You have seen a crack in your building. Now what?
Well, first it is important to understand whether it is likely to be structural or non-structural before deciding on the right course of action. While we recommend that every crack is inspected by a professional, structural cracks are far more of a concern than non-structural cracks.
Structural cracks should be addressed at once. Non-structural cracks should be monitored and taken care of, so they do not get worse.
So how do you distinguish between a structural crack and a non-structural crack?
Usually the size and location of the crack is the biggest indicator, but there are multiple things to consider. Narrow cracks (less than 1/8” wide) that have not changed over time are likely to be non-structural, while anything wider is likely to be structurally related. Below is list of causes and characteristics of non-structural cracks.
Non-Structural Cracks Characteristics
Non-structural cracks are typically very narrow from hairline width to 1/8” wide.
Non-structural cracks are commonly found at corners of doors and windows, and on plaster materials.
If a narrow crack has been present for long periods of time and are not getting any wider, then it is likely non-structural.
Non-Structural Cracks Potential Causes
Hydrostatic pressure exerted by ground water on foundations and walls due to the force of gravity.
Building settlement is the downward movement of the building caused by its load onto the ground (soil). It is common for buildings to experience some degree of settlement within the first couple of years after construction, but not too much!
Minor Shifting or Movement of Foundations.
Natural movement of groundwater and soils exert pressure on foundations causing them to move slightly.
Creep is the deformation of a material due to long term stress. This is common in wood framed building components such as floors and staircases.
Drying shrinkage occurs when moisture evaporates from a material and the volume decreases. This is especially common in concrete and plaster.
What to Do If You Notice a Crack and Think It’s Non-Structural
If you notice a crack and think it’s non-structural it is still a good idea to get a professional opinion from a qualified structural engineer. This is especially important when buying or investing money into a building as some sellers will try to cover up structural defects by painting, filling or papering over bigger cracks.
If you already own the building and don’t have money to spare for consultant fees, then you should at least monitor the crack(s). You should routinely photograph, measure and check that the crack is not getting any wider or longer or that more cracks appear. You can buy tell-tale crack monitor instruments for local hardware stores to help. Alternatively demec studs and calipers can be used to monitor crack movement.
If you notice the crack is getting wider or more cracks appear then it may be a sign that your building has more significant structural issues.
You think it’s a structural crack, but how bad is it? There are four golden questions which should be asked to determine how serious a crack may be;
- Where is it?
- What is the cause?
- How big is it?
- How bad is it?
The wider and more frequent the cracks are in the building, the more you should be concerned. Many moderate cracks can be just as worrying as one wide crack in a single location. Use the below table to help determine how severe your crack is.
Table 1 – Likely Degree of Damage with Building Cracks
|Category||Approx. Width||Degree of Damage||Description|
|0||Up to 0.01”||Negligible||Hairline cracks are classed as 0.01” or less. No action needed.|
|1||Up to 0.05”||Very Slight||Damage usually restricted to interior finishes and not visible on exterior walls. Fine cracks can be treated during redecoration.|
|2||Up to 0.2”||Slight||Crack can easily be filled or masked. May be caused by water ingress through walls. Doors and windows may need slight easing and adjusting|
|3||0.2” to 0.6”
(or several 0.1” cracks)
|Moderate||Cracks that will need opening and attention from a mason or engineer. Some external tuckpointing and possibly brick replacement may be needed. Quality of concrete and condition of steel reinforcement should be considered in concrete structures. Monitoring devices should be used at this stage.|
|4||0.6” to 1”
(but also depends on number of cracks)
|Severe||Extensive damage which needs investigation as to the cause by a structural engineer. Likely will need breaking out and replacement of damaged areas.|
|5||1” or greater||Very Severe||You need to consult with a structural engineer at once. Portions of the building may be subject to immediate collapse, injuring occpuants. Structural damage is likely to have or may be occurring which may need a major repair or rebuild project(s). Floors, beams and columns may need additional support. Foundations and walls may need shoring.|
If you notice any cracks that you cannot classify or believe may be serious, it is best to hire a structural engineer to inspect them. Any crack that rapidly widens, expands in length or changes in any other way could present serious issues. Do not try to repair these serious cracks without first speaking with a professional.
