CRACKS IN BUILDINGS: CAUSES & REMEDIES Presented By: Er. Santosh Kumar IES (Former Sr. V.P., Reliance-ADAG) MANAGING DIRECTOR M/s VAM CONSULTING ENGINEERS.

CRACKS IN CRACKS IN BUILDINGS:BUILDINGS:CAUSES & CAUSES & REMEDIESREMEDIES

Presented By:Presented By:

Er. Santosh Kumar IESEr. Santosh Kumar IES(Former Sr. V.P., Reliance-ADAG)(Former Sr. V.P., Reliance-ADAG)

MANAGING DIRECTORMANAGING DIRECTOR M/s VAM CONSULTING ENGINEERS & ARCHITECTS M/s VAM CONSULTING ENGINEERS & ARCHITECTS

(P) LTD(P) LTD

Cracks in buildings are common Cracks in buildings are common occurrence. It develops when the stress in occurrence. It develops when the stress in a component exceeds the strength.a component exceeds the strength.

Stress is caused by either externally Stress is caused by either externally applied or internally generated force.applied or internally generated force.

External forces: Dead load, live load, wind External forces: Dead load, live load, wind load, seismic load, settlement of load, seismic load, settlement of foundationfoundation

Internal forces: Thermal moments, Internal forces: Thermal moments, moisture changes, chemical action.moisture changes, chemical action.

Classification:Classification:

Cracks are broadly classified as : Cracks are broadly classified as : Structural Structural CracksCracks or or Non Structural cracksNon Structural cracks

Structural cracks develop due to incorrect design, Structural cracks develop due to incorrect design, faulty construction or overloading.faulty construction or overloading.

They endanger the safety of the building.They endanger the safety of the building.

Non structural cracks are mostly due to internally Non structural cracks are mostly due to internally induced stresses and do not necessarily weaken induced stresses and do not necessarily weaken the structure immediately. However in due course the structure immediately. However in due course of time they allow the ingress of moisture that of time they allow the ingress of moisture that leads to corrosion of steel and thus weakening of leads to corrosion of steel and thus weakening of structure.structure.

Vertical cracks in a long building or boundary Vertical cracks in a long building or boundary wall, without expansion joint, is an example of wall, without expansion joint, is an example of non structural crack. non structural crack.

Non structural cracks do not endanger the Non structural cracks do not endanger the safety of building, but they create an safety of building, but they create an impression of faulty work or instability. impression of faulty work or instability. They also spoil the external finish of the They also spoil the external finish of the building due to penetration of moisture, building due to penetration of moisture, thus increasing the cost of maintenance.thus increasing the cost of maintenance.

Vertical cracks normally occur in walls due Vertical cracks normally occur in walls due to horizontal movement and due to to horizontal movement and due to restraint provided by the foundation.restraint provided by the foundation.

Internal stresses could be compressive, Internal stresses could be compressive, tensile or shear. Normally all materials that tensile or shear. Normally all materials that crack are weak in tension and shear, such crack are weak in tension and shear, such as masonry, concrete, plaster etc.as masonry, concrete, plaster etc.

classification of cracks based on classification of cracks based on

widthwidth..

Thin cracks : Less than 1.00 mm wideThin cracks : Less than 1.00 mm wide Medium cracks : 1 to 2 mm wide.Medium cracks : 1 to 2 mm wide. Wide cracks: More than 2 mm in width.Wide cracks: More than 2 mm in width.

Cracks may be of uniform width or varying Cracks may be of uniform width or varying width, straight, toothed, stepped, map width, straight, toothed, stepped, map pattern or random. They may be pattern or random. They may be horizontal, vertical or diagonal.horizontal, vertical or diagonal.

Cracks may be just skin deep or may Cracks may be just skin deep or may extend into the body of the material.extend into the body of the material.

Cracks need to be closely studied for correct Cracks need to be closely studied for correct diagnosis and treatment.diagnosis and treatment.

