Waterproofing Basement Walls Externally
While interior basement waterproofing methods are for the most part relatively easy and can be done by just about anyone, exterior basement walls waterproofing is much more involved and often requires additional equipment and labor. All of this adds up to additional cost. So why waterproof your basement walls from the outside? The answer is because exterior waterproofing is the only way of preventing water from penetrating the foundation walls and therefore preventing the damaging effects that water can have on building materials. Interior methods involve dealing with the water that has entered while exterior waterproofing prevents the water from entering in the first place. Furthermore, building codes often recognize exterior basement waterproofing as the only method of preventing the damage caused by the long term infiltration of water.
There are many options for waterproofing basement walls externally. One of the most effective is the installation of footer drains. Footer drainage, often referred to as tile drainage, involves the installation of drains around the perimeter of the foundation below the footer. Water in the ground surrounding the foundation finds less resistance to entering the drainage system than to entering the basement walls. The disadvantage to this system is the amount of excavation that's required around the foundation. It is costly and disruptive. External drainage is best installed at the time of construction. When it comes to existing structures, interior drainage is often employed because it's substantially less costly.
External barriers, or external sealants as they are called, often work well when combined with a drainage system. Sealants are usually asphalt or cement combined with a waterproof base. The base is usually rubber or some kind of polymer. Traditionally, rubber was the base of choice and polymer bases were regarded as lower cost, and lower quality, alternatives. Over the last several years, manufacturers have substantially improved polymer bases making them very effective foundation wall sealers. Polymer-based sealants offer many advantages. They are not affected by soil pH. In liquid form they are thin enough to be applied with a sprayer. Once cured they often have some flexibility so they can withstand shifts in the foundation walls without cracking, and most will last the lifetime of the foundation wall itself.
Another component of an external drainage system is a sump pump. A sump is simply a natural or artificially created low point where water will collect. A mechanical pump within that low point removes the water to a remote location away from the basement walls. A sump pump may be necessary if the climate where you live is particularly rainy, the water table is unusually high, or the geography of the landscape makes a gravity-driven remote drainage system impractical. Sump pumps can be installed above ground or below ground. An above ground sump pump is easier to maintain and service. However, it can also be an unsightly feature of the landscape. Furthermore, the depth of the basement within the surrounding ground may necessitate a below ground sump system.
Lastly, some consideration should be given to the diversion system. As mentioned in a previous article, the diversion system is the building's gutters and rain spouts. The job of the diversion system is not only to collect the rain water that accumulates on the roof of the structure but also to divert that water away from the foundation walls. Many rain spouts deposit water on the gound within a foot or two of the walls which is inadequate. A properly functioning diversion system will work in concert with the building's other drainage systems to remove rain water from the vicinity of the foundation walls.
External waterproofing while costly, yields a peace of mind that comes from the knowledge that the best waterproofing methods have been employed. The water is being prevented from entering the basement in the first place, rather than being dealt with once it enters. External waterproofing is well worth the investment to ensure a comfortable, water-free basement.