CMU stands for Concrete Masonry Unit, commonly known as cinder block. CMU walls fall into two major varieties, those that are freestanding, and those that are retaining soil (retaining walls.) Both types of walls are secured to a concrete footing (concrete poured into the ground, and reinforced with metal rebar, to which the block will be tied.) Then the block is built up in courses over the footing, and finally, the cells of the block are filled with grout.
Poured In Place Walls
We also install poured in place retaining walls. Poured in place walls are exactly what they sound like: they are walls made out of concrete that is poured into forms in order to create walls, and they are poured in the same place that they will ultimately stand.
Freestanding walls, such as decorative garden walls, or property line walls that don’t retain any soil are constructed with a more shallow footing, and often utilize thinner rebar than those that retain soil. Once the wall is constructed, it can be finished with any number of decorative treatments, such as stucco, stone, or brick.
Retaining walls, unlike freestanding walls, are subject to a great deal of code regulation, and are constructed in a considerably more substantial manner. A soils engineer must analyze the soil around the wall, to determine its weight and density. After the soils report is complete, an engineer must specify the construction details based on the specific site conditions. Retaining walls call for larger footings, and often thicker rebar, and larger block. A retaining wall may be as simple as a property wall that retains two or three feet of soil, or it may be a structural wall on a hillside, retaining 40 feet of soil, and reinforced by structural piles drilled 50 feet into the ground.
Once the block portion of the wall has been constructed, the facing and cap options listed above are available, in addition to many others. The wall may be given a veneer of stacked stone, stone facing, or brick. Another common option is to have the wall finished in smooth or rough colored stucco, which can be made to match the color of the residence quite closely, giving a cohesive look to the entire project.
Walls can be capped with stone, brick, pre-cast concrete, or a poured in place cap. Stone caps, like other flat work, can involve cutting the stone into regular finish shapes, or the stone can be left in its natural shape (with rough, jagged edges.) Brick can also be used as a wall cap. Pre-cast concrete caps are fabricated off-site by pouring concrete into a mold. Pre-cast concrete caps come in a variety of shapes.
Caissons, or drilled piles, and large concrete piles which are craned into deep cylindrical holes, and are used to stabilize walls or foundations when the engineer has determined that additional structural fortification is necessary. After the hole for the caisson is excavated, a steel cage is craned into the ground, into which concrete is poured, created a formidable underground post that is used as an anchor for the entire foundation. Some hillside installations require multiple, large caissons for stability.
Pilasters, (also known as “posts” or “columns”) are similar to CMU walls in terms of their construction. They are constructed from CMU block, and built over a concrete footing which is poured into the ground. They are often incorporated into a wall (approximately every 6-10 feet) to create artistic interest, or they are constructed as freestanding structures. Pilasters, like CMU walls, can be faced with stone or brick veneer, or smooth or rough stucco, and can be capped in the same manner as a CMU wall, with a stone cap, brick cap, or a pre-cast or poured in place concrete cap. Pilasters are often used as anchor points for wrought iron fences. In this case, the pilasters are set every 6-10 feet, and the wrought iron fence is hung between them.