The Properties And Uses Of Bricks Construction Essay

Brick is a core material that is commonly used to build the wall of a building. Clay bricks are the most common brick type. It is made from sand and clay and uniformly burnt at temperatures between 800°C and 1200°C. Surface finishes are sometimes applied, e.g. glazed bricks. Glazed bricks are still being produced in large quantity and can be obtained from major English brick manufacturers and suppliers. Calcium Silicate bricks is manufactured from sand-lime (calcium silicate). The bricks are pressed under great pressure and steamed in an autoclave. The bricks are smooth, fine textured and light in colour. The colour of the brick is produced from material source, composition and firing temperature.

The size of bricks over time has changed considerably. Some early medieval bricks were 13 inches by 6 inches by 2 inches. By the late 15th century a brick 9.5 inches by 4.5 inches by 2 inches became the norm and a charter in 1571 stipulated bricks by the measurement of 9 inches by 4.5 inches by 2.25 inches. By the 18th century, 8.25 inches by 4 inches by 2.5 inches brick was introduced. Modern bricks are 8.5 inches by 4 inches by 2.5 inches which is following metrication translated to 215mm by 102.5mm by 65mm. Modern bricks are the bricks that are most used in buildings nowadays.

2.1.2 Defect of Size

Poor material selection and preparation or underfiring is the main problem of oversized bricks. Undersized bricks are caused mainly by poor material preparation, faulty moulds and overfiring.

2.1.3 Defect of Shape

There are many grounds which contribute to defects in shape. These are including poor preparation of moulds or moulding technique, faults in stacking, rough handling and uneven drying. If the bricks are considerably over burnt, incipient fusion takes place and the bricks, called burrs, will come out of the kiln or clamp and get stuck together. Burrs are suitable only for hardcore purposes.

2.1.4 Defects of Body

Faults in the raw material can give rise to defects such as cracking, bloating and laminations. Cracking and warping of bricks, causing incipient weakness, may be due to exposure of green bricks to direct sunlight or rapid drying winds. Similar effects will be produced by putting green bricks into the kiln too soon. Large cracks maybe caused by rain getting onto hot bricks.

2.1.5 Defect of Appearance

These defects are caused primarily by faulty wires in the case of wire-cut bricks. Dark spots are caused by the presence of unevenly distributed iron sulphide in the clay.

2.2 Types of Brickwork Defects

2.2.1 Introduction

Most parts of a building are built using bricks. Nowadays, brickwork defects are commonly found in buildings. This problem is getting more serious as days go by. Brickwork defects may cause a lot of problems to the occupants. The main problem encountered in building with traditional outside bearing wall of brickwork and concrete inside bearing structure is caused by differences in the temperature and moisture-induced movement. Cracks may be discovered in walls and solutions have to be found to alleviate this problem. (Verhoef, 2001)

Brickwork defect which occurs in buildings has a variety of reasons. This is perhaps not surprising when one considers the wide range of different bricks and techniques in the construction of building, differences in the construction sites and the varied occupational or owner usage of the completed building.

Brickwork will deteriorate and decay if not properly maintained. Such deterioration can be caused by a number of factors and can take various forms. The main signs that the brickwork is afflicted are surface growth and staining, efflorescence, loosed brick becoming dislodged, cracks appear through the bricks or mortar and etc. (Moses Jenkins, 2007)

In this sub chapter, the different types of the brickwork defect will be determined. This chapter gives an overview of various types of brickwork defects and understanding the brickwork defects. By identifying the different types of the brickwork defects, it will be easy for the occupants or owners to find out the causes of the defects and subsequently take the suitable remedy methods to address the problem.

2.2.2 Brick Wall Settlement

Any movement in a structural brick wall will risk having the bond courses in the wall broken. Any movement in a brick veneer wall which has broken or loosened the connections between the veneers to the underlying structure is potentially dangerous and risk collapsing the masonry.

2.2.3 Bulging Brick Wall

This is likely to be a bond-brick or bond-course failure. This defect is potentially extremely dangerous and immediate action must be taken. If not, it will cause the building to suddenly collapse.

