Bricks and Brickwork
Everything you have ever wanted to know about bricks for building
MODERN BRICKWORK AND TRADITIONAL DURABILITY
There are Buildings still standing around the world from Roman times and before that confirm that brick is a durable material
Until recent years, most buildings were built from a limited range of local bricks, employing traditional well tried methods and details. Today, modern manufacturing methods and a nationwide road and rail system make bricks from all manufacturers available everywhere.
To achieve long-term durability of brickwork in modern buildings, account must be taken of the physical properties of the bricks and mortars, as well as the degree of exposure to which parts of the building will be subjected.
Knowledge and experience of local bricks and building methods is now supplemented by the wider collective experience which has been built up over the years within the brick industry, and forms the basis of the guidance offered in this paper.
Saturation by water is the commonest potential enemy of brickwork, but recognition of this by appropriate design, specification and workmanship will ensure that modern brickwork will remain relatively maintenance free.
CAUSES OF DETERIORATION AND THEIR PREVENTION
Saturated brickwork may deteriorate for two reasons.
Firstly, saturated brickwork may be susceptible to damage by freezing when saturated. Secondly, if brickwork remains saturated for long periods, sulphate attack may disrupt the joints unless a suitable mortar is used.
Protection from saturation by design
Projecting features to shed run-off water clear of the walling below will help to prevent saturation. Roof overhangs, copings, projecting and throated sills at openings, bellmouths to renderings and other similar features may provide such protection to walls. Protection is also afforded to brickwork by damp - proof courses, and flashings, as discussed in BS 5628-3.
The frequency and extent of saturation of brickwork also depends on the degree of exposure to the weather. In areas of high exposure to driving rain, it is particularly important to give consideration to architectural features that minimise saturation and to note that elements and details in the same building may be subjected to different degrees of exposure. The NHBC guide provides information on areas of the country which are at risk of exposure to frost attack and appropriate detailing should be employed.
The presence of sulphates in soils and ground-waters can significantly affect the durability of brickwork below ground-level dpcs unless care is taken in specification. This may be particularly important in the case of earth retaining walls where correct detailing and construction are vitally important.
Vulnerable details & locations
If, for functional or aesthetic reasons, protective features are omitted, particular attention should be paid to the choice of bricks and mortar. The following are locations where brickwork is likely to remain saturated for long periods: Near ground level below dpc and in foundations. In free-standing walls, retaining walls, parapets and chimney stacks. In cappings, copings, sills, and chimney terminals.
Improper use of reclaimed/recycled bricks
Although use of reclaimed/recycled bricks is excellent from sustainability point of view it is possible for non frost resistant bricks, originally used for internal brickwork, to end up being used externally. Therefore it is recommended that reclaimed/recycled bricks be used with caution.
Further information on the use of reclaimed brick is available from the Brick Development Association and can be downloaded from their website www.brick.org.uk .
The quality of workmanship, both in the preparation of the mortar as well as in bricklaying, is a vital factor in achieving the long-term durability of brickwork. In particular full mortar bed and cross joints prevent the brickwork from retaining potentially harmful water.
The destructive effect of frost is due to the 9% increase in volume that occurs when water at 0oC is converted into ice. When bricks and mortar are saturated and frozen, expansion within the pore spaces may set up stresses that cannot be withstood. With some bricks and mortars, an open pore structure, into which the ice can expand, greatly reduces the risk of frost damage.
It is not necessarily the coldest or wettest winters that lead to frost failure, but rather recurring freeze/thaw cycles of saturated brickwork. When failure occurs, brick surfaces may flake or spall, while the mortar joints may crumble.
A manufacture must declare the frost resistance classification of its bricks and may do so based on extensive experience of their use in buildings. BS EN 772-22 ‘Methods of test for masonry units - Part 22: Determination of freeze/thaw resistance of clay masonry units’, when published, will be the only test method of assessment of freeze/thaw resistance of clay bricks.
