Although there may be a few exceptions found in older homes, houses in the Chicago area will generally rest on one of two types of foundations: concrete or masonry.
All modern foundations, whether concrete or masonry, start with footings or “footers,” which are concrete pads that describe the perimeter of where the foundation will sit. Footings are generally 12 inches deep and range from 12 inches to more than 3 feet in width, depending on the size of the house, type of construction and load-bearing characteristics of the soil underneath. The footings spread the weight of the foundation and help keep it stable and plumb.
Poured concrete foundations are most common in Chicago and its suburbs. These foundations are built by erecting a network of concrete forms on top of the footings, centered in the middle of the pad. Concrete mix is poured into the forms while workers spread it and ensure that it is purged of air. Hardware is set into the top of the foundation before the concrete cures to anchor the aboveground construction to follow.
Modern masonry foundations typically consist of concrete blocks, often called “cinder blocks,” that are laid course by course in a running pattern on top of the footings. These block foundations are common in Milwaukee and northwest Indiana. Masons use a mortar mix to adhere blocks to one another and build in openings for windows and doors. Older homes may have masonry foundations built of stone, brick or a webbed terra cotta block called “telephone tile.”
Repairing Concrete vs. Masonry Foundations
The differences in construction methods dictate different approaches to repairing concrete or masonry foundation walls that have suffered structural damage due to settling or lateral pressure. Any foundation that has dropped or sunk must be raised and leveled by underpinning, preferably with hydraulic push piers.
Concrete Foundations — When a wall of a poured concrete foundation suffers damage it begins to crack, often at similar points in each corner and across the middle. As the pressure continues, the monolithic wall begins to tip inward from the top, a process called “rotation.” Repairing this wall requires stabilization so that it doesn’t move any farther and can be done by several methods. An older method called wall anchors placed a large steel plate in a hole outside the foundation, then extended a long threaded steel rod through the wall, with another plate on the inside and bolted it through the exterior plate. Regular tightening by the homeowner would keep the wall from further movement if everything stayed in place.
Another method used large steel I-beams upright against the wall to prevent further movement.
Today, two less obtrusive methods are used. For concrete walls that have moved less than two inches, repairs are done with carbon fiber strips epoxied to the wall in locations determined by engineering data. For walls with more movement, low profile channel steel beams are used to stabilize the wall; these beams are small enough to be covered by a 2” x4” stud wall.
Masonry Foundations – Because masonry walls are not monolithic, the damage caused by lateral pressure is seen mainly in the mortar joints between blocks or other masonry units. Walls tend to crack in stairstep patterns in horizontal and vertical mortar joints and, as pressure increases, to bow or bulge in the center. Left unrepaired, the blocks will begin to move out of line as they separate completely from the mortar.
The old method of repair for severely damaged masonry walls was to shore up the house, rip out the wall and rebuild it. This was not only expensive and time-consuming but did nothing to prevent future damage. The steel I-beam method was also used on moderately damaged walls.
The modern method of carbon fiber repair is well suited to block walls and others with regular shaped masonry units such as brick and is done similarly to the process used on concrete walls. Stone foundation walls, because of their irregular surface, will require low-profile steel to stabilize them as will other masonry that has experienced extreme movement.
Whatever the construction and no matter the method of repair, foundation damage repair is serious business and requires the services of an expert. The foundation repair experts at U.S. Waterproofing are experienced in the latest permanent repair methods and make use of engineering data to ensure that work is done in the least inconvenient and most cost-effective manner for the homeowner. Why not ask us for a free consultation if your foundation is showing signs of damage?