Shrinkage cracks are wider & farther apart Shrinkage cracks are wider & farther apart or thin & closely spaced. Thin cracks are or thin & closely spaced. Thin cracks are generally less damaging even if in large generally less damaging even if in large number.number.

Structures built today are more prone to Structures built today are more prone to cracks than before, due to thin section, fully cracks than before, due to thin section, fully stressed and high speed of construction. stressed and high speed of construction. Thus measures for control of cracks have Thus measures for control of cracks have assumed much greater importance assumed much greater importance

PRINCIPAL CAUSES OF CRACKSPRINCIPAL CAUSES OF CRACKS::

ii Moisture changesMoisture changes

ii.ii. Thermal variationThermal variation

iii.iii. Elastic deformationElastic deformation

iv.iv. CreepCreep

v.v. Chemical reactionChemical reaction

vi.vi. Founsation movement and settlement Founsation movement and settlement of of soilsoil

vii.vii. VegetationVegetation

Moisture Movement:Moisture Movement: Most building materials have pores Most building materials have pores

in their structure. They expand on in their structure. They expand on absorbing moisture and shrink on absorbing moisture and shrink on drying. These movements are drying. These movements are reversible and cyclic in nature. The reversible and cyclic in nature. The extent of movement depends upon extent of movement depends upon the porosity of materials.the porosity of materials.

Some irreversible movement also Some irreversible movement also takes place, e.g. shrinkage of takes place, e.g. shrinkage of cement on initial drying.cement on initial drying.

From consideration of moisture movement From consideration of moisture movement materials are classified as under:materials are classified as under:

a)a) Materials having very small moisture Materials having very small moisture movement. e.g. marble, tiles etc. movement. e.g. marble, tiles etc.

b)b) Materials having moderate moisture Materials having moderate moisture movement. e.g. bricks, concrete etc. In movement. e.g. bricks, concrete etc. In these materials some precaution is these materials some precaution is necessary.necessary.

c)c) Materials having large moisture movement, Materials having large moisture movement, e.g. timber, wood products, asbestos sheets e.g. timber, wood products, asbestos sheets

For these materials special treatment such For these materials special treatment such as protective coating of surface etc are as protective coating of surface etc are required.required.

• Irreversible shrinkage normally occurs in all building materials that are cement based. This shrinkage is one of the main causes of

cracking in structures.

• Initial shrinkage in cement concrete and mortar depends upon: cement & water content, maximum size-grading-quality of aggregates, duration-method-temperature of curing, presence of excessive fines in aggregates, humidity, type of cement, temperature of fresh concrete etc.

i. Curing is very important in minimizing initial shrinkage. If proper curing is started immediately after initial set and continued for at least 10 days, drying shrinkage is much less.

ii.ii. Presence of excessive silt, dust etc in sand Presence of excessive silt, dust etc in sand and stone aggregates has considerable effect and stone aggregates has considerable effect on shrinkage in concrete. It should not exceed on shrinkage in concrete. It should not exceed 3%.3%.

iiiiii Shrinkage is much less in coastal areas due to Shrinkage is much less in coastal areas due to high humidity whereas it is very high in plains high humidity whereas it is very high in plains of UP.of UP.

iv.iv. PPC and low grade OPC have much less PPC and low grade OPC have much less shrinkage.shrinkage.

v.v. The ideal temperature range for The ideal temperature range for concreting is 10oC to 30oC.concreting is 10oC to 30oC.

vi.vi. Sometimes cracks appear on freshly laid Sometimes cracks appear on freshly laid concrete even before it sets. This concrete even before it sets. This happens when rate of evaporation is happens when rate of evaporation is higher than bleeding. In such higher than bleeding. In such circumstances, concrete should be circumstances, concrete should be covered with plastic sheet immediately covered with plastic sheet immediately after concreting and flood cured after after concreting and flood cured after initial set has occurred.initial set has occurred.

