Wet Basements

Published on February 5th, 2013 | by Henri

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Waterproofing compounds basement-moisture damage

Q.    The house I bought a few months ago has severe water damage in the basement; the block I live on is sloped and the house next door has about a three-foot elevation above mine, so it appears that the ground water level under my house is higher than all the houses up-slope. As a result, water has been seeping through all of the foundation’s cinder blocks on the up-slope side of my house.

The previous owner applied a black adhesive substance and pasted black tar paper from the inside of the basement. The cinder blocks are flaking and there are areas with a white powdery substance bulging on just about every cinder block on that side of the house, not to mention the mold and mildew that exist. In addition, someone apparently dug a trench about 18 inches wide around the periphery of the basement and filled it with concrete. Water is seeping through that too, and even after several hot sunny days that area remains damp.

There is a sump pump which is located at the down-slope side of the house; it only seems to work during extremely heavy downpours and does not seem to be of any use for the underground water that follows a heavy rain. That water appears to be what is seeping through the foundation only at the up-slope of the basement.

If you can offer any suggestions on how I can remedy this situation, I will be most
grateful.

A.    The previous owner made a mistake in attempting to waterproof the cinderblocks from inside. All it accomplishes is to allow water to accumulate in the cores of the cinderblocks from where it evaporates inside the house, potentially causing serious problems. It is probably impossible for you to remove the tar paper and the tar that was applied on the blocks.

The concrete-filled trench on the perimeter of the floor is likely an attempt to direct water to the sump pump through a perforated pipe buried below the floor. Obviously, this is no longer working.

The first thing to determine is whether the leakage is caused by surface water running down the slope from your higher neighbors or by underground water from a rising water table or a spring that swells in heavy downpours or long-lasting rain.

Leakage from surface water generally occurs quite soon after the heavy rain starts, whereas a long delay – sometimes of several days – is likely from underground water. You should first check the grade around the foundation and make sure that it slopes away from it, especially on the up-side. If that solves the problem, you are done.

However, in the case of an underground water problem, you can have the up-slope-side wall excavated and waterproofed from the outside, but to be successful this will also require that at least one of the side walls be excavated as well, and that a drain pipe be installed on the back and side of your sloping yard to a storm sewer, if there is one, or to daylight. Or you can have a curtain drain built between your house and the upside neighbor. A deep trench is excavated to the depth of your foundation and carried to one or both sides of your house. Black plastic is pinned to the side of the trench closest to your house.

Two inches of egg-size stones are laid on the bottom of the trench followed by a perforated plastic pipe that runs to daylight. The backfill is done with the same size stones, either to the top (a French drain), which will also catch surface water or to within a foot of the top. Landscape fabric tops the stones and top soil completes the job. This may cause a problem with your down-slope neighbors if the water adds to what they already have.

Another option is to have a basement waterproofing company drill holes in the bottom row of blocks and install a fiberglass gutter system that leads to the sump pump. If the pump is not sufficient, you may need to replace it with a submersible pump of higher capacity. Whatever system you choose will be expensive.

The white powder is efflorescence and it can be wire-brushed off.

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