WATER SEEPAGE - CAUSES AND CONTROL

Depending on the topography, drainage conditions of the soil, and groundwater level (water table), the basement or crawl space might be vulnerable to water seepage. Water seepage, as used herein, is a general term that refers to water intrusion into the lower level of the structure. It might manifest itself as a small wet area, a puddle, or layer of water completely covering the floor. If the ground under and around the house is wet, water can seep into the basement through cracks and open joints in the foundation walls or floor slab. Since water seepage can be caused by a number of factors and water can leak into the basement at any number of locations, it is important to determine the cause and source of the seepage so that the proper corrective action can be taken.

For example, if water is entering the basement through the foundation walls, installing a sump pit and pump below the floor slab will not correct the problem. Similarly, if water is seeping into the basement through the floor slab, sealing the walls will not correct the water-infiltration problem. All too often the unsuspecting homeowner is talked into a full waterproofing job, which can cost several thousand dollars, when all that might be needed is to redirect the water discharging from the roof drainage system (gutters and downspouts) so that the water does not accumulate around the foundation.

High groundwater level

Water entering the basement through the floor slab is an indication that water pressure is being exerted on the underside of the floor. When the level of the water below the house is sufficiently high (due to a seasonal high water table or improper drainage) so that it pushes on the underside of the floor slab, it seeps into the basement through cracks, open joints, or porous sections of the slab. If the pressure is great enough, it can cause the floor to crack and heave.

If the seepage is minor, it can often be controlled by sealing cracks and open joints with a hydraulic cement and coating any porous areas of the slab with a cement-base or epoxy sealant. However, a better solution would be to lower the level of the water below the floor slab. This can be done by installing a sump pump below the slab. Subsurface water then flows into the sump pit in the manner of water flowing into a hole dug at the seashore. The water is then removed by the pump and discharged, either into a storm drain or at a point sufficiently far from the house, so that it will not be absorbed by the ground and flow back under the basement floor slab.

Depending on how the floor slab was constructed, a single sump pump might or might not be adequate to lower the level of the sub-surface water. In areas with a seasonal high water table, a concrete floor slab should be installed over a gravel base. Water that accumulates below the slab can then flow through the voids between the gravel and drain away or flow into a sump pit. However, in many houses the floor slab has been installed directly over soil with poor drainage characteristics or over an inadequate gravel bed. In this case, water in the saturated area below the slab will not readily flow into a sump pit, and to control the water buildup, it is necessary to install a series of perforated drain pipes below the floor slab that terminate in the sump pit. Caution should be observed when lowering the level of the groundwater below the basement floor. With some slow-draining soils, such as silts and clays, some soil can wash out from around the foundation footing. This can result in unequal settlement, which could crack the walls. Whether a sump pump or drain pipes are needed below the floor slab is an evaluation that should be determined by a professional.

If the house is located in an area with a high incidence of power failures, you should not depend solely on an electrically driven sump pump to control groundwater seepage. It is possible for the power to be knocked out when the water level below the floor slab is rising. As a precautionary measure, there should be an auxiliary water-actuated (non electrical) ejector pump in the sump pit. The pump is connected to the house water supply and is activated by a float control. This type of auxiliary control is particularly helpful in vacation homes where the house will be vacant for extended periods. However, it will be of no help if the water to the house is supplied by an electrically driven well pump.

If you install a water-actuated sump pump, it's important that you include a back-up flow preventer on the water supply because of the potential for contamination as a result of the cross connection.

Hydrostatic pressure, walls

Water seeping or leaking through the foundation walls into the basement is due to a hydrostatic pressure being exerted on the walls by saturated soil. This condition is the result of water accumulation around the foundation. The best way to control this type of problem is to minimize the amount of water that accumulates around the foundation. The following are some of the more common causes of water accumulation around the foundation, which can easily be detected and corrected by the homeowner.

• Missing or defective gutters and downspouts to handle the rain runoff from the roof. The downspouts must discharge the water away from the structure. All too often, an elbow or splash plate at the base of a downspout is missing, so that the water is discharged directly around the foundation.
• Improper grading. The ground immediately adjacent to the structure should be pitched so that it slopes away from the building. Around many homes this area is incorrectly pitched, resulting in surface water (rain or melting snow) collecting around the foundation.
• Unprotected basement-window wells. The area around basement windows, if not shielded from rain or serviced with a drain, can easily accumulate water that can leak through window joints or seep down around the foundation.
• Uneven settlement of walkways or patio. Occasionally the walkways around the house or the patio have settled and are sloping toward the house. As with improper grading, this condition can cause surface water to collect around the foundation.
• Leaky garden spigots. Most homes have exterior-mounted spigots for connection to a garden hose. If the valve is faulty or is not tightened properly, water will drip or leak around the foundation. Water dripping at a rate that fills one cup per minute results in 90 gallons of water per day accumulating around the foundation. This water enters the basement through cracks or open joints in the foundation wall.

When the house is located on an inclined lot, surface and subsurface water flows toward the house from the higher portions of the lot. In this case, depending on the incline and the amount of water involved, water-flow control measures will include grading the lot on the high side, so that there is a swell to collect and redirect surface water around the house, and installing a French drain (curtain drain) below the ground to intercept subsurface water and direct it away from the house.

If the amount of water that accumulates around the foundation walls is not excessive, it can be prevented from penetrating into the interior by sealing cracks and open joints on the inside walls with a hydraulic cement and then coating the walls with a cement-base or epoxy sealant. Coating the wall is particularly helpful when the wall is porous, like a cinderblock wall. However, when an excessive amount of water accumulates around the foundation wall, as with a poorly drained soil such as clay, waterproofing the exterior surface of the basement walls might be more effective than treating the interior surface. In addition, a perforated drainpipe is normally installed near and parallel with the foundation footing. The purpose of this footing drain is to carry away water that is accumulating around the foundation and thereby reduce the hydrostatic pressure.

For the footing drain to operate properly, it must have a free-flowing outlet. I know of several cases where builders installed faulty footing drains around houses during construction. The problem was that the drains completely encircled the houses like a doughnut and had no free-flowing outlets. These footing drains were of absolutely no value. Even though initially a footing drain might function properly, over the years it can malfunction because the perforations in the drainpipe or the outlet become clogged. Also, many a footing drain has been damaged during a later modification of or addition to the structure. If the house has a footing drain, you should ask the owner to show you the location of the outlet. The drain outlet should be kept clear and should be checked occasionally during a heavy rain to ensure that it is operating properly.

Even though waterproofing the exterior surface of the foundation wall is more effective than treating the interior surface, quite often an interior treatment is chosen because of the costs involved in excavating around the foundation and temporarily relocating trees and shrubbery. For excessive water accumulation around the foundation, an interior treatment includes sealing the cracks and coating the walls to make them watertight and installing a drainpipe along the foundation footing below the floor slab that discharges into a sump pit.

Just a word about waterproofing the exterior surface of the foundation wall using a pressure-pumping process that requires no digging or relocation of plantings: Caution. In this process, a sealant, pumped through tubes that are inserted into the ground, is supposed to coat the wall and render it watertight. The effectiveness of this treatment depends on the condition and porosity of the ground around the foundation. Since contractors doing this work do not always take test borings and analyze the soil, the process is usually not effective, and additional measures are inevitably necessary.