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Defects in buildings & remedies


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Defects in buildings & remedies

  1. 1. DEFECTS IN BUILDING: Building defect is one of the major components of building problems that significantly needed attention. When a building fails to function as it should, we must immediately seek for the determination. Building defect occurs to either the new building or the old ones. Defect within new buildings is maybe of non- compliance with Building Code and published acceptable tolerances and standards. Meanwhile the older buildings, or building out of warranty period, may not comply with these standards but must be judged against the standard at the time of construction or refurbishment. Defects and deterioration are common problems in any built structures. However, various defects are more common in an old structure. Defects are defined as the deterioration of building features and services to unsatisfactory quality levels of requirement of the users. CATEGORY OF BUILDING DEFECTS : The defect can be divided into two categories, which are: A) STRUCTURAL DEFECT Structural defect means any defect in a structural element of a building that is attributable to defective design, defective or faulty workmanship or defective material and sometimes any combination of these. Building structure includes earth retaining walls, columns, beams and flat slabs. According to the Engineering Encyclopedia, structural defect can be categorized as cracks in foundations (Substructure), cracks in floor or slabs (superstructure), and cracks in walls (superstructure). These defects can be caused by improper soil analysis, inappropriate site selection, and the use of defective materials. Most of the structural problem can be avoided by implying the exact and detail of the design and planning. Structural defects in a building can occur over time due to deterioration, wear and tear, overloading, and poor maintenance. They must be repaired to maintain the building’s structure and to prevent any further failures. Regular inspection is the key to protecting the ‘health’ of a building’s structure. Structural defect that always occurs are steel corrosion, cracks, and deflection. B) NON-STRUCTURAL DEFECT A non-structural defect in a residential building is described as a defect in a non-structural element of the building as a result of defective residential building work. According to the Engineering Encyclopedia, non-structural defect includes defect in brick work, dampness in old structures, and defects in plaster works. COMMON BUILDING DEFECTS: In general, there have several building defects which usually occur to building parts such as roofs, walls, floors, ceiling, toilets, doors and windows. Building difficulty and defect that are regularly found will be discussed in the following section which consists of wall crack, peeling paint, dampness, timber decay, fungi and small plant attack, sagging or deformation, erosion of mortar joint, defective plaster rendering, insect or termite attack, roof defect, and also unstable foundation, and services.
  2. 2. CRACK ON WALLS It is the nature of many construction materials to crack as they age and as they expand and contract, particularly with exposure to moisture as they get wet and dry out alternately. There are cracks in common areas, such as exterior walls, interior walls at corners of doors and windows, and ceilings (usually in the middle). Crack defect have classified of visible damage to walls. There is having different state in category of damage, and degree of damage. According to the construction, the occurrence of wall crack is because they are overloaded or because the structure has settled or heaved. Vertical and angled crack are usually caused by settlement or heaving. Nevertheless, for horizontal crack are more likely to be caused by lateral pressure.
  3. 3. There are varieties types of vertical crack such as: A) VERTICAL CRACK AWAY FROM CORNERS The crack is running along between the foundation and the top of the building. Cracks are usually the widest at the top of the building diminishing to a hairline crack at or near the foundation level. They may run through the foundation or they may only start above first floor opening. It is obviously detected in each of the opposite elevations of the building, will be a single crack, and may be connected by a crack in a concrete floor or a flat roof. Besides that, the roof finishes of the pitched roof may be stretched or pulled apart. Diagonal cracks may also be associated with the defect. B) AT THE CENTRE OF PANEL Cracks occur near to centre of a panel of cavity brickwork, The crack is the widest at the bottom and may narrow to a hairline crack at the top (especially where the brickwork does not reach the top of the panel). The phenomenon usually occurs where panels of brickwork are set between columns, especially if they are of in-situ reinforced concrete.
  4. 4. C) BETWEEN BAY WINDOW CORNERS Cracking at sides of bay windows, In either is the masonry or timber stud construction. It may become quite wide ranging in 5 – 15mm. CRACKS CAN BE DIVIDED INTO TWO TYPES: A) STRUCTURAL CRACKS: These cracks occur due to incorrect design, faulty construction or overloading and these may endanger the safety of a building.
