Maintenance Of Non Structural Elements Construction Essay

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Non-structural elements refer to building elements which are not responsible for supporting the loading in a building. For example, non-load bearing wall (or partition), its finishing, finishing to ceiling and floor. Defects are always found in such elements during their life. In this chapter, the symptoms, causes and remedies of some common defects in non-structural members will be covered.

3.1 External Wall Appendages:

External appendages are additional attachments to the external wall, usually they are cantilevered structures which include canopies and balconies, architectural projecting features, air-conditioner supporting frame and drying racks. Although the structural designs of these elements have already ensured suitable for their cantilevered performance, poor workmanship, lack of maintenance and repair to fight against natural weathering would attract development of defects, unduly shorten their life-span and eventually result in collapse. In a worst case, such collapse might be sudden without prior obvious symptoms such as defection leading to tragic consequences.

Except for canopies which are mostly found in podium levels, other appendages are usually thin and small in size but large in numbers which are difficult to check and monitor. Therefore, adequate resources should be allocated for regular inspection and repair in order to prevent them from becoming falling hazards.

Balconies and windows of individual units usually provide good points for inspection of defects in the exterior of the building. Owners spotting any defects in the exterior of the building should report to the property manager or the Owners' Corporation (OC) for their action, irrespective of whether the defects are at the exterior of their own units or other units.

Symptoms:

Cracking at junctions

Peeling-off of painting

Loosening of attachments

Spalling concrete or uncovering(exposure) of steel reinforcement

Rusting of metal parts

Water seepage

Vegetation growth or damaged by fungus

Possible Causes:

Junction is the weak point of the structure where taking the highest loading

The appendages are exposed to weather attack

Lake of regular painting and other maintenance

Canopies and balconies are RC cantilever structures, reinforcement bars are placed near the top surface where cracks will also first start to develop. (the main reinforcements are placed near the bottom of the element in conventional reinforced concrete structures)

If waterproofing at the top is inadequate or damaged by the cracks allowing ingress of water, corrosion will reduce the effective cross-sectional area of the reinforcement bars. Then the strength of reinforcement bar for holding the cantilever slab will be lowered and cause sudden collapse.

Repair Methods:

Carry out detail investigation to check whether it is structural crack. If yes, it may be required to demolish and reconstruct, depends on the Registered Structural Engineer's (RSE's) recommendation.

Cover up the surface cracks with cement sand mortar or grouting injection

Remove the peeling-off finishes and apply with a new one

Remove the loosening of attachments, patch up or replace the corrosion parts

Repair the spalling concrete and cover up the steel reinforcement

Remove the rust of metal and repaint or replace it if necessary

Apply waterproofing material to the feature's fixing point on the external wall

Remove the vegetation or fungus, and then reinstate any damages

3.2 Advertising Signboard

Some of the advertising signboards are fixed under the soffit of the canopy and some of them are fixed on the external wall as a type of cantilever structure.

Symptoms:

Loosening of Connection

Rusting of steel

Damage on the building structures

Cause nuisance or create obstructions to the public or occupiers of the building

Dangerous to the public

Possible Causes:

Lack of maintenance

Atmospheric corrosion due to damp and pollution

Chemical corrosion

Water trapped between the laps and joints of metals

Abandoned or no longer in use

Repair Methods:

Re-fix the joints properly and carry out regular inspection and maintenance

Eliminate cause of damp conditions

Patch or replace the corroded parts and avoid contact from corrosive chemicals

Repair the damaged building structures.

Applying a protective coating to metals

Remove dangerous signboards immediately

3.3 Curtain wall

Refer to the discussion in window and partially will be further discussed in next level.

3.4 External Finishing

3.4.1 External Wall Tiling

Figure 59 - Cracking of tiling on external wall

Symptoms:

Cracking of wall surfaces

Bulging with hollow base

Loosening of parts

Falling off

Produce 'hollow sound' when tapped with a hammer

Possible Causes:

Ageing

Structural movement such as differential settlement

Thermal movement

Defective or missing expansion joints

Poor workmanship (e.g. not enough coverage of adhesive to tile, honeycomb concrete substrate etc.)

De-bonding between tile and bedding mortar(substrate directly contact the concrete), tile with bedding mortar and concrete substrate, resulting in 'hollow sound' when tapped with a hammer

Repair Methods:

If no hollow tiles found but cracking only, it can be repaired by injection of grouting or through open up and repair by retiling.

For debonding tile, all loose parts should be removed immediately to eliminate the imminent danger.

If only debonding found between the tile and the bedding mortar, remove the loose tile and re-tiling to the defective area with suitable bonding agents or adhesive in order to maintain protection to the external wall. A proper bonding of individual tile to its bedding mortar is crucial to avoid recurrence of the same defects. Adequate expansion joints should be allowed for thermal movement.

In case debonding is found between the bedding mortar and concrete wall, both tile and bedding mortar should be removed. Then apply a new bedding mortar layer to the concrete wall before retiling. A proper key between the existing concrete wall and the newly applied bedding mortar is very critical, it can be formed by applying spatterdash and slurry coat of bonding agent on top of concrete wall before laying of bedding mortar. Allow adequate expansion joints too.

