Masonry - Getting to Know Your Structures
Garage floors. To withstand the weight of cars and small trucks, a garage floor slab should be at least 4 inches thick. It should be strengthened with reinforcing wire mesh and be poured on top of at least 4 inches of solidly tamped gravel or sand. A footing running around the perimeter of the slab adds extra support for the garage walls. It can be shallow if there is no significant frost danger in your area or if local building codes permit a “floating” slab—one that can rise or fall an inch or so with frost heave. Otherwise, the footing should extend below the frost line. Anchor bolts in the footing allow you to firmly attach the bottom plate of the wall framing. To handle condensation, blown-in rain or snow, and moisture from vehicles, the slab should slope toward the floor drain or garage door at a rate of 1/4 inch per foot.
Footings. Before building a masonry wall, you must pour a solid footing or the wall will crack. (The exception is a dry stone wall, which has no mortar joints.) How extensive the footing should be depends on how much weight it must carry. For a low garden wall you need only a small pad. A tall masonry or concrete wall, however, requires a substantial footing that extends below the frost line. To support posts for a deck, gazebo, or similar project, you need to set post footings below the frost line in areas with frost or your structure will move up and down with the changing seasons. Simply dig holes and pour in the concrete footings. Or, insert cylindrical concrete tube forms into the holes before pouring the concrete.
Patio surfaces. If you want to lay a patio of bricks, concrete pavers, or tiles that are 3/4 inch or more thick, the most common way is to set them in a bed of sand that rests on a stable surface. If your soil is stable, 2 to 4 inches of sand alone may be enough of a base. But to be sure that your patio does not develop waves and splits, excavate deeper and start with a bed of gravel. Either way, it is important to thoroughly tamp down both the soil and the substrate, using a vibrating tamper, which you can rent. Once the sand is level, install the finish material and fill in the joints between the pavers with fine sand. Other techniques can be used for patio construction. You can set tiles designed for outdoor use in mortar on a solid concrete base or set flagstone directly on firmly tamped soil.
Below-grade walls. To hold back the weight of soil, a wall built below grade must be strong. But even the strongest wall cannot withstand the hydraulic pressure that builds up behind it when soil becomes saturated with rainwater. So, in addition to being built solidly, the wall must have a way for water to escape. Weep holes, small in diameter and spaced 4 to 10 feet apart, allow water to pass through the wall. Or, in the case of a foundation wall, you can direct water along one or both sides of a wall. The most common way to do this is with perforated drainpipe set in a bed of gravel and sloped slightly. A landscaping retaining wall commonly is battered, that is, sloped toward the soil it retains. This gives the wall strength. Structural walls cannot be battered, so build them strong, with plenty of reinforcement.
Selecting Masonry and Concrete Tools
Successful masonry and concrete work requires special techniques. Having the correct tool is essential if you want to end up with straight mortar lines and smooth surfaces. Compared with carpentry tools, masonry tools are not expensive, so don’t hesitate to buy top-quality tools. Cheap tools can make the job more difficult and lead to shoddy-looking work that you’ll have to live with a long time. If your budget is tight, consider renting professional-quality tools rather than buying something from the bargain bin.
A circular saw, framing square, tape measure, chalk line, line level, and 4-foot level are general-purpose tools you’ll need. For mixing and transporting masonry materials and concrete, get a sturdy contractor-quality wheelbarrow with a capacity of at least 3 cubic feet. Make sure the tire is an air-filled type. A mortar box is handy for mixing a lot of material, and a mortar hoe allows you to mix materials more easily than a garden hoe or a shovel.
To prepare the site and move concrete and mortar ingredients you’ll need a round-point shovel for general digging, a square-blade shovel for moving sand and wet concrete, and a spade for squaring up a slab excavation or a footing trench. Use a tamper to prepare soil for masonry surfaces. The beginning steps in finishing concrete require a darby, a wood float, and a bull float. For final finishing, use a magnesium or steel finishing trowel (usually it’s best to have both). An edger is necessary to round off and strengthen edges of slabs. Make control joints with a jointer while the material is still wet. Or, cut joints after concrete is set using a circular saw equipped with a masonry blade.
Cutting bricks, blocks, or stones will be much easier if you have a bricklayer’s hammer, a brick set or masonry chisel, and a 2-pound baby sledgehammer. When building concrete or masonry walls, you’ll need line blocks, line clips, mason’s line, a modular spacing rule, and a plumb bob (a chalk line can be used in place of a plumb bob). For placing mortar, use a well-balanced pointed brick trowel. Use a pointing trowel, 3/8-inch back filler, or a sled jointer to tuckpoint, or force, mortar into joints being repaired. Finish the joints with a joint strike; these are available in different shapes and help you strike (finish) mortar joints between bricks, blocks, or stones. A good stiff hand brush is necessary for finishing the job, along with a variety of stiff brushes for cleanup. If you finish the concrete with a nonskid surface, have handy a stiff-bristled push broom. To cure concrete, you need a garden hose with an adjustable nozzle or an oscillating lawn sprinkler.