Brickwork is particularly at risk during winter construction. As night frosts are common, even in mild winters, it is important that bricks stored on site, as well as uncompleted and new brickwork, are adequately protected from both saturation and frost. Even correctly proportioned mortar may be damaged by frost before it has fully hardened.
Uncommon and slow to develop
Examples of serious deterioration of brickwork, due to sulphate attack, such as crumbling and erosion of the mortar joint or, in severe cases, expansion, bowing and disruption of the brickwork itself, are relatively uncommon because a number of conditions have to exist simultaneously for sulphate attack to occur. Where conditions for sulphate attack are present, it may take several years before it becomes apparent.
Sulphate attack on brickwork mortars is principally caused by the reaction between sulphate in solution and the tricalcium aluminate (C3A) constituent of Portland cement, which forms calcium sulfoaluminate (ettringite). This reaction only occurs if there is an appreciable C3A content, found in OPC. The risk is greatly reduced by the use of sulphate-resisting Portland cement where the C3A content is limited to a maximum of 3.5% Sulphate attack occurs only if there is a considerable amount of water movement through the brickwork.
Diffusion alone will not carry sufficient amounts of sulphate to the hydrated cement in the mortar. Water movement may occur by percolation of water through the brickwork under the action of gravity, such as in freestanding walls or below brick sills where effective dpcs have not been provided. Movement of water may also be brought about by capillary action, for example through retaining walls that are not waterproofed on the retaining face, or in external walls between ground level and the dpc.
Sulphates from bricks
Experience shows that the use of Category S2 clay bricks reduces the risk of sulphate attack on the mortar.
Sulphates from other sources
Sulphates may come from ground-waters, from the soil, or from make-up fill adjacent to the brickwork. Where soil or ground-water sulphate levels are high, the use of strong mortar mixes containing sulphate-resisting Portland cement should be considered.
Sulphate attack can only occur when sulphate solutions can readily penetrate the mortar itself. Strong dense mortars are relatively resistant to sulphate attack, despite their higher C3A content per unit volume. The permeability of the mortar is also affected by the grading and clay content of the sand.
Parapets and free-standing walls without effective copings and dpcs, and other exposed brickwork, may remain wet long enough for sulphate attack to occur if the other conditions are present.
If dense rendering on brickwork becomes cracked, rainwater may penetrate it. Drying-out will be restricted by the render and the brickwork may remain wet long enough for severe sulphate attack and expansion to occur in the mortar joints. In all such cases, protective detailing and good specification and workmanship will minimise saturation. Additionally, the use of sulphate resisting Portland cement should be considered for the jointing mortar and the base coat of the render, particularly if category S0 clay bricks are to be used.
EXCLUSION OF WATER FROM BRICKWORK
The term, exclusion of water, is generally thought of in the context of preventing rain or ground water entering the interior of the building, however, it is equally important to minimise the amount of water entering the brickwork itself. Where this is not done, for functional or aesthetic reasons, particular care must be taken with the choice of materials.
Methods for the exclusion of water are dealt with in detail in BS 5628-3. The following factors are of particular importance, as far as the durability of materials is concerned.
Copings & Cappings - Definitions
A coping is defined as a unit or assemblage which sheds rainwater falling on it clear of all exposed faces of the walling it is designed to protect. In the case of a coping, BS 5628-3 recommends that the drip edge of the throating should be at least 40mm from the face of the wall.
Copings should be provided at the top of chimney stacks, parapet walls, free-standing walls and retaining walls in order to minimise the risk of saturation of the brickwork.
A capping, whether flush or projecting, does not incorporate a throating or similar device designed to shed water clear of the walling below.
A continuous sheet dpc should be provided beneath jointed copings and cappings, in order to prevent downward percolation of water into the wall should the joints fail. The dpc will normally be positioned immediately underneath the coping or capping. With a capping, in order to obtain greater mass above the dpc, it may be positioned one or more courses lower down. The risk of a coping or capping being displaced will be minimized by the use of a dpc designed to give a good bond with the mortar.