  5. 5. B) NON-STRUCTURAL CRACKS: They are due to internal forces developed in materials due to moisture variations, temperature variation, crazing, effects of gases, liquids etc. Non-Structural Cracks are:  Plastic Settlement  Plastic Shrinkage  Early Thermal Expansion and Contraction  Long Term Drying Shrinkage  Crazing  Due to corrosion of concrete  Due to Alkali-Aggregate Reaction  Sulphate Attack  Due to corrosion of Steel CAUSES & ITS PREVENTIVE MEASURES : A. ELASTIC DEFORMATION It occurs when a material strains under stress. When two materials (having different elastic properties) built together under the effect of load then different shear stresses in these materials create cracks at the junction. Dead and live loads are the main cause of elastic deformation in any structural components of a building. Preventive Measures: Create slip joints under the support of concrete slab on walls. Provide horizontal movement joints between the top of brick panel and reinforced cement concrete beam/slab. B. THERMAL MOVEMENT Most materials expand when they are heated, and contract when they are cooled. The expansion and contraction with changes in temperature occur regardless of the structure’s cross-sectional area. It is one of the most potent causes of cracking in buildings which need attention. Preventive Measures: Joints should be constructed like construction joints, expansion joints, control joints and slip joints. The joints should be planned at the time of design and be constructed carefully.
  6. 6. C. CHEMICAL REACTION Chemical reactions may occur due to the materials used to make the concrete or materials that come into contact with the concrete after it has hardened. Concrete may crack with time as the result of slowly developing expansive reactions between aggregate containing active silica and alkalis derived from cement hydration, admixtures or external sources. Preventive Measures: If sulphate content in soil exceeds 0.2 percent or in ground water exceed 300 ppm, use very dense concrete and either increase richness of mix to 1:1/5:3 and to prevent cracking due to corrosion in reinforcement it is desirable to specify concrete of richer mix for thin sections in exposed locations. D. SHRINKAGE Most of the building materials expand when they absorb moisture from atmosphere and shrink when they are dry. Shrinkage can be of plastic or dry. The factors causing shrinkage in cement concrete and cement mortar and their preventions are as following. 1) Excessive Water: The quantity of water used in the mortar mix can cause shrinkage. Vibrated concrete has less quantity of water and lesser shrinkage than manually compacted concrete. Preventive Measures: Use minimum quantity of water required for mixing cement concrete or cements mortar according to water cement ratio. Cement concrete is never allowed to work without mechanical mix and vibrator. 2) Quantity of Cement: As a general rule, the richer the mix is, the greater the shrinkage/drying will be. Preventive Measures: Do not use excessive cement in the mortar mix. E. FOUNDATION MOVEMENT AND SETTLEMENT OF SOIL Shear cracks in buildings occur when there is large differential settlement of foundation and it may be either due to the following reasons:  Unequal bearing pressure under different parts of the structure  Bearing pressure on soil being in excess of safe bearing strength of the soil  Low factor of safety in the design of foundation Preventative Measure: The design of foundation should be based on sound engineering principles and good practice.
  7. 7. F. EARTHQUAKE Crack may occur due to sudden shift in lower layer of the earth. The voids in the earth might have suddenly collapsed and be filled with soil from the above. Many geological events can trigger earth movements but is continuous movement. Preventive Measures: Construct the foundation of buildings on firm ground while doing construction. Tie up the building with connecting beams at foundation level, door level and roof level. G. VEGETATION Fast growing trees in the area around the walls can sometimes cause cracks in walls due to expansive action of roots growing under the foundation. The cracks occur in clay soil due to moisture contained by roots. Preventive Measure: Do not grow trees too close to the building. Remove any saplings of trees as soon as possible if they start growing in or near of walls. H. POOR CONSTRUCTION PRACTICES There is a general lack of good construction practices either due to ignorance, carelessness, greed or negligence. For a healthy building it is absolutely necessary for the construction agency and the owner to ensure good quality materials selection and good construction practices. Preventive Measure: Proper monitoring and use of good quality of materials is required at the time of construction TECHNIQUES TO CURE CRACK : A. EPOXY INJECTION Epoxy injection is an economical method of repairing non-moving cracks in concrete walls, slabs, columns and piers as it is capable of restoring the concrete to its pre-cracked strength. The technique generally consists of establishing entry and venting ports at close intervals along the cracks, sealing the crack on exposed surfaces, and injecting the epoxy under pressure.
