Masonry Magazine April 1995 Page. 23
Setting Beds
Setting beds are the materials on which brick pavers are placed. Common setting bed materials are mortar, asphalt and building felt.
Mortar. Two important characteristics of mortar are air content and water/cement ratio. An air content for paving mortars between approximately 10 percent and 15 percent is optimal. Increasing air content too much will reduce bond between the brick paver and mortar. To address the water/cement ratio, the mortar should be mixed with just enough water to make it workable. The thickness of the mortar setting bed should be between ⅜ in. and 1 in. (10 mm to 25 mm).
Asphalt. Asphalt setting beds typically consist of approximately 7 percent asphalt and 93 percent sand. The asphalt setting bed is used over a concrete or asphalt base. The thickness of the asphalt should be approximately ¾ in. (20 mm).
Building Felt. Brick may be placed directly on a new or existing asphalt or concrete base. In these applications, building felt may serve as a cushion between the pavers and the base, which can accommodate small dimensional variations of the base and pavers. Two layers of No. 15 building felt or one layer of No. 30 building felt is appropriate.
Base Materials
Base materials consist of crushed aggregate, gravel, sand, asphalt and concrete. Asphalt and concrete bases often require an aggregate subbase. Steps and ramps usually are built on concrete bases, whereas patios and terraces may be supported on any of the base materials listed.
Aggregate Bases. Aggregate bases include crushed stone, gravel and sand. Heavier loading or areas subjected to frost heave may require crushed stone. Open-graded aggregate (gravel) is often used in areas of poor drainage, areas subjected to frost heave or when porous pavements are designed. The proper aggregate size depends on the depth of the layer and the size of the compaction equipment. Maximum aggregate size is usually ¾ in. (20 mm) diameter.
In residential pedestrian applications, sand bases can be used when the subgrade compaction is ensured, when bearing on undisturbed earth and in areas where frost heave is not a consideration. Sand used as a base material should be a concrete sand conforming to ASTM C 33 and be clean and free of deleterious materials.
Concrete Bases. New or existing concrete bases may be used to support brick paving. New concrete should be installed following recommended concrete practices. Where mortar is used to bond brick pavers to the concrete, the concrete should have a rough textured finish. Caution should be used if brick is placed over an existing concrete slab. The existing concrete slab must be sound and any major cracks filled adequately with concrete or mortar.
Asphalt Bases. New or existing asphalt bases may used to support mortarless brick paving. Proper asphalt materials are generally determined by paving contractors or the asphalt plant and are beyond the scope of this Technical Notes. Asphalt bases should not be used to support mortared brick paving.
CONSTRUCTION
One of the most important factors in long-term pavement performance is proper installation. Critical elements include proper base compaction, proper edge restraints and full mortar joints, if used. There are numerous ways to install brick paving, and techniques tend to vary by region. The recommendations in this Technical Notes are based on experience and provide a minimum level of workmanship necessary for satisfactory performance. More information on construction of brick pavements may be found in Technical Notes 14 Series.
Base Preparation
Proper compaction of the subgrade (soil) and base is one of the most critical factors in pavement installation. Pavements rely on the strength of the base to adequately resist loads. Poorly compacted aggregate bases usually lead to undulations (rutting) or cracking of the pavement. Most patios, steps and ramps are built adjacent to a building or residence. These are often areas over backfill rather than undisturbed earth, making proper compaction even more critical. Compaction of the subgrade should be done with the largest equipment possible so that proper compaction is achieved. Once the subgrade is compacted, the base may be built on top. The base material should be spread and compacted in layers or lifts. The thickness of each layer must be consistent with the size of compaction equipment, but never exceed 4 in. (100 mm). Vibratory rollers may be necessary, although for most residential applications plate compactors provide enough force. Typical compaction criteria is 95 percent maximum density.
Mortar Installation
When brick are installed with mortar, standard bricklaying or tile setting procedures should be followed. The preferred method of mortar placement is with a trowel. The concrete base should be clean and slightly dampened, but surface dry prior to placing the mortar. Brick pavers should be buttered on the ends and shoved into the mortar setting bed. All joints intended to receive mortar should be solidly filled. The joints should be tooled with a metal jointer. A shallow concave joint profile is preferred for proper compaction of the joint and to keep water from ponding on the mortar joints.
CONCLUSION
This Technical Notes describes elements considered in landscape design including master planning and environmental aspects of landscape architecture. Design of pavements, steps and ramps is discussed. Materials and construction of these elements and the most critical requirements for each are outlined.
The information and suggestions contained in this Technical Notes are based on the available data and the experience of the engineering staff of the Brick Institute.