Ground-level damp-proof courses
Dpcs are required near the base of walls to prevent rising damp. In the case of buildings, the dpc will normally be a flexible material, although slate or brick dpcs can be used.
Brick dpcs are normally used in free-standing and retaining walls where the dpc is required to resist tension and shear. Although it is unlikely that such walls will become saturated by rising damp, the dpc does form a barrier against soluble salts from the ground and groundwater.
Damp-proof course clay bricks are classified as DPC1 and DPC2 bricks having maximum water absorption values of 4.5% and 7.0% by mass respectively. DPC1 bricks are recommended for use in buildings, while all DPC bricks are acceptable for use in external works.
They should be laid as a minimum of two bonded courses above ground level and jointed in mortar strength class M12/designation (i).
Waterproofing treatments are advisable on the soil retaining surfaces of planters and other forms of retaining wall.
Clear waterproofing treatments are not usually necessary or desirable on facing brickwork. In some circumstances, e.g. where water can enter the brickwork behind the treated surface, their use can result in deterioration since drying-out of the wall will be retarded increasing the risk of frost attack in durability designation F1 bricks.
BS 3921 has now been superseded by BS EN 771-1.
BS EN 771-1 defines clay masonry units as LD and HD units. LD units have a low gross dry density, less than or equal to 1000 kg/m3, and are for use only in protected masonry, i.e. internal walls or external wall that will not be saturated e.g. protected by impervious cladding or render.
HD units have a gross dry density, greater than 1000 kg/m3, and are for use in protected as well as unprotected masonry. Furthermore the standard defines Category I masonry units as those with a probability of failure to reach their declared compressive strength not exceeding 5%. Category II units are not intended to comply with the level of confidence of Category I units.
Many clay bricks are resistant to frost attack, while others may suffer if repeatedly frozen whilst saturated.
Resistance to frost attack cannot be reliably assessed from any of the other physical properties of the brick. Compressive strength and water absorption were once assumed to be good indicators but this is not so. In general there is no substitute for practical experience of the performance of a particular brick in service over a period of some years. BS EN 771-1 classifies bricks into three frost resistance categories F0, F1, F2, (corresponding to O, M and F in BS 3921), and are defined as follows:
F2 Severe exposure
Bricks durable even when used in situations where they will be saturated and subject to repeated freezing and thawing – equivalent to the level of frost resistance achieved by the previous “frost resistant” (F) in BS 3921.
F1 Moderate exposure
Bricks durable except in situations where they are in a saturated condition and subject to repeated freezing and thawing – equivalent to “moderately frost resistant” (M) in BS 3921.
Bricks of this category are deemed to be durable in the external face of a building provided that appropriate measures to prevent saturation have been undertaken, e.g. by provision of projecting eaves& verges, copings and sills.
F0 Passive exposure
Bricks liable to damage by freezing and thawing - equivalent to the “not frost resistant” (O) in BS 3921. Such bricks are only suitable for internal use or behind impervious cladding. During the winter they require protection from weather when stored on site or in unfinished construction.
There are three categories of soluble salt content defined in BS EN 771-14.
Category S0 bricks are not subject to any limits for specified soluble radicals and are intended for use in situations where total protection against water penetration is provided.
Category S1 bricks have limits on specified soluble salts sodium, potassium and magnesium content.
Category S2 bricks have lower limits than Category S1,bricks.
BS 3921 limited soluble salt contents to Normal (N) and Low (L).
Table NA.5 of BS EN 771-14 gives ‘BS3921 equivalent designations for all the possible combinations of categories of frost resistance and soluble salt content. BS 5628-3 prescribes the durability categories recommended for finished constructions.
Type and designation
Modern mortars made from suitable materials can be designed and mixed to provide a level of durability suitable for the brick type used and the exposure category. The types and designations of mortars specified in BS 5628-3 are given in Table 1.
