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Waterproofing is needed anytime a structure is built at ground level or below ground. Waterproofing and drainage considerations are especially needed in cases where ground water is likely to build up in the soil and raise the water table. This higher water table causes hydrostatic pressure to be exerted underneath basement floors and against basement walls. Hydrostatic pressure forces water in through cracks in foundation walls, through openings caused by expansion and contraction of the footing-foundation wall joint and up through floor cracks. Hydrostatic pressure can cause major structural damage to foundation walls and is likely to contribute to mold, decay and other moisture related problems.
The three measures developed to prevent this problem differ greatly in ideology and design. The three methods are:
In poured concrete foundations, cracks and pipe penetrations are the most common entry points for seepage. These openings can be readily sealed from the interior. Epoxies or urethanes are pressure injected into the openings, penetrating the foundation through to the exterior, thereby cutting off the path of the seepage. These repairs will last for a long time. Many contractors provide 10 year to lifetime warranties on these repairs.
In masonry foundations, interior sealers will not provide permanent protection from water infiltration where hydrostatic pressure is present. Interior sealers are good for preventing high atmospheric humidity inside the basement, from absorbing into the porous masonry and to prevent spalling. Spalling is a condition where constant high humidity or moisture break down masonry surfaces causing deterioration and shedding of the concrete surfaces.
When the foundation is constructed of concrete blocks, an interior drain tile system, described below, can capture the water entering the block system and drain the water into a sump. Typically, weep holes are drilled into the lowest course of block, allowing the drainage to occur. This system will provide a dry and moisture free basement for years to come.
Although interior water drainage is not technically waterproofing, it is a widely accepted technique in mitigating basement water and is generally referred to as a basement waterproofing solution. Many interior drainage systems are patented as well as recognized by B.O.C.A (Building Officials and Code Administrators)as being effective in controlling basement water. They function by draining underground water from alongside the foundation footers and underneath the basement floor. They then channel it with a French drain, PVC pipe, or through a patented product to a sump pump system, which will then pump the water from the basement. Wall conduits such as dimple boards or other membranes are fastened to the foundation wall and extend over the new drainage to guide any moisture down into the system. Foundation sump pumps can be installed through do-it-yourself kits, plumber installations, or by a professional waterproofing contractor and generally come in plastic and cast-iron models.
Interior basement waterproofing systems should be prepared to work in the case of a power outage, the failure of a sump pump, and in the face of overwhelming torrential rain. A proper sump pump, backup sump and/or battery backup sump pump should be installed in a large sump pit with an airtight lid for safety and to keep humidity from seeping through to the basement environment, where it can promote mold growth. This airtight practice will also reduce the possibility of dangerous radon gases for entering the living space.
Basement waterproofing inside, using coatings, works well where condensation is the main source of wetness. It is also quite effective if the problem is minor dampness. Major leaks can’t usually be handled by inside coatings. In such cases, if outside waterproofing has been ruled out, your best inside basement waterproofing solution will probably be sheet or tile coverings which conceal drainage structures to carry the water out and drain it from the home.
Exterior waterproofing prevents water from entering foundation walls therefore preventing the wicking and molding of building materials. Waterproofing a structure from the exterior is the only method the IBC (International Building Code) recognizes as adequate to prevent structural damage caused by water intrusion. Prior to the 1980s much of the original exterior waterproofing was actually damp-proofing using a degradable asphalt-based covering. Waterproofing an existing basement begins with excavating to the bottom sides of the footings. Once excavated, the walls are then sealed with a waterproofing membrane and new drainage (weeping tiles) are placed at the side of the footing.
Over the past ten years, polymer-based waterproofing products have been developed. Polymer-based products last for the lifetime of the building, and are not affected by soil pH. Polymer-based waterproofing materials have the advantage of a low enough viscosity that they can be sprayed directly onto a wall, are very fast curing, and are semi-flexible, allowing for some movement of the substrate.