2.2.4 Cracks and Bulges in Brick Walls

Frost and earth loading can push a below-grade brick foundation wall inwards. The wall is often bulged inwards as well as showing horizontal and step cracking and loose bricks will surface over the bulged area. The damage occurs from slightly above ground level to roughly the frost line.

2.2.5 Cracks and Loose Bricks

Normally, crack and loose bricks are caused by frost, settlement, expansion, diagonal and stair-stepped. These defects often happen at building corners where the roof spillage is concentrated.

2.2.6 Loose Bricks and Missing or Lost Mortar

This is the movement where the mortar is severely washed-out by roof spillage or other water movement against the foundation. Loose and lost bricks may also occur where wood blocks, originally set into a wall to permit nailing of interior components, is damaged by insects or decay. Similarly, if the wood joists are damaged and bent excessively or collapsed (insect damage, rot, fire), the collapsing joist can, as its in-wall end moves, damage the foundation or building wall. Fire cuts on wood joists in brick walls were intended to minimize this damage source by angling the end of the joist where it was set into the wall pocket.

2.2.7 Spalling Bricks

Spalling is caused by water and frost, such as water leaking into a brick structure at any entry point: a crack, a brick which has lost its hard surface, or at openings by window and door penetrations. It is best to also beware of caulking bricks.

2.2.8 Exfoliating-Rust Damage to Bricks

Masonry wall will have these defects when brick walls have been improperly caulked where caulking should have been omitted. The most common example of this defect is the damage that occurs to a brick wall when a steel lintel over a window or door is caulked tightly between the brick and the steel. Moisture penetrating the brick wall through cracks or mortar joints is trapped around the steel lintel. Rust developing on steel lintels has tremendous lifting power as the rusting exfoliating metal expands, sufficient to crack and damage bricks around the lintel.

Improper Repair Mortar on Brickwork

During repair works, tuck pointing or re-pointing bricks can cause surface spalling of bricks if the mason uses a too hard mortar with high portland content or mortar on soft bricks in a climate exposed to freezing weather. The high portland content means that the mortar will be not only harder, but more waterproof than the surrounding bricks. Water trapped around the hard mortar can freeze leading to surface spalling of the bricks. This is particularly likely to be seen when a wall has been tuck pointed using hard high-portland mortar where originally a soft high-lime mortar was used and where the original bricks were soft.

Salts on Brickwork

Salts are a major cause of deterioration. Salt can enter bricks through contaminated water ingress. In coastal areas, salt can come from the sea and, in winter, the nearby application of road salt is a constant threat. Salt is damaging because it creates a steady expansion of crystals within the bricks. This can eventually force the structure of the brick apart. The source of salt can occur from within the bricks themselves or from the application of contaminated mortars or renders. Brick lined chimney flues are also vulnerable as sulphates can be introduced when flu gasses condense. This is a common defect where a chimney has been sealed without adequate ventilation.

2.2.11 Efflorescence on brickwork

Efflorescence appears as a white powdery deposit on the brick. It is a phenomenon that soluble salt dissolved in water are carried, deposited and gradually accumulated on brick surfaces to form an unsightly scum. Without water, efflorescence cannot occur. The soluble salts may be originated from the raw material of bricks. But in most cases, efflorescence is caused by salts from the external sources such as ground water, contaminated atmosphere, mortar ingredients and other materials in contacts with the bricks. To minimize the risk, (it can never be completely avoided in brickwork exposed to weathering) the building detail should be designed, as far as is possible, to avoid saturation. In other words, good overhangs, copings and sills with drips, need to be considered. Efflorescence can be ‘helped on its way’ by sponging down the wall with clean water (avoiding substantial wetting) or dry brushing with soft brushes. Any other treatment should be avoided as it may disfigure the bricks. 

2.2.12 Thermal Movement on Brickwork

Every materials expand or contracts as the temperature of the material changes, typically expanding as its temperature increases and contracting as its temperature decreases. Different materials expand and contract at different rates when they undergo similar changes in their temperatures. Brick veneer can expand and contract approximately. When determining the expansion or contraction of a brick veneer, it is important to remember the effects of the sun on materials. The energy from the sun’s rays raises the temperature of a material well above the air temperature. On a day when the air temperature is 32° F, the energy from the sun can raise a wall’s temperature to above 100° F.