In general, designation (iii), M4 mortars are likely to offer the best overall balance of properties for external walling in the UK. However, it should be noted that in conditions of severe exposure, geographically or in the building itself, designation (ii), M6 or even (i), M12 mortars may be advisable for clay brickwork.
Batching of mortar
Because the cement content of mortar is very important for it’s durability, accuracy in the proportioning of mortar mixes is essential. It is recommended that use is made of a gauge box or bucket, carefully filled without compaction and struck off level.
Where pre-mixed lime-sand mortars are used, the specified addition of cement on site should be gauged. Semi-finished factory made and pre-batched mortars should conform to the requirements of BS EN 998-2.
It should be noted that damp sand is cohesive and will normally stand up on the shovel. On the other hand, cement, being a free-flowing dry powder, will occupy a considerably smaller volume on the shovel. When the batching of mortar mixes is based on shovelfuls, the resultant mix is often considerably leaner than intended, resulting in subsequent rapid deterioration and the possible need for repointing or even rebuilding.
Importance of the materials
It is also important to ensure that the raw materials used in the preparation of the mortar are satisfactory. Normally, the raw materials should comply with the relevant British Standards. It should be remembered that Portland cement may deteriorate on prolonged exposure to the atmosphere, and therefore relatively fresh material should be used.
Excessive clay mineral content in the sand may interfere with the development of strength in the mortar. Sands with fine and relatively single-sized particle size grading may produce rather porous and permeable mortars. In either case, durability will be impaired. Sand should comply with BS 12006 in order to avoid such difficulties.
Where the brickwork is severely exposed, it may be advisable to select sand with a grading of that specified for Type S sands in BS 1200 or even for grade M sands in BS 8821.
In some areas, sands fully complying with BS 1200 in all respects may be difficult to obtain – in which case it is essential to ascertain local experience of the way alternative sands perform in use. Where unfamiliar sands are to be specified for the first time, or where there may be some doubt as to the suitability of sand from the viewpoint of mortar durability, it is recommended that trial mixes be prepared and mortar cube strength tests carried out, using the methods specified in BS 4551.
If the 28 day compressive strengths obtained meet the generally accepted minimum values quoted in various specifications (e.g. BS5628-1:2005 Table 1) satisfactory long term durability may reasonably be presumed.
Mortars at an early age are particularly vulnerable to frost damage. The use of air-entraining agents generally improves, to a limited extent, the frost resistance of mortars in newly erected brickwork, although it is important that such admixtures are used strictly in accordance with the manufacturers’ instructions regarding dosage and mixing time. However, even when air-entraining agents are used, it is still necessary to provide frost protection in winter because the mortar may still become frozen.
There appear to be no satisfactory admixtures available for use in mortars that will act as anti-freeze agents in the commonly accepted sense. Admixtures intended to provide protection by increasing the rate of liberation of the heat of hydration from the setting of the cement in the mortar are ineffective because of the small mass of cement in a given volume of masonry relative to the thermal capacity of that masonry.
Although, under threatened frost conditions, there would, in principle, be some advantage in accelerating the setting of the mortar, in practice no suitable admixtures are known that do not have other undesirable effects. In particular, calcium chloride, or admixtures based on this salt, may lead to subsequent dampness of the wall or corrosion of embedded metals, including wall ties, and should not, therefore, be used.
There is little experience of the successful use of any admixture intended to provide frost protection by depressing the freezing point of the mixing water. Some substances that might be contemplated for this purpose (e.g., ethylene glycol) are known to adversely affect the hydration of the cement.
Mortar joint profile
Bucket-handle or struck and weathered joints contribute to brickwork durability, as the tooling of the joints reduces the permeability of the mortar surface and improves the seal between the bricks and the mortar, thereby enhancing the wall’s resistance to rain penetration.
