5. Cleaning and Ancillary Repair Works

 

5.1 Cleaning

5.1.1 General Considerations

5.1.2 Buildings of Architectural or Historic Interest

5.1.3 Choice of Method

5.1.4 Materials to be Cleaned

5.1.5 Deposits to be Removed

5.1.6 Cleaning Methods

5.2 Treatment of Walls with ‘Waterproofer’

5. CLEANING AND ANCILLARY REPAIR WORKS

5.1 Cleaning

5.1.1 General Considerations

The recommendations in this section follow those of BS 8221 – the British Standard Code of Practice on Cleaning and Surface Repairs of buildings, these notes and the code must be followed exactly in terms of methods and precautions and any deviation from such methods and precautions only carried out with the express approvals of an architect or surveyor. This is particularly important with older buildings – and most of the buildings requiring this sort of treatment are going to be older – since cleaning carelessly executed has caused irreversible damage.

Cleaning may be advisable either for aesthetic reasons or for maintenance of the building fabric. Under the heading of aesthetics we list the following.

(a) to reveal the nature, colour or details of an existing building,

(b) to unify the appearance of a building that has been altered, extended, or repaired,

(c) to facilitate the choice of materials for a proposed extension, or for repairs,

(d) to reflect more light on to other buildings

(e) to promote personal or civic pride.

Under the heading of maintenance we list the need to remove harmful deposits from the fabric of the building and the need to expose defects in order to establish the nature and extent of the repairs. Most jobs will involve both aspects.

Repairs, (and under this heading repointing is included), may be again considered as being for purely aesthetic reasons or for the preserving of the structure. The latter comprises the repair or replacement of elements that have suffered damage, and in particular:

a) restoring the weather resistance of the building,

b) repairing surface defects likely, in the long run, to effect the stability of the
structure or of parts of the structure,

c) replacing defective fixings such as wrought iron cramps and ferrous metal components,

d) reinstating the surface of the building after structural repairs.

5.1.2 Buildings of Architectural or Historic Interest.

Where the building concerned is statutorily listed or in a conservation area, the local authority should be consulted.

This will be the planning department of the district council for the area in which the building is situated (this is not a matter dealt with at county planning level), most planning authorities now employ a conservation architect to give expert advice to the public, to designers and contractors and to the council committees on aspects of listed buildings, conservation areas, and historic buildings generally.

In some conservation areas, the local authority may discourage or prohibit the cleaning of individual buildings, as to conserve the uniform appearance of whole streets or areas. Where work on features of historic or artistic importance is being considered, guidance from specialists should be sort, since the general recommendations given may need to be supplemented. Care should be taken not to remove traces of original design or colouring where these may be of architectural or historic interest. Notice to the Department of the Environment of work on buildings scheduled under the Ancient Monuments Acts is required by law.

5.1.3 Choice of Method

There are no hard and fast rules for choice of method in cleaning, different techniques are described below but before discussing these in detail we can look at factors that will all have a bearing on the particular method chosen.

1) Type and condition of surface.
2) Type and condition of material.
3) Amount and type of deposits to be removed.
4) Type and use of building.
5) Location of building.
6) Availability of services.
7) Disturbance to public – dirt, dust, noise and chemicals.
8) Speed of work.
9) Likely weather conditions.
10) Interior work.

5.1.3a Services

Before finally deciding upon a method, it is necessary to check on the availability and adequacy of the water, drainage and electrical services. In general, cleaning and repair work may be carried out using clean tap water (potable water). The code advises the use of de-ionised water for delicate work.

5.1.3b Protection of buildings & safety of personnel & the general public.