In addition to inspecting the size of the crack, the location of the crack should be considered. A crack running through a loading bearing concrete column is likely to be of a higher concern than stair step cracking through the mortar joints of a brick wall. Building materials vary in strength which should be considered when considering how much structural damage is being imposed on a building. For example, larger forces are required to crack concrete than brick as concrete has a higher compressible strength.
There are countless reasons of why structural cracks may occur within buildings such as impact damage, vegetative damage from tree roots, elastic deformation (i.e. shape deformation due to heavy building loads) and rust jacking (the corrosion of steel reinforcement within reinforced concrete which expands and pushes off (spalls) the concrete covering). However, within this article, we will discuss six common causes of building cracks.
Cause 1 – Thermal Expansion Cracks
Some building materials expand when subject to increased changes in temperatures or water content. They expand when heated in the sun or when exposed to rain or ground moisture.
This causes problems with some types of construction, especially with masonry façades. Clay brick and concrete masonry units (CMU) all have a large co-efficient of linear expansion. In other words, brick and CMU expand and grow over time when exposed to increased temperature changes and water content. This is when thermal expansion cracks may occur if preventative measures, such as control joints, are not in place.
During the manufacturing process, each brick and CMU are at their driest and smallest straight out of the kiln. As most masonry is a porous material it absorbs water from rain and the moisture within the atmosphere. This in turn increases its volume and weight causing the masonry to expand.
In simple terms, bricks and masonry units are small and dry at the start of their life but become large and wet as they age. Think of when you put a very dry sponge in bowl of water. The materials also continue to expand and contract to some extent throughout their life in the building.
As the brick masonry expands, each unit exerts pressure on the adjacent unit i.e. they push against each other. In a long masonry wall, built without expansion joints, pressure accumulates causing the wall to crack and fail. This is a common occurrence with older builds when wall construction techniques were primitive.
Expansion cracks in masonry typically form in vertical or stair-step patterns. Vertical cracks are common at corners, offsets or setbacks of brick veneer walls. Perpendicular walls will expand in the direction of the corner, causing rotation and cracks near the corner. Cracks often appear at window and door openings as well.
Thermal Expansion Crack Prevention Measures
To prevent long expanses of masonry walls from cracking and failing, building expansion joints are incorporated into the design. An expansion joint is a continuous vertical or horizontal joint, left completely free of mortar and filled with elastomeric (flexible and compressible) sealant to keep it watertight. Expansion joints accommodate this expansion as the sealant compresses.
Masonry expansion joints for brick masonry should be designed using the procedures outlined in the Brick Industry Association’s Technical Note 18A.
Generally, expansion joints within masonry walls should be provided in the following locations;
- Near corners in the masonry
- Near returns or changes in the planes of the masonry wall
- At any significant changes in the wall’s height or stiffness
- At changes in foundations and at regular intervals along the wall
- Horizontal expansion joints should usually be provided underneath the shelf angle of the overlying story in clay masonry veneers
ASTM C1472 -16 Standard Guide for Calculating Movement and Other Effects When Establishing Sealant Joint Width deals with the design principals for spacing and width of joint sealants in exterior walls and other location of buildings.
Some masonry walls may already have expansion joints incorporated but still have expansion cracks. Over time the elastomeric sealants become dry and brittle due to sun exposure, and eventually do not function as intended. If this happens the masonry is at risk of cracking due to expansion, and water ingress into the building through the damaged joints may also occur.
As a rule of thumb, the expansion joints have an estimated useful life of between 10-15 years depending on the sealant material used, climate and the quality of installation. If the sealants have failed, then the expansion joints should be replaced. This can cost anywhere between $6 to $20 per linear foot depending on width of joint and location on the building façade.
Cause 2 – Shrinkage Cracks
The opposite to thermal expansion cracks is shrinkage cracks. In this scenario cracks are caused by building materials drying out and shrinking due to a reduction in a materials’ water content. Shrinkage cracks mainly occur in concrete but can occur with any material that is installed when wet and left to cure i.e. dry out.
Concrete is a porous material which expands when wet and shrinks when dry. When concrete is mixed, more water than is needed for hydration is mixed with the dry components, such as sand, cement and an aggregate. Most of the water will eventually evaporate, causing shrinkage of the concrete slab.
After concrete is poured the concrete surface is exposed to air. This means that the surface of concrete dries and shrinks quickly due to surface evaporation and the concrete below the surface takes longer to dry and shrinks later. This differential shrinkage rate produces tensile stresses which are relieved by cracking of concrete near the surface and edges.