Recessed joint profiles in external brickwork will increase the level of saturation along the upper arrises of the bricks, with a consequent risk of frost damage. Such joints should only be used with frost resistant clay bricks, and the depth of the recess should take into account the proximity to the exposed face of the brickwork of perforations in the brick.
To ensure durability of the brickwork, it is essential to prevent the materials and work-in-progress from becoming saturated during construction. Bricks should be stored on a prepared hardstanding and covered with well secured polythene sheeting or tarpaulins. Cement and lime should be stored off the ground and under cover. Sand and ready-mixed lime: sand stockpiles should be placed on an impermeable base and be protected from excessive wetting or drying out, preferably by the use of polythene or similar sheeting.
Protecting new brickwork
Newly erected brickwork should be protected by covering the wall heads at the end of the working day, or during other breaks in construction, when rain is likely. Even the use of scaffold boards or flexible dpc material simply held on the wall head may provide substantial protection. Inner scaffold boards should be turned up to prevent splashing, and covers should be propped away from the brickwork so that rain is shed clear, but allowing air circulation to occur to assist drying out. When frost is likely, additional sheeting should be used to cover all freshly erected work, and dry Hessian or similar insulating material placed beneath the waterproof top covering. More detailed advice on site practice is available in the BDA booklet ‘Bricks & Brickwork on Site’
Mortar preparation & bricklaying
Accuracy in proportioning mortar mixes is important, and good supervision is necessary to ensure that mortars are not under-gauged with cement. The quality of workmanship in bricklaying may influence the life of the masonry. All joints should be properly formed.
Although bed joints are usually adequately filled, the common practice of ‘topping and tailing’ headers is to be deprecated, as it can lead to insufficiently filled perpendicular joints and an increased risk of water penetration, saturation, and deterioration of the brickwork and compromising sound insulation. All joints should be finished by tooling, when so specified, in order to improve the weather resistance of the joint.
Factory finished retarded mortars and silo mortars should be used strictly in accordance with the supplier’s/ manufacturer’s instructions.
SELECTION OF BRICKS & MORTARS FOR DURABILITY
At the design stage, the weather conditions at the time of construction will rarely be known, and indeed, building may continue through more than one winter period. The guidance notes, therefore, relate to cold weather working when night frost is expected, unless otherwise indicated.
Even so, it is essential that bricks and brickwork under construction are fully protected from saturation and freezing.
IDENTIFYING STAINS ON AND THE CLEANING OF BRICKWORK
Identification of stain or deposit and masonry materials
Before commencing any cleaning operation, it is essential to identify the type of stain or deposit and the nature of the material to be cleaned. The latter is important because there are techniques that may be perfectly satisfactory for clay products but could damage other products.
The application of inappropriate cleaning agents can create further, more permanent discolouration, which can be extremely difficult to remove.
In the case of newly built brickwork, the brick manufacturer should be consulted at an early stage. Many manufacturers have detailed experience of the cleaning of their particular products, and may be able to identify the stain and to suggest cleaning techniques that have proved satisfactory. It is important to distinguish between efflorescence and a stain. Efflorescence is soluble in water, whereas the stains considered in this note are not. It is strongly recommended therefore, that efflorescence be allowed to weather away naturally. Improvements can be seen over a short period of time, but with some products a longer period, over several seasons may be anticipated.
Cleaning should not be carried out in frosty conditions unless adequate measures are taken to protect the wet brickwork from becoming frozen.
During hot weather it is preferable that brickwork to be cleaned should be shaded from sunlight, in order to prevent the areas being treated from drying out prematurely.
Essential measures for chemical cleaning
When chemical methods of cleaning are to be undertaken, it is essential that the surface of the brickwork is first wetted. The wetting should continue until suction is reduced and the wall surface is just visibly wet.
On no occasion should a pressure hose system be used. This can lead to potential damage and may lead to an increased liability to efflorescence. An adequate supply of clean water must be available, and care must be taken to ensure that washings do not come into contact with other parts of the building. Polythene or similar sheeting may be used to collect rinsing water and convey it away to a suitable container. The chemical should not be allowed to dry out on the surface. Except where stated to the contrary, the brickwork surface should be thoroughly rinsed with water following treatment so that all trace of chemical is removed.