2.2.12.1 Thermal expansion failures in Structural or Veneer Brick Walls

A separate factor that can cause very large movements and extensive damage to brick structures or brick veneer walls is the thermal expansion which occurs across a long or tall brick wall when that wall is heated by intense sun exposure. The photographs show significant thermal expansion damage in a long brick structure.

Significant breaks and gaps at vertical brick mortar joints due to thermal expansion and perhaps some frost and water damage.

Figure1: Significant breaks in mortar

Horizontal sliding breaks in brick mortar joints, exposing reinforcing wire to rust, exfoliation, and additional damage from those forces as the exfoliating wire produced still more pressure on the mortar joint.

Figure2: Horizontal breaks in mortar

Step cracking following mortar joints near the building corners and where the wall movement was resisted by first story intersecting brick walls abutting at right angles the middle section of the long brick wall.

Figure3: Step cracking in mortar

Cracks and broken bricks at the intersections of brick walls and openings.

Figure 4: Cracks and broken bricks

(InspectApedia, 2007)

2.2.13 Moisture Movement on Brickwork

Moisture affects all porous masonry materials, including bricks, mortars and concrete masonry units but in very different ways. These effects must be considered when a combination of these materials is used, such as when bricks rest on a concrete foundation, brick veneer units are used with block back up, and when brick and architectural concrete products are used in the same Wythe bands of precast concrete or architectural concrete block in a brick veneer. After their initial mixing or casting, mortar, poured-in-place concrete and concrete masonry units shrink as the curing of the Portland cement proceeds. This is an unavoidable consequence of the curing of concrete products and is accommodated in design.

2.2.14 Sulphate Attack on Brickwork

Most ordinary clay bricks contain sulphates of sodium, magnesium or calcium. These salts are soluble in water, calcium sulphate being less soluble than the other two. Normally, these sulphates are seen as the harmless efflorescence which affect appearance only and need simply to be brushed away. In theory, most brick walls with mortars based on OPC (Ordinary Portland Cement) are liable to sulphate attack. The most vulnerable walls are earth-retaining walls and parapet walls but sulphate attack is a problem also on rendered, and facing brickwork.

On rendered brickwork, sulphate attack is manifested by cracking of the rendering, the cracks being mainly horizontal and corresponding to the mortar joints below. The rendering may adhere quite well to the bricks early in the attack but areas are likely to become detached as the expansion of the underlying brickwork causes severance of the bond between the two materials. (Eldridge, 1976)

2.2.15 Lime Staining on Brickwork

Lime staining occurs when calcium hydroxide is deposited on the face of brickwork. Lime staining will quickly absorb carbon dioxide from the air and becomes calcium carbonate. It is virtually insoluble and can only be removed by expert which is a costly treatment. The calcium hydroxide can come from three main sources:

calcium hydroxide caused by the hydration of Portland cement

from hydrated lime added to mortar

from brickwork in contact with wet concrete

2.2.16 Porosity on Brick

Porosity is an important characteristic of bricks. In contrast to other moulded or pre-cast building materials, the porosity of bricks is attributed to its fine capillaries. By virtue of the capillary effect, the rate of moisture transport in the brick is ten times faster than in other building materials. Moisture is released during day-time and re-absorbed during night-time. The ability to release and re-absorb moisture by capillary effect is one of the most useful properties of brick that helps to regulate the temperature and humidity of atmosphere in a building. This distinctive property makes bricks an admirable building material, particularly suitable for buildings in the tropics. On the other hand, all porous materials are susceptible to chemical attacks and liable to contamination from weathering agents like rain, running water and polluted air.

2.2.17 Crack in Brick Faces / Firecracks

The finished appearance of clay brick can vary greatly; this is because it is dependent on clay and the manufacturing process. Some products contain cracks of varying degree (sometimes referred to as firecracks) as an inherent feature. Firecracks are usually visible on the product as delivered. However, firecracks can be masked by the texture and surface sands used in the manufacturing process which becomes visible after the bricks are laid as a result of natural weathering of exposed brickwork.

