Basement waterproofing

Basement waterproofing involves techniques and materials used to prevent water from penetrating the basement of a house or a building. Waterproofing a basement that is below ground level can require the application of sealant materials, the installation of drains and sump pumps, and more.
Purpose.
Waterproofing is usually required by building codes for structures that are built at or below ground level. Waterproofing and drainage considerations are especially important in cases where ground water is likely to build up in the soil or where there is a high water table.
Water in the soil causes hydrostatic pressure to be exerted underneath basement floors and walls. This hydrostatic pressure can force water in through cracks, which can cause major structural damage as well as mold, decay, and other moisture-related problems.
Methods.
Several measures exist to prevent water from penetrating a basement foundation or to divert water that has penetrated a foundation:
Interior sealants.
In poured concrete foundations, cracks and pipe penetrations are the most common entry points for seepage. These openings can be sealed from the interior. Epoxies, which are strong adhesives, or urethanes can be pressure injected into the openings, thus penetrating the foundation through to the exterior and cutting off the path of the seepage.
In masonry foundations, interior sealers will not provide permanent protection from water infiltration where hydrostatic pressure is present. However, interior sealers are good for preventing high atmospheric humidity inside the basement from absorbing into the porous masonry and causing spalling. Spalling is a condition where constant high humidity or moisture breaks down masonry surfaces, causing deterioration and shedding of the concrete surfaces.
Interior water drainage.
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 and recognized by BOCA (Building Officials and Code Administrators) as being effective in controlling basement water.
A common system for draining water that has penetrated a basement involves creating a channel around the perimeter of the basement alongside the foundation footers. A French drain, PVC pipe, or a patented drainage system is installed in the newly made channel. The installed drain is covered with new cement. According to Rick Jacobs of Absolute Waterproofing Solutions, a basement waterproofing and foundation repair company, states like Michigan have a lot ground clay, which will absorb and hold water, resulting in the flexing in basement foundation walls that can cause cracking and subsequent leaks. 
The drainage system collects any water entering the basement and drains it to an internally placed sump pump system, which will then pump the water out of the basement. FEMA recommends basement waterproofing with a water alarm and "battery-operated backup pump" as a preventive measure against the high cost of flooding. 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.
Interior waterproofing.
Interior basement waterproofing using coatings is effective where condensation is the main source of wetness. It is also effective if the problem has minor dampness. Usually, interior waterproofing will not stop major leaks.
Exterior waterproofing.
Waterproofing a structure from the exterior is the only method the U.S. International Building Code (IBC) recognizes as adequate to prevent structural damage caused by water intrusion.
Waterproofing an existing basement begins with excavating to the bottom sides of the footings. Once excavated, the walls are then power washed and allowed to dry. The dry walls are sealed with a waterproofing membrane, and new drainage tiles (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 can be sprayed directly onto a wall, are very fast curing, and are semi-flexible, allowing for some movement of the substrate.
Causes of water seepage and leaks.
Water seepage in basement and crawl spaces usually occurs over long periods of time and can be caused by numerous factors.
Warning signs of water damage.
Signs that water is seeping into a basement or crawlspace often take years to develop and may not be easily visible. Over time, multiple signs of damage may become evident and could lead to structural failure.
Foundation crack injections.
Foundation crack injections are used when poured concrete foundations crack either from settlement or the expansion and contraction of the concrete. Epoxy crack injections are typically used for structural purposes while hydrophobic or hydrophilic polyurethane injections are used to seal cracks to prevent penetration of moisture or water. Concrete is both strong and inexpensive, making this an ideal product in construction. However concrete is not waterproof.