The crew filling the concrete masonry unit (CMU) block walls with grout. “Solid grouting” CMU walls adds strength and allows the blocks and rebar to function as a single structural unit.
This entire foundation assembly (minus the rebar) is made of cement-based products. Cementitious materials were used by the ancient Assyrians, Egyptians, and Greeks, and modern cement was nearly perfected by the Romans. Cement may be one of humanity’s longest-running and most successful inventions. A Babylonian builder transported to the present might be bewildered by just about everything, but look at this foundation wall and understand exactly what he was seeing.
Though the terms “cement” and “concrete” are often used interchangeably, they have different meanings. If you’re building (or contracting) a foundation, you might want to know the difference between some common cement-based materials.
Most cement used now is Portland cement: a powder of lime, silica, and aluminum that reacts with water to form a powerful, chemically stable bond. Portland cement isn’t usually used by itself, but rather serves as the “glue” for other materials. Concrete is an extremely strong mixture of Portland cement, sand, and crushed rock, typically with as little water as possible. Mortar is a thick mixture of Portland cement, lime, sand, and water usually used to join masonry units. Grout is similar to mortar but has much more water, allowing it to flow into tight or irregular spaces. Grout is often used between floor tiles, or, as here, for filling the voids between CMUs.
Note that water from the grout is leaking through the CMU blocks and mortar. Without additives, cement-based materials are very porous. This is actually an advantage when solid grouting since wetter grout flows into the CMU cavities more easily; then, the excess water from the grout leaks out through the block and brings the grout to a better water content to cure.
Of course, as anyone who has been in a “funky” basement knows, the porosity of cement-based materials can also be a liability because moisture promotes the growth of mold and mildew. I’ll address that in the next post!
Videos taken October 1, 2019. Posted November 14, 2019.
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