Replies

1. Expert Member
   MALCOLM TAYLOR | Apr 14, 2013 08:43pm | #1

   Mary, there are essentiality three ways to effectively waterproof a foundation wall from the exterior. One is to apply sealant such as Xypex that crystallizes in the presence of moisture. The second is to apply a spray-on elastometric coating and the third is to place plastic perforated sheets such as Dimplex to carry the moisture down to your perimeter drains.
   Unfortunately all of these require you to completely expose the wall down to your footings.

2. 
   user-1140531 | Apr 14, 2013 08:44pm | #2

   Mary,

   If you have not yet dug up your basement, I suggest re-grading the yard and do everything possible at the surface to mitigate the water problem. The tar products and similar exterior treatments are basically to stop the wicking of ground moisture, which is always present even if there are no actual water problems. Concrete absorbs moisture like a sponge, so a concrete basement will always have dampness in the walls if the wicking from the ground dampness is not blocked. So that is what the damp proofing tar does.

   Almost any time the ground surface slopes toward the house, it will cause actual water problems, and damp proofing will not prevent them. Another common cause of water problems is roof drains discharging to close too the foundation.

   If the ground slopes toward the house from a long distance such as across several adjacent yards, the remedy is to create a swale in your yard that intercepts the surface water heading toward your house, and then pitch that swale to carry the water to lower area nearby. So beginning at your basement, the ground will slope downward as it approaches the lowest point in the middle of the swale. Ideally, the centerline of the swale will be at least 25 feet away from the basement so the water will not get too close before being intercepted by the swale.

   If you can achieve a downward slope away from the basement all around, it will probably eliminate your water problem. In addition to the slope, it helps to compact the ground all around the basement so that rain falling directly in that area will run off on the surface. Some people have soft cultivated ground with plants right next to their basement, and sometimes this ground has even settled into a bit of a pocket due to the initial settling of the basement backfill.

   If you don’t fix the surface slope of the ground, the only remedy associated with excavating the basement is to install a drain tile. If you did that, you would damp proof the basement in the course of the work. But damp proofing without fixing the slope and/or installing a drain tile will probably not help. And damp proofing may not be necessary if you fix the slope.

   Although surface re-grading is the best solution, whether it can be done will depend on the existing elevations, location of trees, etc. So those conditions must be assessed to work out a swale strategy.

3. GBA Editor
   Martin Holladay | Apr 15, 2013 06:08am | #3

   Mary,
   The most important element in any waterproofing system is a functioning footing drain. As Malcolm points out, that requires you to excavate the exterior of your foundation down to the footing. In addition to the footing drain and associated elements -- crushed stone wrapped in a burrito of landscape fabric -- you need somewhere to convey the water to. If you can't drain to daylight or a municipal drain of some kind, you may need to drain the footing to an interior sump. (This is not ideal, but it is sometimes necessary.) Of course, that raises the next question: where do you drain the sump to? Some municipalities allow you drain sumps into sewer pipes; others don't.

4. 
   user-1140531 | Apr 15, 2013 10:49am | #4

   I agree that a footing drain will solve the water problem even with the surface conditions directing water toward the foundation. However, many houses have been built without footing drains and do not have water problems. So it is possible to correct a water problem by re-grading rather than digging up the basement. That could be a cost saving of 90%.

   Houses with footing drains and improper surface slope often still have water or excessive dampness issues due to the footing drain either being overwhelmed or partially plugged due to heavy use and/or poor installation. And the excessive surface and backfill wetness that a drain tile might mitigate will still tend to result in excessive frost heave, which itself can result in structural problems with sidewalks, deck footings, etc.

   Solving the problem in total is often a matter of optimizing several details. I bought a house that seemed to have a water intrusion issue in the basement, so I excavated the entire foundation down to the footing. I discovered buried trash in the area where water seemed to be penetrating the wall. I found an empty 55 gallon drum buried in the backfill as trash. It was in contact with the wall, empty of any dirt, and half full of water that had drained down and collected in it.

   I put in a complete drain tile system, imported proper fill sand, compacted the new backfill, and detailed the surface with fabrics and proper slope.

   I am sure that no water has ever entered the drain tile, but it is there as a backup. The problem in that case was the buried trash, so excavation was required to remedy it. However, I did not know that starting out. Cleaning out the trash and refilling that one spot probably would have solved the entire problem. But I had half the foundation dug up before I found the trash.

5. Expert Member
   MALCOLM TAYLOR | Apr 15, 2013 11:09am | #5

   Ron, a lot of the excavations I've done on sloped sites have water seeping through seams on the excavated dirt walls regardless of the surface grading. You are right that re=directing surface water away from the house is an essential first step, but it's not always going to solve the problem.

6. 
   Andy_Engel | Apr 15, 2013 02:45pm | #6

   It really does depnd on the site. In the northeast with our glacial soils, it's not unusual to find a layer of hardpan soil somewhere between the surface and the level of the footings. In these cases, adjusting the surface drainage may not completely fix water problems (although it's excellent practice!). The hardpan is essentially impervious to water, and it might be collecting water from hundreds of acres above the house. I've literally seen underground rivers in these conditions even though the adjacent surface was properly graded. In these cases, footing drains are a must. Now, I don't think you find much hardpan in DC (hard heads, maybe, but not hardpan), but I think high water tables are pretty common. Similar to hardpan conditions, you can end up with a lot of water at the footing level that's mostly unrelated to the surface grade. So, yes, footing drains matter there. And because of the flat topography, it might be difficult to drain them to daylight, so an internal sump and pump to the storm sewer or at least to ground 20 feet or so downhill from the house might be the way to go.

7. 
   user-1140531 | Apr 15, 2013 03:13pm | #7

   One condition that surface grading will not remedy is water moving down grade below the surface, as can be found on hillsides. I looked at some houses in Hancock, Michgan where a large portion of the town is perched on a very steep and long hillside. One of them was reported to have a creek running through the basement.

   If I were building a new house, I would put in a footing drain tile as a matter of course. And then I would compact the backfill and detail the surface as well. If your elevations preclude daylighting the tile, you can put in a large dry well to accept the drainage.