Before any cleaning or surface repair work is begun, it is necessary to consider what protection or temporary support the building will require. The following are the main points to think about.

a) Before cleaning it is essential to seal temporarily any fractures and similar structural defects and to protect joints to prevent entry of cleaning agents.

b) External fixtures, such as illuminated signs and name plates, should be protected or, preferably, removed and stored for subsequent replacement, unless otherwise specified. The electricity supply to these features should be disconnected.

c) Decorative fixtures such as balustrades, cornices and carved ornamentation, may need to be protected against damage.

d) Where necessary, scaffold tubes should be capped with plastic caps to prevent rust staining to the face of the building and/or to avoid the tubes becoming traps for water or cleaning fluids which may then be hazardous during the dismantling of the scaffold.

e) During the course of the work the debris should be collected from each lift of scaffolding and not swept off or thrown to the ground, as this can damage other parts of the building.

f) When cleaning interior surfaces, special precautions may be necessary to protect other parts of the structure such as floors and woodwork, and the contents of the building, eg. electronic equipment, monuments, organs and paintings.

5.1.3c Water.

Each of the cleaning methods may present other problems and these are now considered in relation to the methods. Where WATER CLEANING is to be used, usually the normal rainwater drainage system is adequate to take the amount of water used in cleaning the exterior of the building. However, before the work is started, the system should be inspected to ensure that it is of adequate capacity and free from blockages. Before starting work inside a building, particular consideration should be given to the disposal of waste water. In all cases consider the environment in relation to chemicals used.

5.1.3d Abrasive.

Where AIR or WATER ABRASIVE CLEANING is proposed, before starting all windows should be protected with a polyethylene coating, applied in accordance with the manufacturers instruction, and also a rigid sheet material, eg. hardboard, where necessary. Care should be taken when fixing or removing these protective materials. Hopperheads, rainwater gullies and outlets should be covered and protected from the accumulation of spent abrasive. Similarly, intake fans and air inlets should be protected. Spent abrasive should be collected and cleared at regular intervals.

5.1.3e Chemical.

With CHEMICAL CLEANING AGENTS Protective measures needed may vary according to the type of agent used. Products based on hydrofluoric acid affect glass and polished surfaces, such as marble and granite, such surfaces should be protected carefully with polyethylene sheeting or a peelable coating applied in accordance with the manufacturers instructions. Exposed metal and paintwork should be protected when acid or alkaline cleaning agents are used; care should be taken to avoid staining of the building façade by run off from metal scaffolding.

5.1.3f Weather Conditions.

WEATHER CONDITIONS must be considered, “………..all wet methods of cleaning and surface repair, including repointing, should be suspended, or suitable protection provided, if there is a risk of the building fabric becoming frozen whilst saturated with water, however, dry cutting out in preparation for surface repairs may proceed.”.

5.1.3g Health Hazards.

The HEALTH HAZARDS in using these techniques must not be underestimated. It is the responsibility of the licencee to ensure that operatives using caustic chemicals are aware of the dangers, are provided with protective clothing, eye protection, and are fully aware of and equipped to put into action first aid measures. Team leaders are responsible for ensuring that safe modes of working are adopted, that any first aid ointments, etc…., are available on site and that the way of using them is understood. Skin burns, splashes into eyes or accidental swallowing of caustic substances will usually need immediate medical attention from the nearest hospital casualty department, the location of the nearest such department should be part of the preliminary organisation before starting work on site (not that every hospital operates a casualty service).

Grit blasting methods of cleaning, carelessly carried out can lead in the long term to industrial disease (in particular silicosis) due to breathing in of fine particles of silica (the principal component of most sands), protective clothing and respirators must be worn and the breathing in of fine dust particles minimised. Particular care is needed with any dry process to avoid dust being carried on the air to areas where the public have access. See Health & Safety section.

5.1.4 Materials to be CLEANED.

5.1.4a Stonework.

With STONEWORK it is very important to identify which of the types of natural stone have been used in facing the building to be cleaned (or indeed whether artificial or cast stones have been used). Stones are mixtures of different minerals (chemicals) and it is the way that these materials react to cleaning chemicals (and do not forget that water is also a chemical) that determines which sort of treatment should be applied to a particular case.

