A poured concrete foundation is the most common type of residential foundation found in the United States today. Except for areas too far from ready-mix concrete plants, the poured foundation has largely replaced various forms of masonry including concrete block, brick and stone.
Both poured concrete and masonry foundations have approximately the same load-bearing capabilities but the monolithic walls of a poured foundation are stronger against lateral pressures than masonry and have no mortar joints to admit seepage.
Like a masonry foundation, a poured concrete foundation sits on a footing, which is a poured concrete pad wider than the wall that supports the foundation and helps distribute its weight and that of the aboveground structure. The footing’s width is determined by the size and construction of the house and the load-bearing characteristics of the underlying soil.
The footing can be constructed at various depths for a crawl space or full basement but must always be below the frost line to avoid heaving and other movement.
The foundation walls are poured into wood or metal forms that are assembled on top of the footing. When the concrete has cured, the forms are removed and the concrete basement floor is poured over a vapor barrier. After the first floor joists have been installed the foundation is now braced top and bottom and the surrounding excavation can be backfilled and compacted.
The whole thing sounds pretty watertight but there are several ways in which even the strongest-built poured concrete foundation can admit seepage and a number of ways it can be prevented or stopped.
Most often, basement waterproofing is done to an existing home, often years or even decades after it was built but most effective waterproofing techniques can also be done during construction. It can make sense to do this, especially with installations that require excavation because they can be done before the foundation is backfilled or the basement floor poured.
For example, a poured concrete foundation can admit water through patches of porous concrete or over the top of the foundation wall. This can be prevented, or stopped, by applying an exterior waterproofing membrane to the foundation wall. The membrane consists of asphalt-modified polyurethane and is applied thickly to the wall surface with a trowel to form a permanent water barrier. Drainage board and insulating material can also be added.
When done during construction, the membrane replaces “damp-proofing,” a thin spray coating designed to prevent condensation on interior walls. After construction, installing the membrane requires excavation along all affected walls.
In areas where the water table is high, exterior drain tile is often added to carry off the ground water to a sump pump.
Another way water can enter a basement is through the joint between the foundation wall and the footing that is known as the cove joint. Cove seepage occurs when hydrostatic pressure under the foundation forces water in through this small opening. Installing interior drain tile, perforated pipe buried in washed gravel level with the footings, will alleviate this pressure and bear water off to a sump pump.
The most common source of seepage in a poured concrete foundation isn’t found during construction and can be repaired only after the fact. Non-structural cracks are caused by settling or lateral pressure on foundation walls and can occur at random locations. The best way to stop water seepage from these cracks is to inject them with expanding polyurethane, which seals the crack all the way to the outside soil and remains flexible after curing to prevent further cracking caused by minor foundation movement.
No matter whether the home is still being built or is 100 years old, the homeowner who wants to prevent or stop basement seepage will need the advice and services of a full-service basement waterproofing contractor who is experienced with working on new homes and old. At U.S. Waterproofing we have collaborated with homeowners and members of other building trades to find the exact right solution for their basements and we’ve succeeded time and time again as more than 300,000 satisfied customers will tell you. Why not ask for our free advice?
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