When poor substrate such as honeycomb, loose concrete or spalling concrete found after removal of bedding mortar, the loose parts should be removed down to the sound concrete substrate, and then rectify the concrete defects before application of new bedding mortar. If the defects found are so extensive then replacement or addition of steel reinforcement bars, partial or demolition and recasting of certain parts of concrete elements will be considered necessary.

3.4.2 Rendering

Symptoms:

Cracking of wall surfaces

Loosening of parts

Falling off

Produce 'hollow sound' when tapped with a hammer

Possible Causes:

Ageing

Structural movement

Thermal movement

Defective workmanship

Missing expansion joints

Debonding between render and concrete substrate

Repair Methods:

If no hollow render found but cracking only, it can be repaired by injection of grouting or through open up and repair by re-rendering.

All loose parts should be removed immediately to eliminate the imminent danger.

A proper key between the existing concrete wall and the newly applied render is very crucial to avoid recurrence of such defects. The key can be formed by applying spatterdash and slurry coat of bonding agent on top of concrete wall before re-rendering.

When poor substrate such as honeycomb, loose concrete or spalling concrete found after removal of render, the loose parts should be removed down to the sound concrete substrate, then repair the concrete before application of new render. If the defects found are so extensive then replacement or addition of steel reinforcement bars, partial or demolition and recasting of certain parts of concrete elements may be required.

3.5 Paintwork on Rendering

Symptoms:

Blisters or bubbles formed

Flaking (small pieces of pant)

Peeling (larger in size)

Figure 60 - Peeling off painting on the wall

Possible Causes:

Moisture in the render had not dried out before application of painting

Chemical attack on the paint

Repair Methods:

Eliminate all sources of water or moisture affect the render

Remove the existing painting and let the render dried out

Repaint on the dry, clean and sound substrate of render

3.6 Window

3.6.1 Aluminium Window

Symptoms:

Deformed or unsecured window frames or sashes

Window sashes/hinge bars too tight to open or close

Loose or missing rivet or screw

Loose hinge bar

Greyish white powder appearing at the hinge, tracks, rivets and screw, indicating corrosion of aluminium

Water leakage between window frame and sash

Locking device of window sash not functioning properly

Broken glass pane

Missing aluminium angle for securing the glass panes

Falling off

Possible Causes:

Aging

Lack of maintenance and preventive measures

Poor design

Poor workmanship

Misuse of the window

Preventive measures:

Regularly clear the dust or dirt in the hinge bars

Keep the track and upper part of the sash dry

Lubricate the hinge bar regularly (e.g. WD40)

Should not hang any objects including clothes on the window sash to avoid causing additional load on the hinge bar

Do not impose pressure to the window sash when cleaning windows to avoid overstressing the hinge bar

Exercise caution when cleaning

Do not force to open the window

Ask for inspection and repair immediately once defects found, and inspected regularly by experienced contractors (e.g. once per 3 years)

Repair Methods:

Replace any broken or cracked glass panes at once with the same type and thickness of glass

Replacement of aluminium angle must be done at once to avoid falling of glass panes.

Replace or re-fixing the fixing components such as screw and rivets

Replace the locking device which cannot function properly to prevent damage result in typhoon

Replace the window frame at once if the window frame is deformed or unsecured. The window frame must be securely and rigidly fixed to the opening by fixing lugs. Otherwise, it will be very unstable after typhoon and may cause damage

Replace the window frame if the frame have deformed or deteriorated to a considerable extent

Replace the window frame if the quality of the frame or its waterproofing materials filling up the gap between the frame and the parent structure is in doubt, which leading to constant leakage beyond repair

Suitable waterproofing grouting should be properly applied between the window frame and the opening with an additional coat of waterproofing material around the frame

Joints in window frames and section should be properly sealed with suitable sealant. The window frame should be suitably equipped with water bars at its sill to prevent entry of water. A continuous gasket of suitable materials should also be properly applied along the whole perimeter between the window frame and openable sashes.

3.6.2 Steel Window

Figure 61 - Rusty steel window Figure 62 - Broken glass panes

Symptoms:

Rusty frames, handle or grille

Deterioration or loss of sealant to hold the glass panels

Broken glass pane

Dislodgment of sashes

Possible Causes:

Aging

Lack of maintenance and preventive measures

Repair Methods:

Repaint the frame and grille to protect the window from rusting

Regularly lubricate the hinges or replace if necessary

3.7 Internal Finishing

3.7.1 Hairline and shrinkage cracks

Symptoms:

Hairline cracks in plaster

Multi-directional cracks (shrinkage cracks)

Cracks between panel wall and structural elements such as wall or column

Figure 63 - Hairline cracks in plaster of the wall

Possible Causes:

Surface shrinkage cracks in plaster or other finishes will affect the appearance only and do not create big safety problems. Surface cracks are small hairline cracks developed within the finishing layer not penetrating down to the reinforced concrete structure.

Insufficient time for the curing of plaster

Repair Methods:

Cut and fill up the individual cracks with repair mortar and redecorate to match the existing finishes.

Resurfacing may be required if cracking is too serious.