Shrinkage Cracks Prevention Measure
To prevent concrete from suffering shrinkage cracking, contraction joints should be incorporated into the the design. The control joints are placed in the concrete at predetermined locations to create weakened planes where concrete can crack in a straight line, below the surface.
The concrete has still cracked which is normal behavior, but the absence of random cracks at the concrete surface gives the appearance of an un-cracked section. The contraction joints can be saw cut after the concrete is poured, or can be pre-formed with a plastic or hardboard strip installing during the pouring process.
Typically, for contraction joints, the joint groove should have a minimum depth of 1/4 the thickness of the slab, but not less than 1 inch.
Cause 3 – Chemical Reactions
In some instances, harmful chemical reactions may cause cracking of concrete in buildings. These reactions may be due to materials used to make the concrete or materials that encounter the concrete after it has hardened. Such chemicals may include high amounts of alumina, chlorides or alkali-silica reaction (ASR).
Concrete may crack with time as the result of slowly developing expansive reactions between aggregate having active silica and alkalis derived from cement hydration, admixtures, or external sources (e.g., curing water, ground water, alkaline solutions stored or used in the finished structure).
The alkali-silica reaction (ASR) results in the formation of a swelling gel, which tends to draw water from other portions of the concrete. This causes local expansion and accompanying tensile stresses and may eventually result in the complete deterioration of the structure.
Alkali-silica reaction (ASR) is commonly referred to as “concrete cancer” and can often be identified by random hairline cracking and yellow/brown staining which appear to be coming from the cracks. Some ASTM Tests that screen aggregate for the potential of ASR include:
Chemical Reaction Prevention Measure
Generally, there are no treatments for ASR in affected structures. Localized repairs to damaged sections are possible, but the alkali-silica reaction will continue. In some cases, drying of the structure followed by the installation of a watertight membrane can stop the evolution of the reaction.
Cause 4 – Building Settlement
Cracks often occur because of the movement and settlement of ground soils which impact the foundations.
Building settlement is the downward movement of the building caused by its load onto the soil. It is common for buildings to experience some degree of settlement after construction, but not too much, and usually occurs within the first few years of construction. Structural cracks can occur if soils are altered after the building has settled.
The stability of soils can be affected by the weather, flooding and excavations from neighboring developments. However, the most common cause of soil movement is caused by trees, which disturb the ground by drawing up water. Even small trees can take a significant volume of water from the ground, while a large deciduous tree can need 15,000 gallons (the size of a small swimming pool) per year and in drought conditions can have an effect down to a depth of 65 feet.
When dry ground shrinks, particularly where it is largely clay, any foundation sitting on it will also move and if the shrinkage only happens under part of a building differential settlement may occur resulting in cracking as the building tries to redistribute loads.
Sometimes when a tree is removed it can add pressure onto the foundation walls. If a tree is not there to take up the water, then the ground expands and will start to push against a building and cause cracks. This is referred to as ground heave. It is basically, the hydrostatic pressure exerted by ground water on foundations and walls due to the force of gravity as shown in Figure 4. The pressure can be horizontal (from the side) or vertical (from below).
Building Settlement Prevention Measures
The best way to prevent building settlement is to ensure adequate foundation design and not alter the condition of the ground soils through the building life. However, if building settlement cracks do occur then foundation repairs me be required.
The typical repair for differential foundation settlement is underpinning piers that extend the foundation deeper into the ground to find stable soils. There are several types of underpinning repairs. The foundation pier systems offered by foundation repair contractors cost in the range of $150 to $200 per linear foot of wall to be supported for a low-rise building with shallow foundations, such as a house. This can rise exponentially if a building has basement levels and is a high-rise building.
The work is expensive and there are many variables in the soil, building construction and support methods to consider. A professional engineer can evaluate all of these factors and offer an unbiased opinion for the most permanent and efficient method of stabilization.
An independent professional engineer should inspect the property first to determine the actual cause of the differential movement and suggest any necessary repairs. If foundation repairs are suggested, the engineer can provide an engineering design plan with the proper type of pier placed in strategic locations that several contractors can use to make their bid.
