FOUNDATION CRACKS CAUSES AND REPAIR

Water is the main enemy. Too much water causes the soil to swell and too little may cause it to shrink. Either of these will affect the foundation adversely unless the changes in soil condition is uniform throughout the foundation. Heaving or settlement may occur as a result of this differential movement, causing cracks and damage.

• When there is an increase in soil moisture the swelling potential of expansive soils is much greater than the shrinkage potential and could be caused by plumbing leaks, subsurface water like high water table, or surface water like heavy rain.
• When there is loss of soil moisture (i.e, during drought) it causes the foundation to settle and usually near the perimeter of the foundation where the soil dries most quickly.
• Soil moisture during construction will cause the slab to hold in the moisture causing the house to settle.
• Poor pre-construction compaction of the building pad causes settlement as the supporting soil consolidates.
• Slab-on-grade foundations depend on the uppermost soil layers to support the structure and keep the foundation stable. When a structure is supported by multiple soil types the house may settle differentially causing damage to the foundation and structure.

Uniform settlement of foundation as a whole of the building causes no damage or cracks. But surrounding drainage system and underground services may get disturbed. While the differential settlement of the house is dangerous which causes cracks, damages and structural problems. With differential settlement. the foundation moves in in two directions, causing both vertical and horizontal tension. This creates horizontal, vertical and diagonal cracks in foundation.

VERTICAL FOUNDATION CRACKS

If foundation cracks are vertical, then nothing to be worry about. Even vertical foundation cracks that are slightly diagonal (within 30 degrees) but still in a straight line should be no cause for concern. Vertical foundation cracks are very common, and can be seen in ost houses. They can be occur due to concrete tension within the first few years of construction, but can also form because of heavy rains that create water pressure against the foundation wall.

DIAGONAL FOUNDATION CRACKS

Diagonal cracks usually cause more concern than vertical cracks because they indicate differential settlement that can lead to serious structural issues. When parts of a house settle more quickly than others, or sections of a home settle while other sections remain stable, it can cause differential settlement. If noticed diagonal cracks running about 30 to 75 degrees from vertical, it is important to get foundation looked at. Diagonal cracks can sometimes be hairline cracks, or widen at one end and becomes smaller at the other. Diagonal cracks often occur in some houses that are built on a hill, or houses with rapidly changing soil conditions due to heavy rain or drought.

HORIZONTAL FOUNDATION CRACKS

Horizontal cracks often indicate a more serious problem. They are caused by hydrostatic (water) pressure fro the outside of the walls and can lead to a failure of the foundation. Most foundations are designed to handle the pressure of water and soil. Additional pressure due to heavy rains or flooding can create serious horizontal cracks.

Identifying foundation problems:

Exterior indications of foundation problems

• Windows and doors do not operate properly and sometimes develop diagonal cracks at the corners.
• Cracks appear in bricks and mortar and in the exposed grade beam.
• Gaps appear at either end of wide doors and at the corner of facia trim.

Interior indications of foundation problems

• Large cracks appear in concrete slab, in the wall at the corners of doors and windows and in/around the fireplace.
• Gaps appear above cabinets and doors will not stay shut.
• Floors are uneven and existing sheetrock repairs show wear and tear.

The above indications could be caused either by settlement or upheaval. Upheaval occurs most often due to moisture under the foundation from a plumbing leak.

PROCEDURE FOR REPAIR OF CRACKS

It is advisable that individual cases, only a qualified technical engineer or an experienced contractor will be able to correctly analyse the cause and type of crack and suggest the correct suitable remedy for it. Once the cracked structure has been evaluated and the cause of cracking is established, a suitable repair procedure may be selected which takes these causes into account. The repair of concrete structures is carried out in the following two stages:

1. Pre-treatment of surface and reinforcement, i.e, removal of damaged concrete. This process is termed as the preparation of surface for repairs.
2. Application of repair material.

The following methods are generally adopted for repair of concrete and reinforcement.

