Concrete

Concrete is a mixture of sand, coarse aggregate, Portland cement, and water. The sand used in concrete should be blank-run sand, which is fairly round in shape and of various sizes. The coarse aggregate is gravel or crushed stone. Concrete should have aggregate pieces no larger than one-quarter the thickness of the pour. For example, if the pour is less than 4 inches thick, the aggregate should be less than 1 inch in size. Portland cement is made of clay, lime, and other ingredients that have been heated in a kiln and ground into a fine powder. Choose Type 1 cement.

Brick types

Manufactured by firing molded clay or shale, bricks vary widely in color, texture, and dimensions. Despite these variations, they fall into four main categories: common or building, patio, fire, and facing.

Bricks are modular, meaning that they are either one-half or one-third as wide as they are long. The most common nominal modular unit size is 4 inches. Like lumber, bricks are described according to nominal rather than actual sizes. For instance, the actual size of a 4x8 brick is 3 5/8x7-5/8 inches. The nominal size is the actual size plus a normal mortar joint of 3/8 to 1/2 inch on the bottom and at one end.

For outdoor projects that must withstand moisture and freeze-thaw cycles, ask for SW (severe-weathering-grade) bricks. For indoor uses, such as facing a fireplace or a planter, you can use MW (moderate weathering) or NW (no weathering). See Working With Mortar, Related Projects for bricklaying techniques.

Stone types

Building stone is divided into three basic types: rubble, flagstone, and ashlar.

Rubble is composed of round rocks of various sizes. Flagstone consists of flat pieces, 2 to 4 inches thick, of irregular shapes. Ashlar, or dimensioned stone, is cut into pieces of uniform thickness for laying in coursed or noncoursed patterns.

Quarried stone is cut from a mountainside or a pit; fieldstone is rock that has been found lying in fields or along rivers.

Mortar ingredients

Essential to all brick and block construction, mortar is a paste made of water, cement, lime, and sand. Lime slows the setting speed, making the mortar easier to work. Mortar by itself is not as strong as concrete, but it has strong adhesive properties. In combination with stone, brick, or block, it creates extra-strong walls. In addition, mortar serves as an attractive spacer between materials and helps hide their imperfections. It also has a decorative function. Joints can be tooled to various finishes (see Choosing a Mortar Joint, Related Projects). Mortar also can be pigmented.

veneer

Lightweight veneers are made of brick, natural or artificial stone, and terra-cotta (unglazed, fired clay). Except in very dry climates, their use should be restricted to interior projects, such as covering concrete or masonry walls or as a decorative finish over drywall or plaster walls (see Installing Lightweight Brick Veneer and Installing Stone Veneer).

concrete blocks

Concrete blocks and bricks are cast from a stiff concrete mix and are heavy. ("Cinder" blocks, made of light-weight clay or pumice, are not as strong.) Hollow cores in the block help conserve material, make the blocks easier to grip and place, add insulation value, and provide channels for utilities. Use N-grade blocks for places where a wall will be exposed to freezing; S-grade blocks where it will be shielded from the weather.

A typical stretcher concrete block -- the most commonly used block--has a nominal size of 8x8x16 inches and weighs about 45 pounds. Corner blocks have finished edges. A bundle of blocks usually has a mixture of stretchers and corners. Use caps to finish off exposed tops of block walls. Mortarless blocks are laid on top of each other without mortar joints. Once the wall is stacked in place, you reinforce it and grout it.