2.2.18 Dampness of the Brick Wall

More or less permanent dampness showing more clearly on the internal wall surface from ground level up to a height of about 750mm, but may be higher in severe cases or if the outer face is covered with a non-porous finish. The decorations may be damp, blistered or discoloured, or, if dry, may have been pushed off the wall by a film or salts which will often be seen as a fluffy crystalline growth. The possible causes of dampness in the brick wall are lack of DPC (damp proof course), by-passing of the DPC, and failure of the DPC material.

2.2.19 Brick Growth and Expansion Gaps in Brickwork

Bricks undergo long-term permanent expansion over time. This expansion continues for the life of the brick, but the majority of the growth occurs early in its life. Most general purpose bricks have a coefficient of expansion in the range of 0.5-1.5mm/m (millimeters per meter) over fifteen years. Designers can use the values of the coefficient of expansion to accommodate for the growth of bricks by the size and spacing of the control joints. The provision of control gaps or articulation joints between parts of the structure during construction will accommodate movements within the structure over time. Numerous sources of movement exist and include:

The change in size of building materials with temperature, loading conditions and moisture content

The differential change in size of building materials (for example, cement products shrink over time, whilst clay bricks expand slowly over time)

Foundation and footings movement

Frame movement

Frame shortening

Temperature movement

Internal horizontal and vertical movement

2.3 Causes of the brickwork defects

2.3.1 Introduction

Brickworks are used primarily in the construction of walls. To construct the brick wall required many skills, design, experience, selection of material, and technique. Lack of all expertise may cause the brickwork defects or failure of the building. The defects that occur in brickwork maybe the result of inherent faults, deficiencies in production, design, materials or workmanship, and attack by environmental agents.

After the brickwork has been constructed, it maybe meets of various requirements, climate, loading, and occupational in use. It is not surprising that defects happened or occurs frequently.

In this sub chapter, the causes of the brickwork defects will be list out. To find out the actual causes of the brickwork defects will be easily for the occupational to take the right remedies immediately and reduces the brickwork defects happen.

2.3.2 Selection of bricks

The choice of bricks is often influenced by the price but the quality required must also be carefully considered in order to avoid defects developing during the service life of the material. Therefore, the selection of suitable bricks for any particular purpose has often to be a trade-off between appearance and durability requirements on the one hand, and cost on the other.

This is not always possible to assess the quality of bricks by the colour, variability of colour of bricks of the same source and method of production can often be an indication of strength and durability variations.

2.3.3 Storage of bricks

Bricks on site are rarely kept under adequate cover. Defects in the bricks resulting from the lack of adequate protection on the site are rarely apparent before use. However, bad weather conditions can be detrimental to bricks in that saturation by rain can be responsible for both subsequent efflorescence and decoration defects.

2.3.4 Soluble Salts in Bricks

Under burnt bricks contain a high salt content. The salts come from the raw clay from which the bricks are made, or are formed in the burning process. Most clay bricks contain some soluble salts, but the types and amounts vary appreciably. The effect of the soluble salts on both efflorescence and the more serious problem of disintegration of bricks themselves are largely governed by the strength and pores structure of the bricks.

2.3.5 Sulphate attack

Sulphates are salts which are naturally present in industrial waste, gypsum product, clay bricks, flue condensates and in some ground waters. In persistently damp conditions, sulphate will react slowly with tricalcium aluminate forming a compound called calcium sulphoaluminate. This reaction causes the cement mortar or render of the brickwork to expend and eventually disintegrate.

2.3.6 Solar Radiation

While drying out of soil by trees is the most common reason for cracking in brickwork, some clay are also very susceptible to drying out by direct solar radiation. The northern facing wall is the most likely to be affected and stepped diagonal cracking is the most common symptom, usually occurring at the north east and north west corner of the building. (Loveder, 2000)

2.3.7 Migration of moisture

The movement of moisture beneath a building can produce the phenomenon known as long term dome and saucer effect. The dome effect is a slow heaving of the soil caused by movement of moisture from the perimeter of the house to its centre, and the saucer effect is moisture moving in the opposite direction, from the centre towards the perimeter. The dome effect causes the walls to tilt outwards and the restraining influence of the roof produces horizontal cracks on the outside wall. These will be wider on the outside surface rather than the inner.

