Poured Concrete Foundations: Advantages, Limitations and Misconceptions about the Most Popular Base for a Building

Concrete is truly an amazing material. In terms of building foundations, it’s a vast improvement over the materials and methods that came before –like foundations made from stone, brick and cinder block. But there are some misconceptions about concrete that often confuse homeowners when they encounter foundation problems. Let’s try to clear up some of this confusion.

“Cement” isn’t the same as “concrete.”
These terms are often used interchangeably, even among building professionals. But concrete and cement are not the same thing. Cement –or to be more accurate, Portland cement-- is actually an ingredient in concrete. Although additives are sometimes used to alter handling, curing or strength characteristics, the basic ingredients of concrete never change:
    Concrete ingredients by volume:
    7%-15%     Portland cement
    8% or less    Air
    60%-75%    Coarse & fine aggregates (gravel & sand)
    14%-21%    Water

Reinforced concrete can still crack, crumble, shift and settle
Steel reinforcing bars (commonly known as “rebar”) are used to reinforce poured concrete footings and walls. Concrete slabs are reinforced with rebar and with welded wire mesh. Fibers are sometimes mixed into poured concrete to increase its strength as well. These reinforcement techniques are often required by code, and make poured concrete stronger than unreinforced concrete. But even reinforced concrete can crack, shift and settle if soil conditions impose lateral loads on walls and vertical loads on poorly supported slabs. Concrete has exceptional compressive strength but poor tensile strength. In other words, it can’t bend or stretch. If the soil beneath a concrete slab settles, creating a void, the slab can’t flex downward to follow the contour of the recess. Instead, a section of the slab is likely to crack and sink. Likewise, expansive soil that pushes in on a foundation wall can eventually cause the wall to crack, simply because the concrete can’t flex like a wood-framed wall can.  

Concrete absorbs and releases moisture
A bowl, basement or swimming pool made from concrete will hold water, but that doesn’t make the concrete waterproof. In fact, concrete has a sponge-like ability to absorb and release water. As the soil outside a concrete foundation becomes more and more saturated with water, the foundation will also become saturated. Some of this moisture will make its way inside the foundation, either leaking in through cracks or simply making the basement or crawl space damp and humid. Proper waterproofing and (in some cases) dehumidification strategies are necessary to keep basements and crawl spaces dry.

Concrete crack repair isn’t effective if crack causes aren’t addressed
Modern epoxies and patching mortar compounds do an excellent job of filling and sealing cracks. But if the soil conditions that caused the concrete to crack in the first place aren’t corrected, even the best crack repair will eventually fail. That’s why it’s smart to have an experienced foundation repair contractor inspect a damaged foundation before going ahead with repair work. If cracks were caused by expansive soil, soil settlement or soil with poor load-bearing qualities, then these problems will need to be corrected in order to ensure a permanent repair.

Contact Foundation Supportworks by DryZone for a free estimate for foundation repair in Wilmington, DE and other nearby areas.