  8. 8. B. 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 required for epoxy injection. It can be done on vertical surfaces and curved surface C. STITCHING 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. D. DRILLING AND PLUGGING 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. E. GRAVITY FILLING 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. F. DRY PACKING It is the hand placement of a low water content mortar followed by tamping or ramming of the mortar into place and also helps in producing intimate contact between the mortar and the existing concrete. G. POLYMER IMPREGNATION 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. DAMPNESS: Dampness is generally defined as unwanted and excessive water or moisture. The existing of dampness in building is one of the most damaging failures that really must be taken care of. It can cause damage in brickwork by saturating them, decaying and breaking up of mortar joints, rotting in the timber structures, defecting by the corrosion of iron and steel materials and also destroying the equipment in the building. Dampness in walls has been taken in consideration in recent years. If even the level of dampness is low, the value of the building can be highly affected.
  9. 9. THE THREE MOST COMMON SIGNS ARE: 1. SURFACE STAINS Water moving through bricks, blocks etc may dissolve some of the alkaline salts from the mortar. The salts can then react with the tannins in timber, wallpaper or the like to produce stains that are usually brown. The stains can be unsightly, but do not cause damage. Some clay bricks with vanadium salts stain brown or purple after being cleaned with spirits of salts (Le. hydrochloric acid, which is often applied to remove mortar splashes). Such stains usually disappear with a scrubbed-on application of diluted caustic soda (eg. some dishwashing detergents) but the stains can sometimes be stubborn and will then require specialised treatment. 2. LIFTED SURFACE FINISHES As a wall affected by damp dries, the water will be drawn to the surface and find itself trapped under the paint film or other surface finish. The evaporating water lifts the film in bubbles that will eventually break to leave blisters. Wallpaper or other applied finishes, including timber panels, can be similarly damaged. 3. EFFLORESCENCE AND FRETTING Where there is a continuous supply of water rising up a wall, it will contain dissolved salts, and when that water dries out at the surface, the salts will crystallise. If the crystals form on the surface of the wall as a white furry coating, it will be suffering from non-damaging efflorescence, but if the crystallisation occurs within the bricks or mortar, the forming crystals can exert pressure that causes the surface to break down and fret away. With rising damp, there is generally a continuous supply of water (such as damp soils around and under the footings and walls) so salt attack damage worsens.over time, but it usually reaches a stage where crystallisation occurs only on the surface as efflorescence and fretting stops. CAUSES OF RISING DAMP OR "SALT-DAMP" : Dampness can be a serious matter, particularly to the building located near water sources. Somehow, the water can enter the building bit by bit through different routes resulting in dampness. Furthermore, prevailing wet wind and rain will due to water penetrations that occur through walls. Dampness also occur when water penetrate through capillaries or cracks between mortar joints, and bricks or blocks before building up trap moisture behind hard renders. Moreover, contribution of dampness is due to the existence of gravity. The other factor such as leaking gutters or down pipes, defective drains, burst plumbing, and condensation due to inadequate ventilation also can be the factors yielding to dampness occurrence. DAMPNESS IN BUILDING ORIGINATED FROM A NUMBER OF SOURCES SUCH AS: A) RAIN Precipitation can be wind driven that it penetrates joints that remain watertight in normal weather condition. The gutter overflow also can collect and be the aspects of dampness against walls.