Guniting (or shotcrete): A mixture of cement and sand (usually in the ratio 1:3) and water is forced or ejected through a cement gun and shot into the place by means of compressed air. The usual equipment consists of a compressor, spray machine and a flexible hose pipe. At the end of the hose, water is passed under pressure by a separate connection and is added to form a slurry. It is better if a binding coat of some materials is applied on the damaged surface before guniting. If the thickness of repaired portion is more than 25mm, expanded metal mesh can be used.

Pressure grouting (or, cement/epoxy injection): Pressure grouting, cement or epoxy grout (for thinner cracks) is injected under pressure into the cracks, voids or fissures in structures. This normally restores stability in structures which have otherwise become unstable due to cracks or void. Holes are drilled at selected points and cement grout (polyurethane or epoxy grout) which is sufficiently fluid to ensure complete penetration, is pumped in by a manually operated reciprocating pump. Holes about 40mm diameter are drilled at suitable distances apart in which nozzles are fitted.

Gravity grouting: Where possible and admissible, grouting can also be done by taking advantages of gravity. A static head is created for developing necessary pressure for grouting.

Manual patch repairs: For unimportant works, patch repairs can be done manually. Since ordinary cement-sand mortar doesn't always adhere successfully to old concrete, a polymer modified sand cement mortar should be used. Nowadays ready-made prepacked polymer modified cement mortars are available in the market. Polymer greatly increases the adhesion of the repair material to the parent concrete. It also increases the adhesion of the repair material to the parent concrete and water tightness. If there is very less thickness of repaired portion and it is structurally important, then epoxy resin mortar can be used.

Protective surface coating: If the concrete is not loose or bad quality, there are chances of chemical attack due to environmental factors, then special chemical resistant coatings can be applied on it.
While undertaking the repair of cracks in concrete may seem daunting at first, the process of fixing concrete is fairly simple. It is best to perform the repairs as soon as you see cracks appear for a variety of reasons. The primary reason to repair quickly is that the task is easier while the cracks are still small. Safety is another reason to get started right away; homeowners are responsible for any injuries that occur on their property. And lastly, cracked concrete is simply unattractive and you want to protect the looks and value of your home.

For small cracks (3 mm or less):

• Use screwdriver to chip away any flakes or loose concrete.
• Scour the crack with a wire brush to remove any dirt and debris.
• Rinse the cracked area using the garden hose.
• Mix up a small batch of concrete patching compound, available at most hardware stores. Adding a latex additive will for the natural expansion of concrete through cold and hot weather.
• Trowel the compound into the crack using a small putty knife.
• Smooth the surface while the compound is still moist; concrete compounds begin to set up very quickly.
• Allow the crack repair to dry thoroughly before walking or driving on the surface.

For large concrete cracks (6 mm or more):

While the beginning steps are the same for repairing large cracks as for small cracks, larger cracks in concrete require the use of more advanced techniques - caulking or sand packing.

• Use screwdriver to chip away any flakes or loose concrete.
• Scour the crack with a wire brush to remove any dirt and debris.
• Rinse the cracked area using the garden hose.
• If you choose to employ the caulking method, siliconized latex (or polyurethane) concrete caulk is needed. Using caulking gun, force the caulk deep into the crack along the length and breadth of the crack. The caulk will expand to fill the crack, and the nature of the substance will allow for expansion and contraction during weather extremes, cutting down on the frequency of the future repairs. The caulking compound will self-level so there is no need to smooth the surface, but for large cracks, multiple applications may be needed.
• If you choose to use the sand packing method, you will need some sand and concrete patching compound, preferably with a latex additive for flexibility. Pour in a layer of sand to help fill the crack, and then apply the patching compound with trowel. Smooth the surface quickly, and feather the new surface into the existing edges for a finished look.

FOUNDATION CRACKS CAUSES AND REPAIR

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Green Environment

Hi, I’m Gobinda Burman (Green Environment). More than 27 years in the field of Building Construction industry, I’ve completed many high-rise building projects successfully. I have got the opportunity to learn and solve the critical practical problems related to building construction. I love to share my knowledge with those people who wants to build their own home and the budding civil engineers willing to build their career in this field..

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