LIMESTONES are particularly common as wall facing throughout the country and are very typical on the great oolitic limestone band that runs across England from East Devon through the Cotswolds and the Lincolnshire wold and up into North Yorkshire. These stones should be given one of the water treatment methods described below and should not be treated with acid which will dissolve the limestone. Cleaning can bring out a brown stain on the face of the stone. Nothing can be done to remedy the staining, although it will slowly disappear with time, particularly when exposed to strong sunlight. Dry or wet air abrasion methods are suggested for HARD limestones (generally not the oolithic stone but those associated with coal bearing strata); these techniques are not recommended for the softer limestones. MARBLE is a form of limestone and again should not be treated with acid, minimum amounts of water should be used and poulticing techniques may be appropriate for small items in marble. ALABASTER is a form of gypsum, is very soft and water soluble – this is not something which will come up very often. FLINT is made of pure silica and can be cleaned with water, if necessary this can be cleaned with dilute hydrochloric acid, particularly, perhaps, to remove cement haze after repointing. GRANITE may be either polished or left with a rough hewn face. Polished granite will need very little treatment beyond washing; abrasive methods and caustic chemicals may destroy the polish on the face – it is not practicable to reinstate this in-situ. Rough granite can be cleaned using abrasive techniques or chemical methods based upon hydroflouric acid. The latter is exceedingly corrosive and should only be used under expert guidance. This manual does not aim to give such guidance. Treatments for SANDSTONES are similar to those used for unpolished granites though care is needed in using abrasive techniques on some softer sandstones and in using water treatments on some iron rich sandstones (there is a tendency to induce “rust staining” on the surface) subjected to anything more than washing with detergent and leathering off. Artificial stones are best treated with water, although this may create a somewhat patchy finish. If necessary hydrochloric acid can be used. Abrasive methods could also be used though care is needed to avoid exposing the common concrete core found in most artificial stones.

5.1.4b Brickwork

With BRICKWORK the variety of materials used is less. As a general rule, abrasive methods should be avoided except where other methods have proven unsatisfactory, eg. under projections. Where brushing is required to assist in the removal of dirt from soft carved or moulded brickwork, it should be carried out lightly using only fibre brushes (that is never use wire brushes).

Cleaning clay brickwork can remove some or all of the surface, depending on the severity of the method used. This may have an unacceptable effect on durability and appearance. It should be noted that clay bricks may have a uniform colour throughout their body or they may have a different colour on the surface or a surface coating, eg. sand faced bricks.

Where the binder of the material to be removed is organic, the use of neutral liquid detergents should be tried first. This applies particularly to heavy oil residues. If detergents are found to be ineffective, other chemical cleaning agents may prove more satisfactory. Whatever agent is chosen, the brickwork should, if necessary, be put into sound condition. Water spray processes are seldom satisfactory when used on their own but may be used for cleaning very soft brickwork. Whilst there is always a risk of efflorescence using “wet” methods, this can be minimised by ensuring that the brickwork never becomes saturated.

Some clay bricks contain soluble iron, manganese or vanadium salts. Depending upon the age of brickwork, iron, manganese or vanadium salts may still be active, and staining could result from “wet” methods of cleaning which saturate the brickwork. Therefore a trial area should be cleaned. If staining of this area occurs then a chemical analysis should be carried out to determine the nature of the stain and hence to select an appropriate method for cleaning the brickwork eg. an agent based upon hydrofluoric acid and orthophosphoric acid in the correct proportions has been found to be effective in treating iron stains.

Any efflorescent salts should be allowed to weather away naturally or should be brushed off with a dry fibre brush.