2.3.8 Planting of tree

Some of the brickwork defects may cause by big trees roots that plant nearby the building area. When planning to plant trees, the idea to be considering is the strength of the footings under the house. If lack of strength, the roots of the trees maybe grow into the ground under the building and cause the brick wall settlement and cracking.

2.3.9 Uneven settlement of foundations

Where a particular heavy load is placed on the foundation such as a large column, movement may occur as moisture is squeezed out of the soil or the soil readjusts itself. This consolidation will stop when the soil has finally compacted enough to support the load. Brick wall or masonry wall may crack which may result from movement during compaction.

2.3.10 Excessive vibration

Damage caused by vibration from earth tremors, heavy traffic or pile driving is fairly rare, however if the vibration is great enough to actually cause the foundation to move, brickwork cracking or defect can occur. The crack will show up irregularly if the sources of the vibration cannot be removed. (Loveder, 2000)

2.3.11 Additional building

Building an addition building onto a house or add more storey of houses can impose a load intensity on the soil different that which is there already and so cause differential settlement. Even if the loading intensities are similar, the difference in time between when the two settlements occurred can be enough to create the brick wall cracks.

2.3.12 Approach of design

Design of brick wall is very important. The designer must have the knowledge about the brick experience in chosen the types of brick to be used. The designer must be fully aware of the client’s needs. Defects often occur because of a lack of understanding of the different types of bricks and the method of construct the brick wall.

2.3.13 Lack experience of worker

Workers in the masonry construction is not in strict accordance with the construction and standards, masonry mortar is not full, especially in vertical mortar joints are not full, and even produce dense seam, seam permeability. In addition, the dry brick on the wall, mortar in the brick water was absorbed, causing low strength of mortar, brick and mortar separation, so that the overall stiffness of masonry fell, gray mortar joints crack.

2.3.14 Overloading

Cracks of brickwork may result from overloading of the ground on which the building rests, or of the building itself or parts of it. Releasing the load does not necessary allow the masonry wall to revert to its original state since the overloading may have been partially accommodated by a permanent compaction of the bricks. The forces responsible for the overloading may be of external origin, such as excessive wind, or may be internal, such as those arising from the installation of excessively heavy equipment for which the masonry wall was not designed. A change of occupational may have same results.

2.3.15 Lack of maintenance

Maintenance must be taken for all the building to minimize the cost of repair work for seriously defects happen. Lack of maintenance will make a small cracks or defects on brickwork change to more serious and serious.

2.3.16 Improper soil analysis and preparation

When a builder chooses an area of land to build on, it is important to do some sort of soil analysis and preparation. The analysis will provide the developer and/or builder with enough information to choose the adequate soil preparation and construction strategy that should be used to develop the land. Improper soil analysis and preparations can be very damaging to a housing development. For example, a builder can discover that the land soil is made up of expansive soil. If this is the case, houses need to have a foundation that will be able to support the changing pressure and consistency of the soil. This is because expansive soil will swell when wet and then shrink once it dries. If one builds on this type of soil and is not aware of it, there will inevitably be issues to handle. There will be crack in the brick wall or masonry wall. The repair of this is very costly and very intrusive. Unfortunately, the reality is improper soil analysis and preparations happen all the time.

2.3.17 Negligence of construction

Negligent construction is an unfortunately common occurrence. A builder has to be very careful when choosing a contractor or subcontractor. A builder will sometimes use one contactor for various projects. A contractor may have skills to install floor tiles but not the know how to build a brick wall. The responsibility can fall on several parties when there is a defect, and that’s up to your attorney to determine.

2.3.18 Movement of the ground

Mining subsidence, landslips, earthquakes, or moisture changes of shrinkable clay soil may cause the movement of the ground. The brick wall of the building will be crack because the wall of building has become displaced from the rest without any change in actual size of the materials. In theory, this is possible to reconnect the displace parts to bring the building back to its original condition but in practice this seldom can be done.