Allow sufficient time for curing process to be completed in resurfacing

3.7.2 Differential movement cracks

Symptoms:

Cracks occur at the junction of two different materials in the background structure, e.g. concrete and brickwork

Cracks typically found in the junction between the column and wall, and the junction between the external and internal element.

Possible Causes:

Differential movement occur in the background materials such as concrete and brickwork

The background materials respond differently to the changes in humidity and temperature

Repair Methods:

Provide flexible/expansion joint by producing a groove, or filling up the gap with joint filler and sealant

Provide a cover strip which fixed to one background element only in order to cover the gap between different materials

3.7.3 Plaster Delamination

Symptoms:

Full thickness of plaster loose and come away from the background

Produce 'hollow sound' when tapped with a hammer

Cracks occur

Plaster bulges

Figure 64 - Plaster loose and falls down from the wall

Possible Causes:

Poor workmanship

Lack of good key between the concrete background and the undercoat plaster

Repair Methods:

Hack-off all of the debonded plaster from the affected area and clean the loose material

Provide a good key to the background concrete by applying spatterdash, or roughening the concrete surface. Applying a slurry coat of bonding agent on the concrete surface before re-plaster.

3.7.4 Tile Loose or Falling Off

Same as external wall tiling, refer to section 3.4.1.

3.8 Floor

3.8.1 Timber Floor

Symptoms:

Warping(distorted) of timber floor

Gaps appear between timber boards

Edges curl upwards

Possible Causes:

Gaps appearing is usually because the timber strips have not dried out adequately before being fixed, shrinkage occur leaving gaps between strips

Expansion of timber strips and insufficient expansion gaps between the strips lead to edges curl upwards

The expansion of timber strips may due to excess water used for cleaning.

Repair Methods:

Timber floor can be sanded to an overall flat surface

Replace with new timber floor if it is too serious

Sufficient gaps between the strip should be allowed for expansion

3.8.2 Plastic Floor Tiles

Symptoms:

Bulging and deterioration

Tiles are loose or edges lifted

Defects may be localized or a large area

Possible Causes:

Poor material and workmanship

The slab is not completely dried out before laying tiles

Excess water used for cleaning purpose (from above)

Repair Methods:

Find out the moisture source

Apply damp-proof membrane if necessary

Relay or replace the plastic tile with proper workmanship such as applying sufficient adhesive to the thoroughly dried slab.

3.8.3 Floor tiles

Symptoms:

Produce 'hollow sound' when tapped with a hammer

Loose / lifting of tiles

Continuous crack in tiles

Warping of tile finishes

Figure 65 - Crack and broken tiles due to insufficient expansion joints

Figure 66 - Lifting of mosaic tiles

Figure 67 - Lifting of vinyl tiles

Possible Causes:

Poor material

Poor workmanship

Insufficient expansion joint

Repair Methods:

Replacement of defective tiles

Retiling

Addition of expansion joints

3.9 Plumbing and Drainage System

3.9.1 Defective Plumbing System (fresh water supply pipe)

Symptoms

Insufficient water pressure or flows

Brownish water and deposit

Stoppage of water supply

Water leakage

Unclean water (dirt and deposit) or algae growth

Sudden rise in consumption

Noisy water pumps

Possible Causes:

Blockage or leakage of components of water supply system

Rusty of galvanized iron (G.I.) pipes or dirty supply tanks

Pump failure or breakage of supply pipe

Defective water tanks, pipe joints or valves

Defective or missing water tank cover

Leakage occur in the system after water meters

Defective water pumps, water pressure may be too high

Repair Methods:

Routine inspection and maintenance of plumbing system

Regular cleaning of water tank

Water tank should covered properly with locks

Replacement of defective pipe and its accessories including connectors and valves

Re-plumbing with copper pipe or PVC lined G.I. pipes

3.9.2 Defective Drainage System

Symptoms:

Rusty of cast iron pipes

Broken piping

Water seepage

Stinky smelt

Possible Causes:

Lack of proper maintenance such as painting

Accidental damage

Blockage of drains by rubbish collected in the system

Insufficient no. of brackets

Aging, ultra-violet (UV) attack to uPVC pipe

Figure 68 - Blockage of drains by rubbish

Repair Methods:

Regular painting of piping

Regular cleaning and removal of rubbish

Provide sufficient bracket to hold the down pipe firmly

Replacement of defective drain pipes

Replacement of the whole system

3.10 Seepage

Water seepage normally occur at underside of roofs, bottom of light wells, skylight, ceiling below bathroom, kitchen, balcony, window, external wall, basement and buried piping.

Symptoms:

Water staining

Peeling off of paint or wall paper

Water dripping

Growth of fungus

Defective concrete, plaster or tiles

Rust staining

Possible Causes:

Defective waterproofing membrane

Poor design

Failure of sealant

Hairline crack in rendering

Honeycomb of concrete

Spalling concrete

Service pipe leaked or blocked

Damage of gasket

Repair Methods:

Re-roofing or patch repair

Improve the design of floor drainage system

Reapplication sealant

Seal the crack and apply water repellant agent

Divert water to drain system

Replace defective piping

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