CALCIUM SILICATE (sand – lime or flint – lime) Brickwork. Calcium silicate brickwork may be cleaned by water spray, air abrasive, water abrasive or chemical methods. Although cleaning can remove some or all of the surface, this is not a problem in practice, owing to the uniform nature of the material. However where chemical methods other than detergents are to be used, specialist advice should be sought…

GLAZED BRICKWORK. Soiling of glazed brickwork may occur either on the surface or under the glaze. Usually, surface soiling may be washed off using a water rinesable neutral liquid detergent. Where soiling exists behind the glaze this is usually the result of dirt penetration through crazing of the glaze or, sometimes, the result of dirty water coming through the brickwork behind the glaze. Such soiling cannot be removed. Any attempt to infiltrate a chemical through the glaze to clean from behind is almost certain to damage the glaze.

5.1.5 Deposits to be removed.

The deposits to be removed may vary from thin surface soiling to deposits that penetrate to a depth of as much as 50mm. Normally the deposit consists of airborne dirt, often bound together as well as to the masonry surface with either calcium sulphate (gypsum), or silica depending upon the substrate. Typically the former – Gypsum – comes from the weathering of limestones and calcium silicate bricks, and the latter – Silica – from the weathering of sandstones or clay bricks. It is important to identify the substrate and the material to be removed, since these are two of the factors that will determine the method of cleaning to be adopted. Toxic materials such as old lead paint have to be treated in such a manner as to satisfy the appropriate safety legislation. A chemical analysis may be helpful in identifying the material to be removed.

5.1.5a Gypsum.

GYPSUM is soluble in water so that water cleaning methods would normally be sufficient for dealing with deposits of this type. Where the substrate is sufficiently hard, air and water abrasion may be used if water cleaning proves too slow, remember that abrasive methods should not be used on soft materials and, when you are dealing with soft stones or bricks, you will have to accept that it is going to be a slow job and therefore one that is more expensive. It is always worthwhile bringing this to the attention of the client when tendering for cleaning work. It would be unrealistic to compare a price for cleaning using water and gentle brushing, with one based upon some form of grit blasting, make sure your client knows what method your price is based upon.

5.1.5b Silica.

SILICA is insoluble in water but soluble to varying extents in different acids. If water cleaning methods fail to remove the dirt deposits, abrasive methods could be used. Chemical techniques based upon hydrofluoric acid can be used. As mentioned above this is a highly, corrosive and caustic acid and it should only be used with expert guidance and by reliable operatives.

5.1.5c Lime Staining.

LIME STAINING often shows as white streaks on brickwork spreading out from below a joint in a coping or cill or from a weephole. This is caused by the action of water (usually rainwater) saturating the brickwork and dissolving lime that is present in the mortar joints (even portland cement contains a proportion of free lime so this can occur even when a comp mortar has not been used). CALCIUM CARBONATE (the chemists name for chalk) deposits are found most commonly as thickish white encrustations below pipes, gutters and the like, where over a longish period water has been leaking fairly slowly and when evaporating to leave the “hardness” behind, these are also commonly called lime deposits because of the colour. Scrubbing with a fibre brush and water should be tried first of all, often this will dissolve and remove lime staining, the harder chalk deposits are not particularly soluble in water and generally will require treatment with dilute hydrochloric acid. This can also be used for persistent lime staining. The working method is described in detail below.

5.1.5d Mortar Spillage and Grout runs from Concrete.

MORTAR SPILLAGE AND GROUT RUNS FROM CONCRETE are most likely to occur in new building work often as a result of poor control during construction. You are most likely to come across this if you undertake a “clean down & point” job where the brickwork joints are raked out as the wall is built. Again hydrochloric acid treatment is used. If particular grout runs only down face brickwork are to be cleaned, it is as well to clarify with the client that in cleaning the stain you may end up with a streak down the brickwork that is of a slightly different colour from the rest of the work. Where the client is a contractor who is having to do this at his own expense because of his own mistake, this may lead to arguments over payment, retentions, etc. A better approach (and one that was adopted when this practice was more common) is to clean the elevation generally so that the patchiness is avoided. Metal scrapers or brushes should not be used since they will mark the surface of most bricks and in particular sand faced or rustic bricks.

5.1.5e Efflorescence.

