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Brick work needn't be mortar combat

March 07, 2005|by GENE GARY/Copley News Service

Q: I am remodeling and expanding a room off the kitchen that will overlook a landscaped back yard. I want to include an outdoor patio that will be accessed by sliding glass doors from the new room. Brick is my choice for the patio. I have heard that brick can be laid at ground level without mortar or a cement foundation. Is this a project for a do-it-yourselfer who is a fairly adept handyman? I would appreciate any tips you can provide regarding such an installation and the advantages or disadvantages of this type of project.

A: Referred to in the trade as a mortarless, flexible brick system, this type of installation can be very practical. According to the Brick Institute of America, mortarless brick applications are well suited for sidewalks, patios, plazas and driveways where vehicular traffic is light.

Once installed, a flexible brick application still provides quick access to underground utilities, permitting simple reconstruction after any modification or repair work is completed. Without mortar joints, damaged brick pavers are easily replaced. Flexible paving also allows water to filter down to the subgrade, thereby reducing puddles, alleviating flooding and eventually replenishing the water table.

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Cleaning usually requires only a simple hosing. Brick pavers provide a safe, slip-resistant surface for foot traffic.

One advantage of brick paving lies in the flexible nature of its foundation and the action of the pavers themselves. In such flexible brick pavements, the subgrade is compacted and may be covered with a layer of crushed aggregate. A layer of bedding sand is added, and brick pavers are arranged upon the bedding. Sand is spread into the spaces between the pavers as jointing material.

As the whole system compacts with time and use, the bricks interact with the jointing sand and base materials to achieve the quality of "interlock," which holds the pavers in place and distributes the load through the layers down to the subgrade, enabling the surface to contribute to the strength of the whole system. Because a rigid concrete base and mortar are not involved, a flexible brick pavement may be installed with semiskilled or unskilled labor, producing cost savings.

Various combinations of gravel, sand and pavers are used to design a flexible system suited to specific requirements of load, drainage and subgrade stability. In any application, it is critical that the ground and grade be analyzed carefully, that the foundation be planned properly, the correct base materials and pavers specified, and the installation carried out correctly. Although a rigid concrete base in not required, a flexible brick pavement is only a good as the base beneath it.

Optimally, the subgrade is free of tree roots or rocks (they should be removed, and holes filled with appropriate backfill). Proper drainage is essential. In areas with a high water table or soils with high water retention, subsurface drainage systems should be planned.

Depending on the site, drainage can include a layer of washed gravel in the base, installation of a clay drainpipe, or washed gravel providing a perimeter drain. Since these elements affect the strength of the entire system, they should be specified carefully and accurately. Adequate slope should be considered in the design to avoid standing water (a minimum slope of 1/4-inch per foot is recommended, with a maximum grade of 10 percent). The potential for frost heave, which can create permanent changes in the soil and effect the paving surface, should also be addressed.

A rigid edge restraint is required to secure the whole paving system laterally. Since it extends down below the level of the bedding course, the edge also serves to hold that crucial layer in place. Concrete, stone or a row of mortared brick set in concrete may be used, and the border can be planned not only to complement the design of the pavement, but also provide a channel for surface runoff. Border systems of rigid plastic are also available.

The ground must be compacted and stabilized for both strength and drainage. Rammers, vibratory plates or rollers can be used, depending on the compaction needed - 95 percent maximum density is recommended. In areas of high traffic or where drainage is poor, a base layer of 3/4 inch of smaller aggregate should be laid over compacted earth. For the bedding course, which is laid over compacted earth or gravel base, washed sand no larger than 3/16 inch should be used. The jointing sand, which will be spread over the brick pavers and into the spaces between them, should be smaller than that used in the bedding course, and mason's sand graded to ASTM C144 is the standard.

In some instances, a membrane may be useful. When laid between the sand setting bed and the base, this material helps keep sand from sifting down into the base.

The total thickness of the base should be calculated according to specific strength, drainage and heave-resistance requirements, and should be no less than 4 inches.

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