2.3.19 Acid rain

Acid rain is precipitation that is much more acidic than normal rainfall, and the acid rain is usually caused by pollution such as sulfur and nitrogen emissions. Several different mechanisms are operant in the deterioration of brick masonry through the action of acid rain. The bricks are susceptible to acid rain through the selective dissolution of their glassy phase. The mortar is affected mainly by the reaction of the calcareous components. The soluble salts resulting from these reactions, in solution with rain water or condensed moisture, will migrate through the porous matrix of the masonry. In the places where the water evaporates the salts will be deposited. Repeated dissolution and re-crystallization of these salts leads to the mechanical disruption of the masonry structure. Since the salts will concentrate in the more porous material, either the brick or the mortar will be more seriously affected, depending on their relative porosity.

2.3.20 Environment

Two aspects of the environment have been considerably which is wind and temperature. This is because they cause loading to be applied to the structure. The strong wind may cause the brick wall or the whole building move, this may cause cracking to the part of the building. The high temperature applied to the brickwork may cause spalling and brick prolong to high temperature can lead to surface vitrification. (Swoden, 1990)

Table 1: Causes of the brickwork defect and the preventive method to avoid it happen

No.

Causes of brickwork defects

Preventive method

1.

Selection of bricks

Use the bricks that are strength and durability

2

Storage of bricks

Keep the bricks under dry place

3.

Soluble Salts in Bricks

Use the bricks that are less contain of soluble salts

4.

Sulphate attack

Ensuring the wall does not get and stay in unduly wetted. Use cement low in tricalcium aluminate

5.

Solar radiation

Make sure trees plant far away from the brick wall

6.

Migration of moisture

Use of damp proof course below the brick wall

7.

Planting of tree

Make sure there have no big tree nearby the brick wall

8.

Uneven settlement of foundations

Make sure the foundation is strong enough

9.

Excessive vibration

Make sure the foundation is strong enough

10.

Additional building

Do not build additional building of brick wall after a long period finish of brick wall

11.

Approach of design

Designer must be experienced and knowledgeable

12.

Unskilled worker

Make sure the brick wall is built by skilled worker

13.

Overloading

Brick wall must be design according to building use

14.

Lack of maintenance

Must me maintenance the brickwork annually

15.

Improper soil analysis and preparation

Check the soil properly and make sure the design of brick wall is strong enough

16.

Negligence of construction

Careful when choose the contractor

17.

Movement of the ground

Make sure the foundation is strong enough

18.

Acid rain

Wash or clean the brickwork before it decay or surface treatment

19.

Environment

Use the brick that are strength and durability

2.4 Remedies method of the brickwork defects in building

2.4.1 Introduction

As known early, brickwork is one of the largest parts of most of the building. The strength, stability, and durability of brickwork are very important. If lack of all those factor, the brick wall or masonry wall maybe fall down or collapse suddenly.

If the brickwork occurs any cracking or defects, the right method of remedies must be taken immediately. This is to ensure that the occupational or owner use the building under safety and healthy purposes.

Brickwork will deteriorate and decay if not properly maintained. Such deterioration can be caused by a number of factors and can take various forms. The main signs that brickwork is suffering are surface growth and staining, efflorescence, loosed brick becoming dislodged, crack appears throw the bricks or mortar and etc. So, the right remedy must be taken to ensure the brickwork do not decay and deteriorate. (Moses Jenkins, 2007)

In this sub chapter, the remedies method for various types of defects will be list out. This is to avoid the brickwork defect getting serious in building in construction industry. The defects of brickwork must be repair immediately, if not the defects will be more serious. For example, cracking can be due to expansion or shrinkage the clay brickwork itself.

2.4.2 Remedies of efflorescence

Efflorescence can be minimized by laying dry bricks and by speeding up the drying process after the bricks have been laid by providing good ventilation. The salts that cause efflorescence are soluble in water. Hosing with water will cause the salts to dissolve and be re-absorbed into the brickwork, and then reappear when the brick wall dries out again. Acid or alkaline treatments are not recommended as they increase the salt content of the wall. The best method is simply brush off the deposit with a stiff dry bristle brush after the wall has dried out. Then sponge the surface with a damp synthetic chamois or high suction sponge. Use very little water and rinse sponge frequently in fresh water.

2.4.3 Sand-Blasted Bricks 

Which have been “cleaned” of old paint, algae, or stains using high pressure sand blasting or possibly even very high pressure water blasting can be permanently damaged by loss of the harder surface of the bricks which had been provided by their original firing. Once the softer internal brick has been exposed, the bricks will be more inclined to absorb water and to suffer water and frost damage. Sandblasting brick is considered a poor practice in building renovation and maintenance.

