Trained Eye

 
 
 

Basement Repair Methods

Question:

These are the proposals that my daughter received for fixing the leaky basement in her house. The second and third companies listed recommended steel reinforcing for the inside basement wall as well. The first company thought that the wall would go back into place when the soil pressure was removed from the outside.

The first contractor proposes to chip and patch all cracks, snap-ties and segregated areas using hydraulic grout as well as placing a bead at wall/footing joint. Remove existing failed exterior weeping tile system and flush access lines to assure drainage to floor drains. After patching they will pre-treat wall, prior to applying "Blue-Skin" water proofing membrane and place waterproof mastic at all seams. Backfill excavated areas to 1 foot from grade with clean ¾ inch drainage stone. Place filter cloth on aggregate and place clay cap with topsoil dressing graded away from house.

The second company proposes to do the same initial preparation and then apply Daraweld bonding agent (or equivalent) to chipped out areas. Next they will apply Sika Grout 212 non-shrink hydraulic cement grout (or equivalent) to chipped out areas and a bead where wall meets footing. Apply a primer coat of Bakor 910-01 foundation coating (or equivalent) to exposed wall below grade. When 910 has cured, embedded fibreglass mesh in a thick coat of Bakor 710-11 fibre reinforcement coating (or equivalent) over entire exposed wall below grade. Install new polyethylene weeping tile and finally cover weeping tile with approximately 12" of 3/4" river wash stone. Cover river wash stone with filter cloth and backfill high enough to allow for settlement.

 The third contractor proposes a similar system to the previous one with a noted difference. Prior to back filling, they will install protection board on entire exposed wall before backfilling with clean drainage stone near grade followed with and a clay cap.

Of the three products proposed by the different contractors, what is the best product to use to waterproof a basement wall from the outside?

Answer:

To answer your question, all three systems should provide adequate protection for damp-proofing your daughter’s foundation wall below grade. The possible benefits of different membrane systems are debatable and vary depending on who you talk to. The relative effectiveness of the different materials is very difficult to test because of the nature of the repairs. Once installed, the new damp-proofing is not visible and will not be inspected unless they fail and the soil has to be re-excavated.

The second and third contractors you have cited are using a more traditional method of damp-proofing repair to the foundation. This is simply cleaning the foundation wall, patching the cracks and applying a bitumen-based (asphalt based) damp-proofing. They may also add a fibreglass mesh within the coating membrane to add strength. The third contractor also suggested installing a “protection board”, which is often rigid foam insulation, before backfilling. This should help prevent the new damp-proofing material from wearing away during backfilling and from soil and stone movement outside the foundation. I think this is a very good idea to ensure that the new damp-proofing is not disturbed and allowed to properly cure.

The difference between both these quotes and the first is the application of a “Blue Skin” membrane. This material is a rubberized sheathing with a thick self-adhesive coating. It is considered to be superior to paint-on or trowel-on coatings, but is relatively new in common use. The durability has not been tested in our area for several decades, like the other methods. The proponents of the previous method question the membrane’s ability to adhere to uneven concrete foundations. There are also other corrugated plastic membranes, that may be used in conjunction with either of these other methods, that allows added protection and small openings to channel water away from the concrete.

The key to any foundation repair, which is common to all three quotes, is replacement and flushing of the weeping tiles and backfilling with drainage stone. This is the element that will prevent excess water from collecting outside the foundation and ensure that the basement stays dry. The new exterior plastic weeping tile will function well, but there may be further damage to the old tile embedded in or below the basement floor slab. If the contractor does not make sure that the old tile is properly draining and intact, the repairs may not have the desired results. Often, these inner tiles are damage or collapsed and must be removed and replaced, along with the ones outside the foundation. This will require cutting the basement floor slab and inside excavation, which can be disruptive and very messy, inside the home.

Steel bracing inside the cracked foundation wall is dependent on the size and location of the cracks and the extent of damage. The first foundation contractor may be correct that this step is unnecessary, as the wall will recede somewhat when excavated, but he should not be the one determining this. Evaluation by a licensed structural engineer is required to determine the extent of failure and movement of the foundation wall. The engineer should be the person deciding whether bracing is required and will engineer and prescribe the proper size and location of the repair material, if needed