Cleaning small areas
Where the stained areas to be cleaned are relatively small, a suitable method is to wet down the area using a large paintbrush or spray bottle. The chemical treatment may then be applied to the stain using a paintbrush. Following the treatment, it may be necessary to scrub down the treated area with a bristle brush and water, with frequent cleaning of the brush, to ensure that the chemical is not left in the textured face of the brick.
STAINS AND DEPOSITS ON BRICKWORK
There are a number of proprietary branded cleaning agents now available, generally based on hydrochloric acid and the manufacturers’ recommendations must be followed. These are available from local trade outlets.
Cement staining from mortar and concrete
Remove large deposits with wooden implements to avoid damaging the brick face.
Following the pre-wetting of the wall, treat the residue of mortar by careful application of a 10% hydrochloric acid solution using a paintbrush. For lighter brick colours a 5% hydrochloric acid solution is preferred. The application of the acid breaks down the cementitious components but in the solutions suggested is not damaging to clay bricks.
On the rare occasions when a vanadium efflorescence is present, hydrochloric acid based cleaners must not come into contact with the efflorescence, otherwise a dark stain will result which will become fixed on the surface. If the above method is not successful with coloured mortars specialist advice from the coloured mortar supplier should be sought.
If the sand used in the mortar has appreciable clay content, the clay may enter the brick texture.
It may be possible to remove it by applying hot soapy water. A scrubbing action may be necessary, but care must be taken with sand textured bricks.
Such staining may occur on newly erected brickwork that has become saturated during construction. It may also occur under certain circumstances on established brickwork. It may come from mortar joints or from concrete and cast stone units that become saturated, and derives from free lime leaching out under excessively wet conditions. When fresh, it may be removed by scrubbing using a bristle brush and water. If left exposed to the atmosphere, lime running hardens forming a crust, known as calcium carbonate. In this condition acid treatment is likely to be required as for cement staining.
Dirt, grime, soot and smoke
Such deposits are generally the result of long term airborne deposition and as such will be difficult to remove. Scouring powder and a stiff bristle brush may be effective if the texture is not too rough. Care should be taken with sand textured products. Some alkali detergents and emulsifying agents when applied by a steam cleaner have also been effective.
If these cannot be removed by scrubbing with hot soapy water, it is likely that the techniques used by specialist cleaning contractors will be required. This may involve cosmetic tinting to restore the
Oil, grease and tar
The heavier deposits should be removed as far as possible by absorbent materials or scraping with wooden or similar implements to avoid damaging the brick face. An aerosol freeze spray can also be used for tar prior to chipping off. The surrounding brickwork should firstly be wetted to avoid the spread of contamination. The deposit or stain should also be surrounded with absorbent material. This should be followed by application of a suitable emulsifying and degreasing agent in hot water. Stubborn deposits may require scrubbing with a bristle brush. Ensure an adequate supply of absorbent material for collection of residues.
For deeper-seated stains, seek the advice of a specialist cleaning contractor.
Such growths occur naturally and impart a mellow weathered appearance to the masonry. They generally appear on brickwork which is permanently shaded from direct sunlight and which remains cold and damp for long periods of time.
Where it is necessary for such growths to be removed, the application of an algaecide will kill off the growths; these can then be removed by steam cleaning. The application of biocide will help to slow down any re-growth. Reference should be made to BRE Digests No. 370 and 418.
Paint and graffiti
Both are difficult to remove; hardened paint particularly so. Water-soluble paint removers to BS 3761(5) should be used in accordance with manufacturers’ instructions. Where the painted areas are extensive, or where the paint film is particularly stubborn, it will be necessary to seek specialist advice. When using paint removers\strippers, care must be taken to prevent the rinsing waste water from entering the drains. Paint removers\strippers are hazardous chemicals and care must be taken to ensure that all Health & Safety requirements are met.