2.4.4 Remedies of sulphate attack

The effects of sulphate attack manifest themselves as expansion of the jointing mortar. On rendered walls the signs are horizontal cracking of the rendering with portions falling off. Advanced stages of attack may make the structure unsafe. When rebuilding is necessary, the bricks use should be of low sulphate content and the mortar should be of a mix of 1:1:6 sulphate-resistance Portland cement: hydrated lime: sand. In addition, care should be taken to exclude all conditions of dampness. On rendered walls, the rendering should be removed and the brickwork allowed to dry before reapplying a weaker mix of sulphate-resistance cement, lime and sand.

2.4.5 Tackling Decay

Where decay has occurred, take action to rectify the damage will be necessary before this leads to greater problems. The use of chemical treatments to stabilize brick should only be considered with extreme caution. Whilst the defects may be effective initially, there has been insufficient research carried out on the possible long term damage such treatments could have. Chemical sealants can trap moisture within the brick just as effectively as the claims to keep water out.

2.4.6 Cleaning

Cleaning soiled brick buildings should be undertaken carefully. In the past, the use of inappropriate cleaning techniques has resulted in considerable damage being done. If considered essential small scale tests should be employed to assess the effectiveness and likely damage which could be caused before any large scale work is carried out. There are some guides when doing the cleaning works:-

Do not re-clean brickwork with the same chemicals unless recommended by the cleaning chemical manufacturer.

If there is deterioration, or suspected deterioration, in the mortar joints, additional water and chemicals needed to remove the cleaning problem may recreate the same problem. Contact your cleaning chemical supplier for re-cleaning solutions.

Always test the remedial cleaning procedure on a small, out of the way portion of the building.

(Brick Development Association, 1986)

2.4.7 Surface treatments

Surface treatments are usually water repellents, graffiti barriers or consolidants. These should not be used on decaying brickwork. Causes of dampness should always be ascertained. Surface treatments often produce a semi sheen, and also can prevent the wall breathing and should for this reason be avoided if possible.

2.4.8 Treatment of Bulges and Fractures

In common with other types of masonry, a careful diagnosis should first be carried out prior to the repair. Fractures are usually caused by local subsidence, failure of lintels, or alterations and additions to the original structure. Bulging may similarly be the result of alterations in loadings and lack of bond between brick skins or straight joints at wall junctions. From this initial diagnosis a decision is then made to adopt one of the following measures. (Clews et al, 1997)

2.4.8.1 Leave alone

If the existing state has reached equilibrium and there is no problem affecting stability and water penetration. Sometimes more damage may be caused by cutting out or attempting to grout than by doing nothing. (Clews et al, 1997)

2.4.8.2 Cut out and re-point

Where the existing state has reached equilibrium and the cause has passed but the fractures are vulnerable to water penetration and future structural weakness. In this case the fracture should be carefully cut out with hacksaw blades, masonry saws and diamond wheels, flushed with water and pointed. If fracturing has extended through some of the bricks, these should be cut out and replaced. (Clews et al, 1997)

2.4.8.3 Stitch and Grout

The purpose of stitching is to prevent further movement taking place which would threaten the stability of the structure. Achieved with stainless steel ties, stainless steel bed joint reinforcement and reinforced concrete precast unit laid in sections as backing to facing brickwork. The method use to depend on the structure and method of failure encountered, analysis and treatment recommended by the structure engineer. (Clews et al, 1997)

2.4.8.4 Taking down and rebuild

This method may be the only solution to walls that are bulging or leaning with serious displacement around fracture. The rebuilding work should follow the original coursing, bonding and joint profile. It is a painstaking task and is undertaken only when conservation is necessary. (Clew et al, 1997)

2.4.9 Control of biological growths

Biological growths which should receive attention include unsightly algal slimes on vertical surfaces and paving, lichens causing deterioration of brickwork. The recommended method for treating masonry covered with algae, lichens, mosses and small plants is as follows:

Remove as much of the growths as possible by hand or other aids.