  10. 10. B) CONDENSATION Humid air condensation on cooler surface or within, or between, building materials also can result to dampness. Air can become humid in several ways, including from the occupants’ water vapours. C) RISING DAMP AND FLOODING It may be contract with groundwater or floodwater. It also the groundwater may be absorbed by the walls and transported up the wall by capillary action. D) SERVICES LEAKS It may not just from pipes and tanks, but also the overflowing of condensation forming together with ventilation systems. E) CONSTRUCTION PROCESS The construction process too can play its role in this scenario. It is where the process of mixing water to form mixtures that dry out for the construction purpose before the building is functioned, but sometimes by retaining moisture (sealed in by impermeable finishes) that shows and causes problems in the completed building. F) USE OF THE BUILDING This may includes the cleaning of the building, spills, and apparatus leaking. G) MOISTURE IN THE AIR It is in contrast with condensation. Hygroscopic salts can extract moisture from the air in condition that would not allow that moisture to undergo the process of condensation. Dampness comes and goes according with the change of condition. Dampness also may leave stains or traces of mould and lichens and also in certain cases, mosses. METHODS TO PREVENT DAMPNESS IN BUILDING AT THE TIME OF CONSTRUCTION: The following are the precautions to be taken to prevent dampness in buildings, before applying the various techniques. 1. The site should be located on high ground and well-drained soil to safe guard against foundation dampness 2. All the exposed walls should be of sufficient thickness to safeguard against rain protection (minimum 30 cm) 3. Bricks of superior quality free from defects should be used 4. Good quality cement mortar (1:3) should be used to produce definite pattern and perfect bond in the building 5. Cornices and string courses should be provided to repel rain water away from the walls 6. All the exposed surfaces like top of walls, compound walls etc. should be covered with water proofing cement plaster 7. Cavity walls are more reliable than solid walls in preventing the dampness
  11. 11. TECHNIQUES: 1. Use of damp proof courses 2. Water proof or damp proof treatments 3. Integral damp proofing treatment 4. Cavity walls or hallow walls 5. Guniting or shot concrete or shotcrete 6. Pressure grouting or cementation CURES FOR RISING DAMPNESS: REPAIR THE DAMAGED DAMP-PROOF COURSE: A deteriorated damp-proof course is nearly always one that has cracked rather than physically broken down. The associated damage is usually local and close to the crack. In the case of isolated patches of rising damp due to this cause, local insertion of a new damp-proof course followed by treatment of deteriorated plaster or other wall covering will usually be appropriate. IMPROVE SUB-FLOOR VENTILATION Rising damp can often result from a lack of sufficient, partly or completely blocked, sub-floor ventilators or vents. Typically, older brick dwellings have an inadequate number of sub-floor vents. Blocked ventilators commonly occur where the ground or garden bed level around the house has risen over time, or a new path or verandah paving has been laid at a higher level than the ventilators. Removing the obstruction or lowering the ground or garden bed level will frequently fix the problem. Where this is not possible, ducts connected to sub-floor vents that rise above the obstruction, will frequently bring the desired cure. REPAIR LEAKING PLUMBING Modern domestic water meters measure the volume of water passing through them with such accuracy that they can be used to test for leaks. If all the taps are turned off and the meter still registers a flow of water, there must be a leak. Cracked or damaged waste pipes - sewer or stormwater - should also be investigated preferably by a licensed plumber. These may be more problematic to detect. Repair of leaking water pipes or drains will eliminate them as a cause of the problem and should be undertaken by a licensed plumber. Remedying the damage caused will often require additional effort.
  12. 12. INSTALLING NEW DAMP-PROOF COURSE Where the remedies described above are ineffective or not possible it will be necessary to embark on the process of inserting a new damp-proof course. There are a variety of methods of doing this, but two dominate: 1. PHYSICALLY INSERT A NEW MEMBRANE A mortar bed-course, at a level below the lowest floor frame member is cut out and a new damp-proof course membrane is then inserted into the resulting horizontal gap. The main difficulty is in ensuring that the mortar caulking around the new membrane is adequate to support the wall above. Because of this problem, the technique is now mostly associated with a patented method using a plastic bag as the membrane. It is inserted into the joint and then pumped full of a quicksetting mortar to ensure support. 2. CREATE A CHEMICAL DAMP-PROOF COURSE A horizontal row of holes is drilled into the bricks or mortar and they are then injected with a chemical - usually polysiloxane -under the pressure of gravity or using a pump to impregnate a band of bricks and mortar that render that layer of bricks highly resistant to the passage of water. This method has the great advantage that it does not interfere with the structure, but like all other methods of damp proof insertion, its effectiveness is highly reliant on the care taken and the expertise of an experienced tradesperson.