When we partially excavated the foundation on the north and south sides of the house to make room for forms, it was noted that some of the concrete was in pretty bad condition. How bad? It was crumbling to a depth of two to three inches in a few areas. Since the foundation was already partially uncovered it was decided that this was a good a time to repair things and waterproof a bit while we are at it. Working with three to four hired laborers each day, the excavation took four days.
The completed south side trench. I covered both trenches with tarps to keep out the weather.
The patching involved in foundation repair is a bit like dentistry. Here are the steps: (Time estimate is for DIY part-time work, not 9-5.)
1: Clean the existing concrete of adhered and intercalated soil. (One day)
2: Remove any large protuberances from the external surface. (One day)
3: Tap over the entire surface with a hammer. Areas that are excessively weak will be obvious. Remove them with the hammer drill. (One day)
4: Use a wire brush to remove loose concrete. (Two days)
5: Wash the face of the concrete with water. (One day)
5: Seal any cracks found with hydraulic cement. (One day)
6: Working from the bottom up, “parge” the external surface of the foundation with topping mix. This creates a new hard surface to accept waterproofing. (One week+ depending on the condition of the foundation )
7: Apply waterproof membrane to surface and then backfill. (At least two days)
The parging process itself (#6 above) is probably the toughest step. Thoroughly mixing each 80-pound bag of topping mix and getting it down into the muddy trench is physically brutal and for all the effort you only get one cubic foot per bag, not much for a wall that is 25 feet long. At max only about four bags can be mixed and placed by hand per day; after that, I need a couple of days of rest. The man-hours for the physical labor and subsequent recovery create the largest time sink for waterproofing. If done correctly it creates a strong, adherent coating that should last another hundred years. If rushed, a weak, leaky coating will result.
Removal of concrete ledge with a hammer drill. The concrete at that level was in good condition.
The wall after removal of the ledge and wire-brushing. Note the newly exposed aggregate ready to accept the first coat of topping mix.
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