Excavation and Waterproofing

In addition to de-watering, water ingress through a concrete block foundation can be remedied by excavating and waterproofing the exterior walls.

Note: Pressurized injection techniques cannot be used on concrete block foundation walls as it is not possible to control the containment of the injection resins.

While external excavation and waterproofing is more expensive than de-watering, there are instances when external excavation and waterproofing is the most appropriate solution for a leaking concrete block foundation:

1. In many cases, external excavation and waterproofing is used when de-watering 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;
2. The exterior condition of the concrete blocks may dictate that further deterioration of the concrete blocks must be arrested if the integrity of the foundation is to be maintained;
3. The liquid rubber membrane, applied to the exterior wall during the external excavation and waterproofing, prevents the foundation wall from coming into contact with ground water. As a result, the concrete blocks will not absorb water; this is significant when dealing with concrete blocks above the frost line. Water soaked concrete blocks that are exposed to freezing temperatures will deteriorate rapidly as they tend to spall;
4. Although internal de-watering will keep your basement dry, water continues to penetrate the concrete blocks due to their exposure to constant hydrostatic pressure. While de-watering will drain the water to the sump pit/liner, the exterior walls are not protected as discussed in point 3 above;
5. External excavation and waterproofing involves the replacement of the weeping tile along the excavated area and provides you with an opportunity to remove sediment and roots which may be clogging the weeping tile along the unexcavated sections of the foundation;
6. External excavation provides an opportunity to straighten a bowed foundation wall; and
7. When performing external excavation and waterproofing the installation of a cleanout is generally included (this allows easy access to the weeping tile from above grade in order to clean out clogged weeping tile).

It is clear that there are many advantages to external excavation and waterproofing of a concrete block foundation; however, there are also some disadvantages:

1. External excavation may require the removal and re-installation of a deck, patio, driveway, cabana, flower bed, or concrete walkway;
2. Excavated soil tends to settle over prolonged periods of time (usually a few years). This makes driveway, patio, and walkway re-installation problematic as they will likely slant towards the home as the soil settles;
3. Trees, shrubs and bushes that have been growing for many years are often damaged or destroyed;
4. Re-landscaping upon completion of the external excavation and waterproofing work is often necessary;
5. Air conditioning units, pool filters, and hot tubs along the excavation need to be disconnected, removed, and re-installed;
6. The installation of carbon fiber reinforcing straps, to arrest horizontal cracking in the mortar joints of the block foundation wall, cannot be installed on the exterior side of the foundation walls.

The illustration below shows a properly waterproofed concrete block foundation 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 wall to be waterproofed is excavated;

8. The wall to be waterproofed is cleaned with a wire brush;
9. Cracked mortar joints are tuck pointed;
10. The entire exposed foundation wall can may be covered with a parge coat (this will be dictated by the condition of the concrete blocks and involves additional cost);
11. A liquid rubber coating is applied to the wall (this type of coating is much more elastic than an application of tar);
12. 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;

13. The entire weeping tile system is tested for proper operation;
14. A gravel layer is installed on top of the newly installed weeping tile;

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

16. 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;
6. Air conditioning units installed along the area to be excavated need to be removed, the refrigerant needs to be captured, and the unit needs to be re-installed using a bracket fastened to the wall; and
7. 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.