It is essential to identify the nature of the stain as incorrect treatment can lead to problems and have an impact on other stains.
Efflorescence is a deposit of soluble minerals, which may be left on the surface of the bricks and mortar when the wall dries out. It derives naturally from clay brick and also from cementitious products or mortar. It can also be introduced as a contaminant, for example, from ground sources and from water or airborne transmission spray. White efflorescence can occur following wet working conditions, when the building dries out for the first time. Under certain conditions, it may reappear, to a lesser extent over several periods of weather cycles. It should be allowed to weather away naturally, but brushing with a non-metallic bristle brush can accelerate its removal.
Care should be taken with sand textured products. The deposit should be collected and removed so that it does not enter the brickwork at lower levels.
In some situations cleaning with an industrial vacuum cleaner has been successful. Any deposit remaining may be removed by using a clean damp sponge, which should be rinsed frequently in clean water. This will assist where efflorescence is experienced internally where natural weathering conditions will not occur. Recurrent efflorescence on older established brickwork may almost always be taken as an indication that considerable quantities of water are entering the brickwork as a result of failure of weathering and other protective measures, faulty spouts and gutters and the like.
Chemical methods should not be used for the removal of white efflorescence.
Yellow or green efflorescence
Although rare, such efflorescence can occur on new bricks, particularly on some varieties that are buff or cream in colour. They are due to the presence of vanadium salts, a transitional metal compound and a naturally occurring ingredient of some clay. If brickwork exhibiting such efflorescence is washed with inorganic or proprietary hydrochloric acid based brick cleaning solutions, a dark coloured stain, which is permanent, is frequently produced, hence this efflorescence should be allowed to weather away naturally.
If this efflorescence is so pronounced as to necessitate chemical methods of removal, the following methods have been used, but it is strongly recommended that initial trials be carried out on small areas of brickwork. Brush on sodium hypochlorite or household bleach in concentrated solution, and, when bleached, apply washing soda solution (12g/litre) and leave on the wall. For more persistent stains, brush on oxalic acid solution (100g/litre), and, when the stain is bleached, apply washing soda solution (12g/litre) and leave on the wall.
Remember not to clean other stains whilst vanadium salts are visible.
This can appear in several forms from orange through to dark brown in colour and can affect both the brick face and lead to surface staining of the mortar joint. Where in severe cases it is present on the brick face, it is best left to weather away naturally. Iron staining will recede over time but the following techniques have found to be successful in removal of the stain. Removal from the face of the mortar joint is best achieved by scraping or rubbing with a round file or carborundum slip. Where overall cleaning is required, the following chemical treatment has been found to be successful. Brush on 5%-10% hydrochloric acid solution. This is frequently satisfactory on fresh stains. To this end, proprietary brick cleaners may be effective, but, as with all treatments, a small trial area should be carried out first. For more persistent stains, repeated application may be necessary.
This is similar to iron staining but is generally dark brown or black in colour, and the treatment is similar. If chemical treatment is required the following methods have been used. On fresh stains, brush on 5%-10% hydrochloric acid solution or a proprietary brick cleaner In more severe cases a combined solution of hydrochloric acid (10%) and hydrogen peroxide (10%) can be effective or, alternatively, paint the stain with oxalic acid solution (100-120g/litre).
Staining of Blue Bricks
Staining of blue bricks is commonly called ‘Peacocking’. It appears as an oil coloured type of stain on the face of the bricks and is a natural characteristic of these products.
The most common stain to blue bricks, similar in appearance to ‘Peacocking’, is associated with the saturation of bricks and brickwork prior to and during construction which leads to calcium deposits drying on the face of the bricks. Good site protection to unused bricks and incomplete brickwork is essential to minimise, and in many cases, prevent this stain occurring.
Baggeridge Brick plc
Tel: 01902 880555