Prepare a solution of quaternary ammonium-based biocide according to the manufacturer’s specification, and fill a pneumatic garden type sprayer two-thirds full with the prepared solution.

Apply a flood coat, starting from the top of the vertical surface to be treated and moving across horizontally and slowly. The next horizontal pass should be made across the previous run-down.

Leave the treated area for at least one week. Brush off as much dead growth as possible, taking care to avoid adjacent gutters and hoppers.

Prepare a solution of proprietary biocide based on a quaternary ammonium compound and incorporating tributyl tin oxide or other proven durable biocide according to the manufacturer’s specification.

Fill a second pneumatic sprayer with the diluted biocide and apply in the same manner as previously described.

Allow the surface to absorb and carry out a second application of proprietary biocide as (5) above.

2.4.10 Treatment of structural damage

To treat brickwork severely damaged by causes such as fires or explosions, the following method are used:

Tie rods are fixed at the floor or roof level to anchor the suspect wall to another sound wall or structural member.

Buttresses are keyed into the suspect wall and carried to a stable base by underpinning to make sure that the buttresses actually thrust against the wall in the correct direction.

Permanent repair involves the rebuilding of the damaged wall either partially or wholly.

2.4.11 Insertion of wall ties

Insertion of wall ties is preferable to carry out the work in dry walls. If both walls are wet, assurance should be sought from the resin suppliers that the particular resin grade proposed will set properly in contact with moisture.

2.4.12 Replacement of whole bricks

Limit the amount of disruption to the adjacent sound brickwork. Replacement should match the colour, texture and size of the original bricks. Second hand bricks may be located through reclamation suppliers. Replacement facing bricks must have been exposed to weathering when previously used or could rapidly fail. Damaged, stained and previously painted bricks should be rejected. Reversing bricks is not always an option in the making good process as the brick that has failed may be inherently poor quality, for example: underfired and vulnerable to future damage. To leave bricks to darken down with natural weathering is preferable. Do not stain brickwork to overcome poor brick matching by using proprietary toners. Some camouflage staining may take a while to wash off before revealing the true incompatibility

2.4.13 Damp Proofing (Undersetting)

Older buildings tend to have a damp proof barrier (sand/asphalt) this can break down over time especially where excessive water saturation occurs. Once the barrier is breached rising damp can result. In some cases where there is dampness in winter and dryness in summer, staining or spalling to the brickwork can occur. This is a serious problem should be addressed as soon as possible undersetting can rectify the problem. This process involves the removal of defective bricks and a dpc rolled out. Completed in short stages a whole wall can be repaired without the need to rebuild completely or inject silicon.

2.4.14 Tuck-pointing

Tuck-pointing usually found in older buildings. Tuck-pointing is the placement of a white or black line on a coloured stopping (the stopping fills the mortar joint and hides any defects in the bricks). This gives the impression the bricks are of uniform size and have been laid to an accurate gauge. Modern production of bricks has superceded this process and is rarely applied today. Replacement of the joint is a time honoured skill. Incorrect mixing or application can result in early failure. Correctly done with traditional materials and the result are impressive.

2.4.15 Re-pointing mortar

To avoid irreparable brick damage, the compressive strength of the re-pointing mortar should be similar to or weaker than the compressive strength of the original mortar. Under load, a stronger re-pointing mortar will deform less than a weaker original mortar, causing the load to be concentrated on the thin strip of stronger re-pointing mortar. This stress concentration can lead to spalling of the brick face. The brick masonry is loaded by its self-weight and any externally applied loads present. In addition, the brick masonry is subjected to internal loads due to its thermal expansions and contractions and the shrinkage of the re-pointing mortar.

2.4.16 Sealant replacement

Missing or deteriorated sealants in and between brickwork and other materials such as windows, door frames and expansion joints may be a source of moisture penetration. The sealant joints in these areas should be inspected closely to discover areas where the sealant is missing, or was installed but has deteriorated, torn or lost elasticity. Deteriorated sealants should be carefully cut out and the opening cleaned of all existing sealant material. The clean joint should then be properly primed and filled with a backer rod (bond breaker tape if the joint is too small to accommodate a backer rod) and a full bead of high-quality, elastic sealant compatible with adjacent materials.