EFFLORESCENCE has been discussed in a previous section. It is most usually seen on new external brickwork in the early spring as the weather improves and starts evaporating water absorbed over the winter. Brush off with a soft brush and collect the salts, if they are allowed to blow away when you are cleaning high up, they may blow back on to the wall lower down and be reabsorbed. Normally it is not advisable, wrong in fact, to use water since this will dissolve the salts on the surface, be absorbed back into the wall and the process will be repeated. It is better to leave any final traces of the salts that adhere to the wall to weather away naturally. The problem can also occur with internal facing brickwork that had become saturated during construction when open to the elements. Again brush off what can be removed by this method if the client wants the remainder removed, this can be done by careful use of water with a sponge to absorb the water and prevent it going back into the wall. Even with care some water is going to be absorbed back and efflorescence may recur. In discussions with the client this should be made clear and perhaps the price should show a separate item for return visits if necessary as the client may require.

5.1.5f Paint and Limewash.

PAINT and LIMEWASH: Limewash (whitewash) was a very common wall treatment, now superceded by distempers and emulsion paints. Sometimes the removal of old unwanted outbuildings leaves exposed areas of limewashed walls from which the wash is to be removed. Crude whitewash was merely a lime and water suspension and dissolves easily in water, often the best advice is to leave such walls to weather back to the original brick or stone face. Sometimes tallow and other binding agents would be added to the limewash to increase its durability, these can still be removed by washing and scrubbing with water but may require more time. Distempers and later emulsion paints use less water soluble binder but the treatment is as before. Oil paints are bound with oil or resins and are therefore not soluble in water. There is a tendency where they are applied to masonry surfaces for areas of the paint to lose bond to the background and these pieces come away very easily, adjacent pieces firmly adhering to the background, will need chemical strippers for their removal. It may be worth trying caustic soda or caustic potash on small trial areas as they may be effective.

Another possible treatment is to use a needle gun powered by compressed air, large areas may be treated more economically with abrasive techniques.

5.1.5g Oil and Grease, Tar Stains.

OIL and GREASE, TAR STAINS: these can be very difficult to deal with satisfactorily and it should be made clear to a client that the process may be expensive, time consuming and then not entirely successful. Neutral liquid detergents should be used for degreasing and not powdered detergents since the latter contain large quantities of soluble salts which it would be unadvisable to put into the wall. Volatile solvents such as white spirit, petrol, etc. tend to dissolve the stain and then spread it further into the wall.

A technique known as poulticing may be useful in drawing out the stain.

Tarry stains are often in evidence around chimneys and come from soot deposited on the inside (flue wall) of the chimney. Porous parging (a mortared layer plastered on to the inside of the chimney allows water to penetrate during the winter, particularly when there is only a half brick thickness around the flue and dissolve the soot. This water evaporates away during drier weather leaving soot/tar deposits on the surface. It is questionable whether it is worth trying to remove these deposits, for unless the chimney construction is improved, the staining is likely to recur. This problem is commonly associated with changes in the type of appliance that the chimney serves, the change from an old fashioned open fire to slow burning appliance from the fuel consumption point of view, but means that the flue gases are less hot since they have given more heat into the room and are therefore more liable to condense in the flue depositing moisture on the inside of the flue to add to the moisture that penetrates from outside. Treatment is as for oil and grease stains.

5.1.5h Metal Run Off Stain.

RUN OFF STAINS from METALS: typical examples are rust stains from iron and steel work and the very characteristic green stain from copper and bronze. Treatment requires special solvents, tend to take a long time and as with tar stains are likely to recur.

5.1.5f Moss, Algae and Lichens.