ViiVii Cyclic changes are very prominent in Cyclic changes are very prominent in porous bricks. porous bricks. Dry bricks are water hungry and should Dry bricks are water hungry and should not be used without wetting. not be used without wetting. Brick should fully absorb water before it Brick should fully absorb water before it is laid in mortar. is laid in mortar. Also fresh bricks from kilns should not Also fresh bricks from kilns should not be used before 3-4 weeks to avoid be used before 3-4 weeks to avoid cracks in bricks.cracks in bricks.

ViiiViii Next slide shows how a small return wall Next slide shows how a small return wall cracks due to expansion.cracks due to expansion.

Measures to control shrinkage cracks:Measures to control shrinkage cracks:

In structural concrete shrinkage cracks are In structural concrete shrinkage cracks are controlled by using temperature controlled by using temperature reinforcement. Even in plain concrete a reinforcement. Even in plain concrete a minimum 0.12% steel is recommended by minimum 0.12% steel is recommended by IS: Codes. It is more effective if smaller dia IS: Codes. It is more effective if smaller dia bars- closely spaced are used bars- closely spaced are used

Cracks in masonry can be minimized by Cracks in masonry can be minimized by using rich mortar and delaying plaster work using rich mortar and delaying plaster work till masonry has dried after curing.till masonry has dried after curing.

In plaster over masonry the cracks could be In plaster over masonry the cracks could be controlled by providing good bonding with the controlled by providing good bonding with the wall. Deep raking of brick joints provide good wall. Deep raking of brick joints provide good key between the wall and the plaster.key between the wall and the plaster.

Cement plaster richer than 1:6 is harmful for Cement plaster richer than 1:6 is harmful for external wall exposed to high temperature external wall exposed to high temperature variations, since it will create a stronger variations, since it will create a stronger membrane than the surface of brick.membrane than the surface of brick.

Coarse well graded sand should be used for Coarse well graded sand should be used for plaster. Fine sand will result in crazy cracksplaster. Fine sand will result in crazy cracks ..

Strong bond between concrete and plaster Strong bond between concrete and plaster prevents shrinkage cracks, if rendering is done as prevents shrinkage cracks, if rendering is done as early as possible after removal of shuttering. Key early as possible after removal of shuttering. Key to plaster is provided by hacking and applying to plaster is provided by hacking and applying cement slurry just before rendering cement slurry just before rendering

Shrinkage cracks affect the appearance and finish Shrinkage cracks affect the appearance and finish and not the structural stability.and not the structural stability.

Cracks in walls generally get localized at weak Cracks in walls generally get localized at weak sections, such as doors and window openings or sections, such as doors and window openings or staircase walls. In external walls shrinkage cracks staircase walls. In external walls shrinkage cracks generally run downwards from window sill to the generally run downwards from window sill to the lintel of the lower storey.lintel of the lower storey.

Construction joint should be avoided in concrete. Construction joint should be avoided in concrete. However if necessary it should be located at However if necessary it should be located at one-fourth of span away from preceding beam.one-fourth of span away from preceding beam.

Shrinkage in woodwork should be concealed Shrinkage in woodwork should be concealed thro’ proper treatment of joints. Beadings often thro’ proper treatment of joints. Beadings often serve the desired purpose.serve the desired purpose.

Paint both sides of Asbestos sheets with Paint both sides of Asbestos sheets with hydrophobic colourless chemical.hydrophobic colourless chemical.

Non seasoned timber should not be used. Allow Non seasoned timber should not be used. Allow sufficient period for seasoning and reduction in sufficient period for seasoning and reduction in moisture.moisture.

Protect the surface and edges of plywood/ vaneer/ Protect the surface and edges of plywood/ vaneer/ blockboard etc with hydrophobic colourless blockboard etc with hydrophobic colourless chemical.chemical.

