In an earlier article, we wrote at length about the ways in which masonry foundation walls encounter problems with water seepage and suffer structural damage. To recap:
Seepage problems usually occur in masonry walls for two reasons. One is that masonry walls have hundreds of feet of mortar joints where the masonry units are held together. These mortar joints can deteriorate over time or can crack fairly easily from minor foundation movement. Water then finds its way through the mortar joints into the basement.
Another common reason stems from the masonry units themselves. The stone and fired clay brick used in older masonry foundations were (and remain) pretty impervious to water, as were any ceramic product such as telephone tile. The most common masonry unit in use today is the concrete block, often called a “cinder block,” which does not have the same level of ability to hold out water.
Concrete blocks are molded out of a concrete mix that uses a fairly coarse aggregate in order to keep the blocks light and hold down the cost. These blocks perform well in maintaining a stable foundation but contain so much Portland cement and so many spaces between aggregate particles that they are naturally fairly porous.
Water can seep through the outer wall of the block, collect in the cavities and take its time seeping through the inner wall into the basement.
Structural damage to masonry foundations occurs because of the soil outside the foundation and happens in one of two ways.
When soil surrounding the foundation becomes oversaturated due to heavy rain, snowmelt or poor water management outside the home, it swells and creates pressure against the foundation walls. When this pressure reaches a sufficient level, it can exert enough force to make the wall bulge or bow inward in the center. If the damage is left unrepaired, blocks can actually be pushed out of the plane of the wall.
This damage can force the wall to separate from the structure it supports and create instability throughout.
In the other case, the problems stems from the opposite occurrence. The foundation was originally built on undisturbed soil that was very compacted so that it supports the foundation with minimal movement. During times of drought, trees and large shrubs near the foundation will extend their root systems downward and outward in search of water and can draw water from the soil under the foundation.
When this soil is desiccated it shrinks and withdraws its support from the foundation, causing the foundation to settle or sink. This will also cause the foundation to separate from the aboveground structure and can cause severe damage throughout the home.
Whether the damage to a masonry foundation creates a seepage or structural problem, the good news for homeowners is that both can be repaired.
Fixing Seepage Problems in a Masonry Foundation
Seepage problems in a masonry wall can either be repaired or managed, depending on the homeowner’s needs and his or her use of the basement.
Unlike cracks in a poured concrete wall, cracked mortar joints cannot be injected or otherwise repaired individually. Because the injected polyurethane would not expand out to the soil on the exterior, the crack would not be fully sealed and lateral pressure might force seepage through despite the repair.
Also, attempts at repairing porous masonry from the inside, such as the use of “waterproofing” paint or sprays, are at best short-term fixes as water will accumulate under these coatings and ultimately cause them to peel off the wall.
The best method of permanent repair for a seeping masonry wall is to install an exterior waterproofing membrane, a thick coating of asphalt-modified polyurethane that is spread on the outside surface of the wall.
To install an exterior waterproofing membrane, the foundation must first be excavated, usually all the way down to the footings, leaving a trench large enough for the installer to work. The work begins by thoroughly cleaning the wall surface of soil and debris to improve adhesion.
Once the wall is clean, the installer uses a trowel to spread a thick coat of the polyurethane material, which will cure and form an impermeable membrane that is especially formulated for underground use. The membrane may be covered with insulating material to keep the chill out of the basement and/or by dimpled, heavy-duty plastic drainage board that will protect the membrane and channel water downward.
Quite often, homeowners who have significant groundwater issues will complement the waterproofing membrane by installing exterior drain tile. This is a system of perforated PVC pipe that is buried in a bed of washed gravel to promote drainage. The pipe, which is also wrapped in a “sock” of filtration fabric to keep out debris, picks up the ground water and carries it off to a sump pump for discharge from the foundation.
Once the installation is complete, the excavation is backfilled and the repairs are invisible from the outside.
A homeowner may also choose to simply manage the seepage through a masonry wall instead of doing extensive exterior repairs.
“Managing” the seepage means allowing the water to continue to come through the wall and run down to the bottom where it will flow into a specially installed interior drain tile system.
Interior drain tile is a system similar to its exterior cousin except that it is made of flexible, corrugated plastic pipe that is also perforated. Interior drain tile is installed in a bed of washed gravel beneath the basement floor around the perimeter and is normally used to relieve hydrostatic pressure under the foundation and eliminate seepage through floor cracks or the cove joint.
When intended to capture wall seepage, a small gap is left when the basement floor is replaced to allow wall seepage to reach the drain tile. This gap is covered by a specially designed cove molding (or baseboard) that covers the opening to keep out dirt and debris but allows the flow of water.
The homeowner may choose to also install a vapor barrier on the wall to contain and cover the seepage.
Fixing Structural Problems in a Masonry Foundation
When a masonry wall is pushed inward by lateral pressure from oversaturated soil, the wall becomes unstable and threatens the entire structure. It is possible to shore up the house, demolish the wall and rebuild it but this extensive repair is very seldom necessary. The preferred method is to stabilize the wall in place to prevent any further damage.
If the homeowner catches the damage early on, the repair is simpler and less costly. If the movement of the wall at its farthest point is less than two inches the wall can be stabilized with carbon fiber strips.
Engineering data is used to determine the number and placement of strips to stabilize the wall permanently. To begin installation, the technician grinds down the area where the strips are to be placed to flatten it and improve adhesion. He then uses an industrial-strength epoxy to secure the 12-inch wide strips to the entire height of the wall. The strips are secured to the framing above and the wall is stabilized.
Carbon fiber repair can be painted over and it leaves only a slightly raised profile on the wall.
If the inward movement of the wall has exceeded two inches, then carbon fiber is no longer a viable repair approach. Instead, the foundation repair contractor will use low-profile steel channels to stabilize the wall.
The steel pieces are bolted to the foundation footings beneath the floor and placed along the height of the wall. They are attached to a bracket mounted between the floor joists above and tension is applied to tighten them against the wall. Once the steel channels are in place the wall is stabilized and the repair is maintenance free.
The profile of the steel channels is low enough to be covered by a standard 2” x 4” stud wall if the basement is to be finished.
If soil desiccation and compaction have caused a masonry foundation to drop, sink or settle, the only effective, permanent repair is to raise the foundation (and the house) back to its original level and stabilize it there.
The most effective method of doing so is to use a system of steel hydraulic push piers. An engineer will study the problem and recommend the number and placement of piers to stabilize the foundation permanently.
To install hydraulic push piers, technicians first excavate down to the foundation footings at the sites of the piers. The footings are notched and a steel bracket is bolted on.
Sections of steel column are then inserted through the bracket and driven into the earth by a hydraulic ram until the column reaches a load-bearing stratum below ground. Once all the piers are in place, hydraulic lifts are attached and a large hydraulic pump is used to lift the foundation back to level.
When the foundation has reached level, each column is bolted into the bracket and the house is stabilized. The excavations are backfilled and the repair is invisible and maintenance-free.
When a homeowner with a masonry foundation discovers seepage problems, he or she will need the advice and services of a professional basement waterproofing contractor. If structural damage is found, a foundation repair company is needed. At U.S. Waterproofing, our basement waterproofing team has stopped seepage in thousands of masonry basements during our 57 years in business. Our foundation repair experts utilize engineering data and the latest repair techniques to stabilize foundations quickly, permanently and cost-effectively. Why not ask for our free advice when you have a problem?