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Masonry Foundation Problems – Seepage and Structural Damage

Sep 28, 2014 • By Matthew Stock.

How to Waterproof a Concrete Block Foundation in Northwest Indiana

For centuries, humans have set stone on top of stone to build structures.  Ancient European cathedrals, the pyramids of Egypt and the Inca, Mayan and Aztec ruins of the Americas are testimony to that.

When Europeans arrived on the shores of North America and began to build permanent homes and public buildings, the plentiful stone of the Northeast enabled them to build stable bases for the structures – rubble foundations at first, followed by longer-lasting stone foundations held together with mortar.

Until concrete became the preferred building material, homes in the United States were built on masonry foundations constructed of stone or brick.  In some parts of the country, including the Midwest, a webbed terra cotta block, known as “telephone tile” was sometimes used.

Later, concrete blocks, formally known as “concrete masonry units” (CMU) but often called “cinder block,” became the masonry material of choice for both foundations and aboveground construction.  CMUs are still used for foundations today, especially in areas that are too far from a concrete plant to make delivery of wet concrete practical or cost-effective.

Concrete block makes for a very stable and strong foundation, as capable as poured concrete of supporting and stabilizing a home of any size.  Like any masonry work, it requires the attention of a skilled mason to be built properly and often needs to have corners and other vulnerable areas reinforced with rebar and poured concrete.

All masonry foundations are prone to some problems, both structural and non-structural that are contributed to by their non-monolithic structure and numerous mortar joints.

Masonry Foundation Problems – Seepage Issues

All foundations can seep water through the cove joint or through cracks in the basement floor, with water being forced into these openings by hydrostatic pressure.  Similarly, any foundation can experience seepage over the top of the foundation wall when grading problems or improperly sloped exterior improvements – sidewalks, patios or decks – cause water to run back toward the house instead of flowing away.

Window wells with clogged or missing drains or separated liners will also cause seepage in any basement regardless of construction.

There are two factors that contribute to seepage in a masonry wall beyond the ones that can impact any basement in any type of foundation. 

Porous masonry materials – The materials used in masonry can contribute to seepage if they are porous enough to allow water to seep through, even if it takes a very long time.

Typically, stone used in foundation masonry is not porous and generally won’t admit water.  The relatively uncommon telephone tile (or any ceramic masonry unit) will be less porous if it is glazed; unglazed terra cotta is slightly more porous.

Very old brick foundations that may have been constructed of unfired clay brick will be relatively porous, especially when compared to the more modern fired clay brick that is good at keeping water at bay.

The real culprit in masonry foundation porosity, however, is the modern CMU or concrete block.   Concrete is, in general terms, a mixture of Portland cement and aggregate and depending on whether  a coarse or fine aggregate is used and the amount of cement in the mixture, the concrete block will be more or less porous.

Adding to the problem is the design of the block itself, having two large cavities inside the concrete web.  The air space created by these cavities does provide a degree of insulation and the openings make the block lighter but do not compromise its structural strength.  These cavities can fill slowly with water if it seeps through the outer wall of the block and that can create seepage through the inner wall into the basement that can occur in the absence of rain or snow.

Mortar joints – The other weak point for seepage in a masonry wall, which can occur in masonry of any construction, are the joints where mortar holds the masonry units together.

Mortar is usually a mixture of Portland cement and sand, although a lime and sand mixture is commonly found in older buildings and is still sometimes used today.  The mason applies mortar around all adjoining surfaces of masonry units during construction and the mortar hardens to hold the masonry together.

The finished masonry wall is strong and durable once the mortar sets but the mortar joints are the wall’s Achilles heel and can become a source of seepage into the basement when they are damaged.

Although modern mortar mixes form a hard, durable material, it is still possible for mortar to deteriorate over time, especially if the mix was improperly prepared.

More likely, though, is the possibility of the mortar joints cracking and admitting water.

Foundation walls of any construction are under constant pressure and are subject to movement, sometimes in tiny increments, other times significantly.  For example, when soil surrounding the foundation becomes oversaturated due to heavy rains, snowmelt or improper yard drainage, the soil absorbs the water and expands.  This expanding soil pushes against the foundation wall and, in the case of a masonry wall, can cause masonry units to move inward.  This inward movement stresses the mortar joints and can cause them to crack.

Also, settling or sinking of a foundation can have a similar effect on mortar joints.

Any foundation is supported at the bottom by soil left undisturbed by the initial excavation.  Depending on the characteristics of the soil, the weight of the foundation and the home it supports can cause it to compress and allow the house to move downward.  This is known as “settling.”

During times of drought, trees and large plants that are located close to the foundation will extend their root systems down deeper than normal in search of water.  When these roots reach into the soil below the foundation and draw out the moisture from the soil, the soil becomes desiccated, meaning that the space between soil particles formerly occupied by water is now vacant and the soil quickly compacts to fill these voids.  The foundation it once supported will then drop to settle on the newly compacted soil, causing significant cracking in mortar joints.

Masonry Foundation Problems – Structural Damage

Some of the same factors that cause cracked mortar joints and the accompanying seepage can also cause structural damage to a masonry foundation.

Lateral Pressure – The lateral pressure against foundation walls that is created by oversaturated soil can easily cause structural damage to the foundation.

When the expanded soil pushes against the wall with enough force to crack mortar joints, it can also push the wall inward.  Typically, when this happens to masonry walls, the wall bulges or bows in the center.  In severe cases, the pressure can push masonry units out of the plane of the wall.

When this happens, the structural integrity of the wall and the entire foundation has been compromised and, left unrepaired, can cause significant damage to the home along with the intrusion of water into the basement.

Repairing this damage can range from stabilizing the wall in place to completely replacing it.

Sinking or Settling – When a foundation sinks or settles, it will cause damage throughout the home.  In minor cases, such as the settlement that often occurs in newly built homes, the damage may be limited to cracks in interior drywall and sticking windows and doors.  Worse cases may include cracking of exterior stone and brickwork and/or separation of building elements such as chimneys and additions.

When major sinking or settling occurs, entire sections of the foundation and the home it supports may drop as much as several inches, causing damage throughout the building and compromising its structural integrity. In masonry foundations, sections of foundation walls may separate at mortar joints, exposing the basement to significant seepage along with the structural damage.

Repairing significant structural damage caused by sinking or settling requires raising the foundation back to its former level and putting systems in place to stabilize it there, ensuring the long-term health of the structure.

None of these descriptions of seepage problems or structural damage is meant to imply that masonry foundations are inferior to poured concrete.  The vast majority of masonry foundations built today is constructed of concrete block, which forms a strong, stable foundation capable of successfully bearing the weight of even the largest residential structure.  Masonry has proven its value through thousands of years of use and continues to be a viable option for modern home construction, particularly where distance or other factors rule out the use of poured concrete, the most commonly used foundation material.

A homeowner who is facing seepage problems with a masonry foundation will need the advice and services of a professional basement waterproofing contractor; those with structural damage to a masonry foundation will need to call on a foundation repair expert.  At U.S Waterproofing, we have successfully repaired seepage problems in thousands of masonry basements and employ the best methods of permanent repair on either the interior or exterior of the structure.  Our foundation repair experts make use of engineering data and state-of-the-art materials and techniques to stabilize masonry foundations permanently and cost-effectively.  Why not ask for a free consultation?

Tags: masonry foundation problems, concrete block foundation problems, cinder block foundation problems

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