If rich finish is provided to external surface, If rich finish is provided to external surface, such as grit plaster, it should be done in such as grit plaster, it should be done in panels of not more than 0.50 sq.m each. by panels of not more than 0.50 sq.m each. by providing grooves of 8-10mm in both providing grooves of 8-10mm in both directions.directions.

No concreting should be done at temperatures No concreting should be done at temperatures beyond 10oC to 30oC range.beyond 10oC to 30oC range.

Under burnt bricks absorb more water, thus Under burnt bricks absorb more water, thus permitting greater moisture movement and permitting greater moisture movement and shrinkage cracks. Such bricks should be sorted shrinkage cracks. Such bricks should be sorted out and removed from the stack.out and removed from the stack.

If external finish is provided with sandstones, it If external finish is provided with sandstones, it should be coated with hydrophobic chemicals should be coated with hydrophobic chemicals that form a water repellant film. that form a water repellant film.

Acrylic or PU based chemicals are preferred. Acrylic or PU based chemicals are preferred. The film will prevent the absorption of water. The film will prevent the absorption of water.

Thermal Movement:Thermal Movement:

Thermal movement is one of the most Thermal movement is one of the most potent causes of cracking and call for potent causes of cracking and call for serious consideration. serious consideration.

It depends upon: temperature variation, It depends upon: temperature variation, dimensions, co-efficient of expansion, dimensions, co-efficient of expansion, colour, surface characteristic, thermal colour, surface characteristic, thermal conductivity, insulation, internally generated conductivity, insulation, internally generated heat etc.heat etc.

Internal walls do not suffer thermal Internal walls do not suffer thermal movement appreciably. However external movement appreciably. However external walls and roof slab, undergo severe walls and roof slab, undergo severe expansion and thus liable for cracking.expansion and thus liable for cracking.

When concreting is done in summer at When concreting is done in summer at high temperature, contraction due to drop high temperature, contraction due to drop in temperature in winter is high leading to in temperature in winter is high leading to thermal cracks.thermal cracks.

When roof in a load bearing structure undergoes When roof in a load bearing structure undergoes expansion, horizontal cracks occur in cross expansion, horizontal cracks occur in cross walls. walls.

To prevent such cracks:To prevent such cracks:

Slab should be provided thermal Slab should be provided thermal insulation.insulation.

Span of the slab should not be large.Span of the slab should not be large.

Slip joint should be provided.Slip joint should be provided.

Slab should either project beyond the Slab should either project beyond the wall or rest only partially on the wall or rest only partially on the supporting wall.supporting wall.

Plaster on inside wall and ceiling should Plaster on inside wall and ceiling should be made discontinuous by providing be made discontinuous by providing 10mm wide grove on the ceiling.10mm wide grove on the ceiling.

Formation of horizontal cracks at the support of Formation of horizontal cracks at the support of brick parapet wall over a cantilevered slab occurs brick parapet wall over a cantilevered slab occurs frequently.frequently.

There are no simple solutions to avoid such There are no simple solutions to avoid such cracks. However the following are recommended:cracks. However the following are recommended:

Construct RCC parapet instead of brick.Construct RCC parapet instead of brick.

In balconies, the supporting beam itself may be In balconies, the supporting beam itself may be inverted. Beam may be kept 150 wide to give sleek inverted. Beam may be kept 150 wide to give sleek look.look.

Defer the construction of brick parapet as much as Defer the construction of brick parapet as much as possible to allow shrinkage of supporting slab.possible to allow shrinkage of supporting slab.

Apply bonding chemical and hack the concrete Apply bonding chemical and hack the concrete surface before laying the bricks.surface before laying the bricks.

Use rich mortar in brick masonry for parapet.Use rich mortar in brick masonry for parapet.

Provide 10mm wide groove in plaster at junction of Provide 10mm wide groove in plaster at junction of brick wall and slab. brick wall and slab.

General measures for prevention of thermal cracks include General measures for prevention of thermal cracks include provision of expansion joints, slip joints, control joints etc.provision of expansion joints, slip joints, control joints etc.