Basement leaks through a concrete block wall – nusite waterproofing contractors

Many homes in Toronto and the surrounding GTA have poured-concrete foundations, but some of them are made of concrete block, which is often referred to as concrete masonry units (CMUs) or cinder blocks. The walls of concrete block foundations sit on a footing which is a concrete-poured pad that is wider than the building’s foundation wall. This helps to distribute the home’s weight load. The foundation’s construction starts with pouring the footing inside a trench which contains metal or wood forms. The footing needs to sit lower than the freeze line and possibly deeper if there’s going to be a full-height basement.

The footing’s thickness and width depends on the construction and size of the home as well as the soil’s load-bearing capacity.


During the basement excavation, the first row of concrete block is laid on the footing when it has cured to describe the structure’s perimeter. For foundation walls, the typical thickness of the concrete block is eight inches. However, foot-thick blocks are sometimes used for heavier loads and higher walls. More courses of block and mortar are added in a brick-like pattern until the proper height is reached. At this time, any openings and windows are built and the mortar in the wall is given time to cure.

If there are hollow cores in the block walls they may be filled completely with mortar, but usually the edges of openings and corners of the wall are filled. In addition, extra strength may be added with steel rebar. Once the walls are finished the basement floor is poured with concrete and the ground floor framing is completed. The foundation is now supported at the bottom and top and it’s backfilled and compacted with soil while construction begins above the ground.

Poured-concrete and concrete block foundations both have identical load-bearing strength, but concrete block walls are more susceptible to any type of lateral pressure which can result in seepage problems. This is because water can seep into a basement through concrete block walls via the porous blocks and any cracked mortar joints. It’s recommended that you waterproof a home’s block foundation by installing a waterproofing membrane to the exterior. This method can be done while the building is being constructed or by excavating around it.

The exterior membrane consists of asphalt-modified polyurethane. It’s applied in a thick coating to the exterior of the foundation walls and it created a barrier which helps keep out water. The waterproofing membrane is different than a damp-proofing spray as the spray is a thinner liquid which is sprayed over foundation walls when the home is built to keep condensation out of its interior. The membrane can be improved with exterior drain tile when the water table is high. The drain tile is designed to carry ground water away. In addition, drainage board can be installed on the walls as a method to help protect the exterior membrane by channeling the water downward.

No matter what the reason is for your damp basement, if you have a concrete block foundation that needs to be waterproofed please feel free to contact our team of professional contractors at Nusite. We have over 30 years of experience dealing with concrete block walls in the GTA and will gladly schedule a visit to your home for a free inspection and estimate.