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The Complete Modern Guide to Basement Waterproofing
Copyright © 1994 - 2011 by J. Scott Gallawa. All Rights Reserved Worldwide
CHAPTER 1
How and Why Does My Basement Leak?
Continued from Page 1
With cinder or cement blocks, the builder parges on one coat of sandmix cement (1 part Portland cement and 2-½ parts builder's sand), sometimes two coats are used depending upon local codes. This coat of sandmix cement covers the entire surface of the wall, from the footing up to the ground level (grade level). Poured concrete doesn't require parging. By itself, this coating would still allow water to penetrate the wall by means of a natural action called capillarity. This is a large word simply meaning “wick action.” Poured concrete and concrete products such as cement and cinder block cannot resist water penetration on their own. They are porous and absorb water like a sponge. Walls standing below grade are usually cementitious (made from cement products) and therefore require a waterproofing membrane placed over their exterior face in order to repel groundwater. This process of applying the waterproofing membrane is generally the weak link in the chain of construction steps that leads to so many water problems later in the life of the house.
The Membrane
Typically, the builder will spray or brush a very thin coat of liquid tar (and I mean thin, like the coat of paint on your car) on the walls once the cement coating has cured. The builder will then cover this thin asphalt membrane with a layer of plastic (6 mils) held onto the wall with a piece of furring strip tacked along the top of the wall at the grade level. Lamentably enough, this plastic, in my experience, goes on quite haphazardly. In many cases, as a result of construction mishaps, there are large rips and holes found in the plastic before the foundation is backfilled. This plastic should cover the surface of the below grade walls from bottom to top around the entire perimeter of the basement.
Backfilling
Before the foundation is backfilled, that is, before the dirt which came out of the excavation is bulldozed back around the house, filling in the area where the workmen stood, an inspection for rips in the plastic should take place. Unfortunately, this is not a common practice and even if it was, the next step in the construction process would negate such an inspection. What happens? Well, here's the rub—and it is a rub! Stones in the backfill soil are rubbing on and cutting the plastic, slashing through the paper thin tar membrane. That's right, these sharp-edged rocks (and any miscellaneous backfill material) are ripping the plastic and stripping areas of the wall of its tar membrane. This leaves the new wall beginning its life semi-defenseless against future water penetration. But that's not all!
As the bulldozer or backhoe pushes the excavated earth back around the newly built walls, something very important is happening—or not happening—depending upon your point of view. None of this soil is being tamped! Not one square foot is being compacted as it goes back. Obviously, the bulldozer or backhoe cannot maneuver into the backfill area until the soil has reached a close proximity to grade level, lest the heavy machine should tumble in.
Continued...
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Copyright © 1994 - 2011 by J. Scott Gallawa. All Rights Reserved Worldwide
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