Cause 5 – Poor Construction Practices
Structural cracks may occur when there is general lack of good construction practices either due to ignorance, carelessness, negligence or attempts to cut corners for cost savings. For example, building control expansion joints are sometimes not installed in long expanses of masonry walls. This is sometimes due to negligence and not specifing joints during the design phase, or the contractor purposely not installing them to reduce overall construction costs. The issue with not including expansion joints in long expanses of masonry walls is discussed above, see “Cause 1- Thermal Expansion Cracks”.
For a healthy building it is necessary that for the designer, contractor and owner to ensure the design and material selection is fit for purpose. The workmanship during construction should be undertaken with the utmost quality and care.
Poor Construction Practices Prevention Measures
Unfortunately, poor construction practices prevention can only be mitigated at design and construction stage. Choosing a reputable designer and contractor is key to ensuring the owner is left with a healthy building. Proper monitoring and use of good quality of materials is needed at the time of construction.
Cause 6 – Earthquake Damage
Structural cracks may occur due to earthquakes causing buildings to move and suddenly shift. The voids in the earth may collapse and be filled with soil from above. Many geological events can trigger earthquakes. Minor earthquakes may only cause some minor cracks here and there. Larger earthquakes may cause significant damage and threaten the safety of building occupants.
In the US, there are various maps with various levels of sophistications to show high potential seismic activity areas. For, example the below map published by the Uniform Building Code in 1997 shows that California and the west coast are at high risk of earth quakes compared to elsewhere in the US.
Earthquake Damage Prevention Measures
For new buildings, earthquake prevention should be considered at design stage by a qualified structural consultant. They will consider various seismic design factors such as site location, soil condition, torsion, dampening, ductility, building configuration, material strength and stiffness.
If you are buying, own or occupy an old building in a high seismic zone then you should consider having a seismic evaluation completed by a qualified structural engineer.
Some buyers and lenders undertake a Probable Maximum Loss (PML) evaluation to understand the seismic risk of a building. ASTM E2557 -16a Standard Practice for Probable Maximum Loss (PML) Evaluations for Earthquake Due-Diligence Assessments is the baseline standard for this process.
The seismic evaluations may suggest a seismic retrofit of some kind to make the building more resistant to earthquake damage and meet modern building code standards.
Many building codes and governmental standards influence the design and construction and renovation of buildings for seismic hazard mitigation. Codes about seismic requirements may be local, state, or regional building codes or amendments and should be researched thoroughly by the design professional.
Crack Repair Techniques
Epoxy injection is an economical method of repairing non-moving cracks in concrete walls, slabs, columns and piers as it can restore the concrete to its pre-cracked strength. The technique generally consists of setting up entry and venting ports at close intervals along the cracks, sealing the crack on exposed surfaces, and injecting the epoxy under pressure to fil the crack.
Routing and Sealing
In this method, the crack is made wider at the surface with a saw or grinder, and then the groove is filled with a flexible sealant. This is a common technique for crack treatment, and it is relatively simple in comparison to the procedures and the training needed for epoxy injection. It can be done on horizontal, vertical surfaces and curved surface.
This method is done to provide a permanent structural repairs solution for masonry repairs and cracked wall reinforcement. It is done by drilling holes on both sides of the crack, cleaning the holes and anchoring the legs of the staples in the holes with a non-shrink grout.
Drilling and Plugging
Drilling and plugging a crack consists of drilling down the length of the crack and grouting it to form a key. This technique is only applicable when cracks run in reasonable straight lines and are accessible at one end. This method is mostly used to repair vertical cracks in retaining walls.
Low viscosity monomers and resins can be used to seal cracks with surface widths of 0.001 to 0.08 in. by gravity filling. High molecular weight methacrylates, urethanes, and some low viscosity epoxies have been used successfully.
Dry packing is the hand placement of a low water content mortar followed by tamping or ramming of the mortar into place, which helps in producing intimate contact between the mortar and the existing concrete.
Monomer systems can be used for effective repair of some cracks. A monomer system is a liquid consisting of monomers which will polymerize into a solid. The most common monomer used for this purpose is methyl methacrylate.
The Brick Industry Association – https://www.gobrick.com/
ASTM C1472 – 16 Standard Guide for Calculating Movement and Other Effects When Establishing Sealant Joint Width – www.astm.org/Standards/C1472.htm
ASTM E2557- 16a Standard Practice for Probable Maximum Loss (PML) Evaluations for Earthquake Due-Diligence Assessments – https://www.astm.org/Standards/E2557.htm