20 August 2005
A. Leaking basement walls are probably the most common problem homeowners wrestle with especially around here and especially during summers with intermittent downpours. When your house was built the builders placed a perimeter trench drain around the in side of the basement walls down near the footers and then approximately four inches of pea gravel was placed over the whole floor and then the concrete, also about 4 inches thick, was poured on top of that.That was in the code then and the County or City inspectors had to come out and look before you could pour the basement.
What appears to have happened in your case is the concrete pour of the floor ended sitting right on top of the concrete footing and tight against the bottom of the lowest course of foundation block. That has effectively created a seal at the bottom of t he wall and water that enters the hollow cores of the block canít work its way down to filter out at the bottom block course into the gravel then into the perimeter pipe and off to the sump. Thatís why you donít see any or much water flowing through tha t black plastic pipe but you do see it flowing out onto your basement floor. Thatís frustrating.
Donít you do this unless you have a plan in place but I have taken a hammer and driven a hole into the block just above the floor level only to have water shoot out from the inside of the foundation wall like a hose to prove the point that water was stan ding inside of the block wall. The contractors who want to cut in a new interior perimeter drain would perform a variation on this theme.
Your thinking about intercepting the water before it gets inside the wall is to my thinking the smartest approach. The old asphalt coating that you say is gone was intended as damp-proofing and it never really worked but was required. But adding a sheet drain system at this stage of the game would require excavation down to the footers all around the foundation. That can and will be both messy and expensive and itíll work. That technique was developed to de-water commercial buildings that went many fe et into the ground and the hydrostatic pressure of the ground water had to be intercepted.
The approach Iíd suggest you take begins very elementally and starts with making sure your gutters and downspouts are in fact doing their jobs and any rainwater that hits your roof is directed away from the house. That goes too for the grade around the f oundation. We like to see a drop in elevation of the dirt against the foundation wall at a rate of an inch or two per foot for about six feet away from the wall.
The take a hard look at your landscapping. A 20 year old house has had time to grow some pretty monstrous bushes near the house that prevent good drainage. Get rid of them if you must. Piling up mulch sometimes hides poor drainage so check that if youír e a mulcher. Donít give up on those old ďFrenchĒ drains. Re-excavate and clean them out. This time when you fill them back with gravel be sure you place a layer of filter cloth over top to prevent the sand clogging. Try all this before you go throwing tons of money at contractors, sheet drains and messy excavation.