Leaking Basements (Assessment & Solutions)
A leaky basement can be a common problem for structures close to a body of water where the water table is typically high (sea, lake, underground reservoir). The long term damages can affect the integrity of your structure and ultimately result in costly repairs. We will explain what are the main causes of water-related problems in basements, how to properly inspect, assess the damages, and provide some effectively repair methods.
CAUSES OF LEAKS
Water in the basement can come from the inside of the structure, as in a broken plumbing or condensation; however the most common source of seeped water comes from the external perimeter of the foundations, due to rainfall and ground water. This manifests in four different ways:
Hydro-static Pressure – when the water table rises under a foundation it creates hydro-static pressure against the foundation from below that can force water into the basement.
Lateral Pressure – when soil around the foundation expands, it creates lateral, or sideways, pressure against the walls that can cause foundation damages and create leaks in the basement.
Differential Settlement – when the foundation settles unevenly due to different subsoil properties, it will create diagonal cracks on the walls and joints where water can leak from.
Capillary Absorption – when porous concrete is used for the foundation, ground water can penetrate the concrete walls and travel all the way to the interior through capillary action.
Failure in waterproofing system - when installed waterproofing membranes are improperly placed, mishandled, or punctured. Or even when the whole waterproofing system design and detailing is primitive and inappropriate. This will ultimately lead to the ingress of water underneath the membrane after water table rises. However, water tightness is not only related to the waterproofing system installed but also to the overall concrete quality: more specifically the concrete itself and joint preparations. Thus, an excellent waterproofing system at place would be ineffective if concrete quality is compromised. Consequently concrete mix design and w/c ratio, concrete handling/placement/curing methods are extremely important in achieving water tight concrete.
INSPECTION & ASSESSMENT
Identifying basement leaks in a timely and professional manner will be crucial in order to prevent further damages to the structure, and to recommend the optimal remedial works. The main objective should be to determine the source of the water, stopping it and assess the extent of damage on the concrete (short and long term). Starting with a thorough revision of documents, drawings and records related to concrete quality/design, layouts and details of construction and expansion joints as well as records of the installed waterproofing system. This usually helps in providing a better understanding about the case at hand and pin point on specific faults at the design stage.
A second step would be conducting a visual inspection, to look for signs that indicate leakages:
Dampness or brown stains on walls
Mold and mildew
Chipped and delaminate concrete
Next we use a series of non-destructive tests to optimize the visual inspection, and to assess more profoundly the damages that might have occurred to the reinforced concrete due to the leaking:
Thermal Imaging – to locate on a large scale damped walls and moist areas. Can be very advantageous in dark/low light areas.
Ultrasonic NDT using either UPV, Impact Echo or Impulse Response – to determine locations and extent of delamination, voids, and cracks as well as locating any lower quality or porous concrete spots in the foundation that may be the cause of leaking.
Half-cell Potential and Corrosion Rate Measurement – since steel corrodes in presence of water and oxygen, it is important to evaluate the rebars and determine the rate of corrosion as well as measure the resistivity of concrete for potential corrosion.
Lastly we will extract concrete core samples to determine important physical properties, and to verify and confirm non-destructive findings. The following are some the recommended tests:
Density, absorption, and voids in hardened concrete (ASTM C642)
Depth of penetration of water under pressure (BS EN 12390-8)
Water absorption (BS 1881 - Part 122)
When the source of the leak has been identified, and the damages were evaluated, then the repair methods can be recommended accordingly. Note that each case is unique, and not all repair solutions will deliver the same results. Nevertheless, here are some common repair practices:
For floor cracks and cove seepage, the secret is first to alleviate the hydrostatic pressure by giving ground water somewhere else to go. This is accomplished by installing an internal drainage system that directs the water away from the foundation. Next, floor cracks needs to be sealed and that is done by injecting high pressure epoxy to fill the gaps.
For a wall crack, the most common way of repair is to inject it from the interior or exterior with expanding polyurethane. The polyurethane fills and seals the crack out to the soil and stays flexible when cured to prevent minor foundation movement from re-opening the crack.
For concrete deterioration or initiation of corrosion at the rebars, the concrete and the reinforcing steel need to be treated and repaired. This can include removing of concrete cover, wire brush all the corroded rebars, apply anti-corrosion coating, and recast using a special mortar.
The way to repair seepage permanently from mortar joints, porous walls or over the top of a wall is to install an exterior waterproofing membrane. But this is a costly method because the perimeter of the exterior needs to be exposed, thus the need remove all the soil around the foundation.
Wise Cracks. “5 Causes of Leaks in Your Basement & How to Find Them”.http://www.wisecracks.com/5-causes-leaks-basement-find/[viewed on November 15, 2018].
U.S. Waterproofing. “Why a Basement Leaks and How to Fix it Permanently”. https://www.uswaterproofing.com/learning-center/why-a-basement-leaks-and-how-to-fix-it-permanently [viewed on November 15, 2018].
http://www.basementsystems.ca/basement/waterproofing/problems/wall-leak.html [viewed on November 16, 2018].