External Excavation and Waterproofing

In addition to pressurized injection, external excavation and waterproofing is a viable, but expensive, way to stop water ingress through a poured concrete foundation. While external excavation and waterproofing is now considered to be an old fashioned, expensive and destructive way to stop leaks, there are times when this waterproofing repair method is the most appropriate. Usually, this method is used when waterproofing cannot be done from the inside of the home. Homeowners will opt for external excavation and waterproofing when the finished basement walls cannot be opened or accessed; this is often the case when there are leaks behind expensive finished wet bars, teak panelling, fireplaces, and built-in wall units.

External excavation and waterproofing typically refers to the waterproofing of an entire wall or some part thereof. External crack repairs are also done by excavating the foundation, in a relatively small area, at the crack location.

The illustration below shows the configuration of an externally waterproofed wall.

External excavation and waterproofing is a relatively simple process; the steps are as follows:

1. A determination is made with respect to the amount of external waterproofing that needs to be done;
2. The accessibility of the excavation area is reviewed;
3. The location for the excavated soil is established;
4. A call is made for the locates (location of known underground gas and hydro lines);
5. Adequate clearance for excavator access is required (usually 42" wide); therefore, it may be necessary to remove a fence post or other obstructions impeding excavator access (unless the excavation is to be done by hand);
6. Shrubs and bushes along the excavation area are removed;
7. The area to be waterproofed is excavated;

8. The wall to be waterproofed is cleaned with a wire brush;
9. A liquid rubber coating is applied to the wall (this type of coating is much more elastic than an application of tar);
10. The existing weeping tile, within the excavated area, is removed and a new weeping tile is installed and connected to the existing system around the unexcavated walls;

11. The proper functioning of the weeping tile system is tested;
12. A gravel layer is installed on top of the newly installed weeping tile;

13. An air-gap membrane is installed over the rubber coating; and

14. The excavated area is backfilled.

It is important to note that there are inherent risks associated with external excavation and waterproofing; such as:

1. If improper excavation practices are used, there is the risk that a worker may be injured or killed by a soil cave-in; (the deeper the dig, the greater the risk)
2. The failure to obtain locates could result in significant damage to gas and hydro lines which could even result in an explosion;
3. The installation of the weeping tile must be done properly; if not, proper drainage will be impeded; and
4. The failure to protect the ground where the excavator travels can result in higher landscaping restoration costs upon completion of the waterproofing work.

Factors affecting the cost of excavation:

1. Digging by hand is more expensive than digging with an excavator;
2. Hand digging under a deck is a very expensive proposition;
3. The length and depth of the excavation are the primary determinants of the cost;
4. The need for a corridor dig (where soil must be transported by wheelbarrow to the front or back of the home because there is no room to pile the soil near the excavated area) adds significant cost;
5. The need to cut and/or remove and dispose of poured concrete or asphalt covering the area to be excavated adds cost; and
6. The cost of landscaping once the waterproofing work has been completed.

Note: Prior to the start of work, it is crucial that you confirm that the locations of the underground utilities are known, that the waterproofing contractor has at least $2,000,000.00 of commercial liability insurance, and that the workers have Workplace Safety and Insurance Board (WSIB) coverage. Also, most municipalities require that the waterproofing contractor have a Master Drain Layer on staff, in order to be able to offer external waterproofing services to the public. Call AquaGuard Injection & Waterproofing™ today at 1.888.284.2384 to have your waterproofing work done properly and safely.