this line for four or five courses, and then the area between the straight and perpendicular lines is filled (Figure 24-11). This method works well for rectangular-shaped areas where minor variations from perfect horizontal and vertical lines will be noticed. Most patterns can be laid with this method.
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Another method for placement is to begin at a structure or wall and work out one row at a time. This method works well for curved walkways and irregular shaped areas where minor variations from perfect vertical and horizontal alignment will not be noticed. This method is also easier for placing herringbone patterns. Without a structure or paved area against which to align paver placement, snap a chalkline across the screeded bedding sand for alignment.
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Placement of pavers using the herringbone pattern may benefit from beginning in the corner of a project rather than using the T or horizontal methods. A corner beginning point allows the establishment of this complex pattern and the continuation of paver placement in one direction across the project. Problems will be encountered with either method if the paved area is between walls that are not at right angles. If this situation is encountered, expect to do a great deal of cutting along one or both walls.
To speed the work, stack several piles of pavers near where the paving placement will begin. Become familiar with the paving units, since interlocking concrete paving block and precast pavers have a top side with a beveled edge. Other pavers may have patterns or textures on the upper side. Pavers placed upside-down will need to be removed and reinstalled with the wearing surface facing up. When paving large areas, several pallets of material may be required. To avoid problems with minor color variations between pallets, select pavers randomly from each of the pallets provided.
Begin laying pavers according to one of the placement methods and patterns previously described. When placing the pavers, set them straight down onto the setting bed. Avoid dropping, angling, or twisting the paver. Allow the weight of the paver to set it onto the sand bed. The paver should be placed with joints of approximately 1/16 inch (Figure 24-12). Some paver varieties have spacers cast into the sides of the paver, which hold the pavers the correct distance apart. Clay brick and other pavers should be set with sides and ends touching.
If a paver pushes too far down into the setting bed, it may leave a small ridge of sand around the bottom edge. This ridge will prevent tight placement of the next pavers. Lift the paver out and lightly smooth the setting bed with a steel trowel. Use caution not to compact or vary the surface level when resmoothing the setting bed.
Paver alignment should be checked often as the laying process moves along. Verify that the joints are straight and that the pattern is correct. Paver alignment can be checked every 10 courses by placing a stringline along joint lines of the pavers. Adjust pavers using a pry bar. Avoid stepping near or adjusting pavers within 1 foot of an unrestrained edge. Continue laying pavers up to the edge restraint that is in place or to the edge marking. Paving operations that are not completed in a single session should be temporarily restrained using a piece of edging. Before continuing paving operations, remove the edging and repair the surface.
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CUTTING AND FINISHING EDGES
Few unit paving jobs can be completed without cutting and placing partial pavers. Planning and selecting simple pavement patterns may reduce the number of cuts that have to be made, but anytime an irregular shape or structure is encountered, cutting can be expected. Pavement should be planned so that full pavers are placed in areas where visibility and traffic is high to improve aesthetics and help avoid breaking and movement. Marking and cutting paving materials is described in Chapter 7. An alternative to cutting half or partial pavers while the pattern is being installed is to place all full pavers first, then mark, cut, and place partial pavers to complete the surface. This will concentrate cutting into a single activity. Use caution not to alter the pattern when placing all full pavers.
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Placing Cut Pavers
Placing cut pavers into position may require tapping the paver with a rubber mallet or shifting of pavers with a masons' trowel. Pavers should fit precisely into the opening (Figure 24-13). If the fit is too snug, trim a bit more off the paver. If the paver can be removed without contacting any adjacent pavers, the cut was too extreme and should be redone using a new paver.
SEATING AND FINISHING THE SURFACE
Following placement of all pavers and edging, the final steps can be applied to a paved surface. This process may vary depending on manufacturers' requirements, but most require that the pavers be "set" into the setting bed and that sand be swept on the surface.
Concrete paving blocks require a mechanical seating of the paving units (Figure 24-14) using a vibratory plate compactor. The seating of pavers vibrates them into the setting bed and forces the setting bed sand up into the joints between pavers. When seating clay brick pavers, use a plate compactor with a rubber mat on the plate to avoid chipping the units. Sweep all debris from the paved surface. Two passes should be made in this initial seating operation. If the plate compactor has multiple settings, use the high-frequency/ low-force setting. Place the plate compactor on the surface, start the equipment, and work the surface from the outside edge into the center. Maintain the plate compactor at least 3 feet away from unrestrained edges. This mechanical seating will push blocks down into the sand leveling course as much as 1/4 inch. When working against existing paving or a preset edging, run the plate compactor on both surfaces at the same time. Placing the plate compactor only on the new pavers may cause them to settle below the existing surface. Examine the surface for any damaged paving units. Pavers may be removed at this stage using a paving puller or two screwdrivers to lift the unit out of the surface. Replace damaged or broken units with new pavers.
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Filling the joints between the pavers helps create interlock and contributes to the waterproofing and stabilization of the surface. This is accomplished by shoveling dry, coarse sand onto the surface of the pavers and sweeping it into the joints. Sweeping diagonally to the joints in two different directions is most effective in working the sand down (Figure 24-15).
Repeating Compacting and Sweeping Operations
Seating with the plate compactor and sweeping of joints should be repeated until joints are full.
SEALING UNIT PAVER SURFACES
Protection of some unit paved surfaces from stains and soiling can be accomplished by sealing the surface. Pavement sealing is a specialized operation that involves washing and application of formulated sealers. Paving manufacturers or distributors should be contacted for recommendations on sealing procedures for unit pavers.
INSTALLATION OF OPEN CELLULAR PAVEMENT
To reduce the problems associated with compaction of turf by pedestrian and vehicular traffic, PVC rings attached to a fiber mesh or precast unit pavers with an open-cell design can be placed directly on a prepared subgrade. (Figure 24-16). Excavate the area where the paving is to be placed. If the paved area is intended to support vehicular traffic, install a compacted granular base as described in the section introduction. Install cellular pavers level and flush with adjacent pavement. Backfill with topsoil to within 1/2 inch of the top of the pavers and apply turf seed over the surface.
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|Title Annotation:||Section 6 Landscape Paving|
|Publication:||Landscape Construction, 2nd ed.|
|Date:||Jan 1, 2005|
|Previous Article:||Chapter 23 Concrete paving.|
|Next Article:||Chapter 25 Dry-laid stone paving.|