Cracks in your basement walls?  What do they mean?

Most basement walls develop at least some cracking over time.  Age and time are two of the worst enemies your foundation has.  Horizontal, vertical,  step and other cracks may mean structural issues, leaking issues, both or more – and may be costly to repair.  The seriousness of the crack usually depends on things like the size, the shape, the location and the direction of the crack.  Although not all cracks may be structural, some may indicate moisture intrusion or leakage. Cracked foundations can lead to more serious problems like framing issues, roof issues, or even issues with windows and doors not closing properly.  Following is what you need to know, and when you need to call in an expert.

Types of Basement Walls

There are four main types of basement walls, as follows.  Cracks form in each type of wall.

  • Masonry (block) walls – These walls are very common, constructed of what most people refer to as “concrete block” or “cinder block”. They are generally constructed of porous concrete with openings in the center.  Cracks can form in the actual block as well as the “grout” lines which hold the blocks together.
  • Poured concrete walls – These types of walls are gaining popularity across the country; They are generally formed by pouring concrete into metal or wooden “forms”.  Once the concrete cures and hardens, the forms are removed revealing the finished wall.
  • Precast concrete walls – These walls are built or “cast” offsite and shipped to the homesite where they are put in place by a crane.
  • Stone, brick or clay (terra cotta) tile – Popular in older homes, these walls tend to have the most cracks, leaks and faults due to their age and construction design.

Basic Causes of Basement Wall Cracks

Most of the cracks that form in basement walls are caused by one of the following:

  • Faulty backfilling when the foundation/home is built creating uneven pressures against the new wall, Often these cracks are small and cause little damage at first.  Over time they grow, creating issues.
  • Lateral loads pushing against the walls.
  • Foundation movement or “shifting” resulting from settling, soil or other issues.
  • Hydrostatic pressure involving wet and heavy soils, high “false” water tables and other water-related issues.
  • Shrinkage of the concrete in poured walls.

Most Common Types of Basement Wall Cracks

  • Horizontal cracks – Generally speaking horizontal cracks are not caused by settling issues or footer problems. They are generally created by issues that are created by lateral pressure against the basement walls.  There are several “warning” signs when looking at a block wall.  Cracks that have opened more than 1/8 of an inch in the mid-section, or where wall bowing has begun are of particular concern.  Another main area of concern is where horizontal cracks have formed within the first two or three courses of block  from the bottom, or if those blocks are beginning to shift or show other deterioration.  There are five basic causes of horizontal cracks:

 

  • Faulty backfilling – Backfilling the home right after the walls have been poured or set and/or throwing leftover building materials into the backfill field can decay, causing “open” spaces in the soil and/or decaying debris that can enter and clog French drains and other waterproofing media. Proper backfilling should occur with no more than 1/3 of the opening being filled at once and with material that allows for easy waterflow and no soil loading issues (i.e. gravel).  Over-compacting of the backfill media can also cause cracking.
  • Overloading – This occurs when the contractor allows heavy or overweight vehicles near the basement walls before they have properly cured or set, or immediately after backfilling. The weight of soil pushing against a basement foundation wall may also cause horizontal cracks, with the wall being “bowed” or “tilted” inward.  In the case of soil overloading, the greatest pressure on the wall is in the bottom third area, causing uneven pressure on the wall overall.
  • Compaction too soon or too forceful – The best way to backfill against basement walls is gradually and with a medium that does not retain water (gravel, etc.). No more than 1/3 of the depth of the wall should be backfilled at any one time, allowing for natural settling and compaction before the next level is added.  Backfilling all at once or over-compacting the backfill material is known to cause cracks.
  • Moisture loading and hydrostatic pressure – Homes with clay-based soils backfilled against their foundations will often experience cracking (sometimes severe) when that soil gets wet. These “clay type” soils tend to expand when wet, and thereby create tremendous lateral pressure against the wall.  In addition, if the soil can no longer absorb moisture, the water itself creates pressure against floors and walls, creating what is termed as “hydrostatic pressure”.  High water tables, underground springs and poor drainage are key causes for hydrostatic pressure, but there are other reasons as well, i.e. leaky sewer lines, faulty downspout or other drain lines, etc.
  • Frost heaving and/or ice lensing – Western Pennsylvania has climate conditions where the soil next to the foundation walls may experience freezing many times in a season (freeze/thaw cycles).  This freeze/thaw process exerts tremendous pressure on basement walls, so much that they can crack, tilt or bow.  Generally these cracks manifest themselves as horizontal cracks higher on the foundation walls.  Ice lensing is when pockets of moisture trapped within soil or rock freezes, creating a “localized zone” where pressure can be exerted against a portion of a foundation wall.
  • Vertical cracks – As long as vertical cracks remain straight; they are the least worrisome cracks from a structural standpoint. Cracks of this type are normally a sign of what is known as “differential settlement” (uneven horizontal and vertical pressure).  They generally occur when sections of your home settle more quickly than others or settle at uneven pressures.  Although not as serious as horizontal cracks, they are still an issue because they can allow seepage or water flow into the basement, causing further damage and deterioration.
  • Diagonal or jagged cracks – Large, jagged or diagonal cracks can indicate a structural problem and need to be reviewed by a professional.
  • Step (or stair-step) cracks – Appropriately named because they resemble a set of stairs from the side, step cracks are generally caused by uneven settling and/or shifting soil, normally under the footer. These types of cracks often indicate issues with the footer, and they are often found in the corners of foundations.  As with any type of crack, they are a problem because they indicate an unseen force working on the foundation and can also allow moisture or water to enter.
  • Cracks at basement window or door corners – Uneven pressure, causing stress is the main reason for these types of cracks, especially in poured walls. These types of cracks often develop as a result of footer-related issues or shifting of the basement wall in that immediate area.

Other Things to Know about Basement Wall Cracks

  • It is not terribly uncommon for basement walls to develop small cracks over time. Depending upon the type of crack, the severity and whether the crack is worsening is an indication of whether the crack needs to be reviewed by a professional. Moisture seepage or water flow is ALWAYS an indication that the crack needs to be reviewed by a professional.
  • Just looking at one crack or cracks in a small portion of your basement walls is not sufficient to diagnose the overall or underlying problem. The condition of all walls needs to be taken into consideration, since the foundation acts a unit, and not as independent, separate walls.
  • Many wall cracks relate to moisture issues and poor drainage. If you begin seeing cracks , or if the cracks begin seeping moisture or show water flow, you should contact a basement professional immediately.
  • Efflorescence, or a white or yellowish, chalky substance on your walls or your mortar joints is a sign that there is a moisture issue on the exterior side of the wall, which has begun translating through to the interior.

 

If you have questions about your basement foundation, or if you are experiencing  moisture or signs of moisture, like the white powder we mentioned above, contact the basement professionals at Everdry Pittsburgh for a free basement evaluation.