Algae are almost microscopic plants which tend to grow in winter on the north facing walls, producing a characteristic green haze over the wall surface. They tend to disappear from the spring onwards when the weather becomes drier and normally would not require treatment. Lichens are plants too and grow in small scaly, often yellow coloured patched on walls and roofs. These living organisms produce a mildly acidic effluent which attacks limestone and cementitous materials – mortar, concrete tiles, artificial stone and pre-cast concrete components. Often their appearance particularly on stone, is considered to add to the attractive variation in colour and texture in weathered stone. If removal is considered necessary, the surface should be scraped (again wood and non-metallic) to remove as much as possible mechanically A toxic wash applied subsequently will kill off any part of the plant that is within the surface of the wall material. Common bleach is often successful – dilute 1 part of bleach to 4 parts water. BRE digest no 139 gives details of other treatments.

5.1.6 Cleaning Methods.

In the main it refers to the cleaning of the external surfaces of buildings, similar methods are appropriate for cleaning internal surfaces, usually after vacuum cleaning and requiring, of course, much greater attention to the protection of surrounding areas.

5.1.6a Brushing.

BRUSHING: brushing may be used on its own, eg. for removing efflorescent salt using fibre brushes, or more commonly with waterspray or chemical cleaning using fibre or bronze brushes. Steel wire brushes should never be used as the broken ends of the wire are likely to cause rust staining.

5.1.6b Water spray.

Fine, nebulous (misty) sprays of clean cold water are used to soften the dirt deposits, which are afterwards brushed off. In certain cases it may be necessary to rub surfaces with a soft grit stone as well to remove encrustations, taking care with stonework not to damage any of the original tool marks which give the particular texture to certain classes of stonework. Excessive water should not be used, only sufficient being applied to ensure that the surface is kept wet. Various systems have been developed which make use of specially designed jets to cover a wider area with the same amount of water. For cleaning some areas it may be advisable to use only a bucket of water and a brush, so as to minimise the amount of water applied to the wall, especially when dealing with delicate features, mouldings, etc. Care should be taken to avoid water getting into cracks, etc., particularly where damage to plaster or to woodwork may result.

5.6.1c High Pressure Water Lance.

The high pressure water lance is a useful way of removing stubborn areas of dirt and organic growth, particularly when used in conjunction with water spray cleaning. Care is needed to select water pressure and type of nozzle to ensure that the fabric of the wall is not damaged. Straight tip (pencil point) nozzles should not be used. The water lance is also used to rinsing off after wet abrasion or chemical treatments.

5.1.6d Steam Cleaning.

This is not a method that is likely to have wide application nowadays because of cost and variable quality of the finish achieved. However when used in conjunction with suitable solvents, it can be useful for the removal of certain deposits, such as bitumastic paint, oil, grease and chewing gum(!).

5.1.6e Dry Blasting.

Abrasives are blown onto the surface at a suitable pressure by means of a compressed air jet. The equipment consists of an air compressor and a suitable pressurised storage put together with hoses and suitable nozzles. The traditional abrasives used are sand and flint. However these contain free silica which can create a health hazard both to the user and to any other persons in the vicinity; alternative materials, such as mineral slags, are available. It is essential to choose a type and a grade of abrasive to the type and condition of the surface to be cleaned.

Dry air abrasion must be used with caution as it can cause damage to arrises, carved work, glazed brickwork and soft bands present in some stones. In addition to the health hazard from the abrasive used, with brickwork and other siliceous materials there is a further problem from the fine silica dust abraded from the surface of the work being cleaned.

5.1.6f High Pressure Water Abrasion.

High pressure water abrasion is available but care must be taken to its suitability.

5.1.6h Mechanical Abrasion.

Spinning off with power tools, using carborundum discs on flat surfaces, removes dirt and the weathered face in a single operation. Great care should be exercised since there is considerable risk of damaging the surface, especially mouldings and there is again a considerable health risk from inhalation of silica. This is now regarded as an obsolescent method that has been superceded by others just described.

5.1.6i Acid Treatments.

Only the use of dilute hydrochloric acid (spirits of salt) is covered in these notes. Others are used (hydrofluoric acid is one that has been mentioned a few times in the previous notes), specific advice should be sought if it is proposed to use these substances.

For cleaning buildings a 5% solution should be tried first (add one part of concentrated hydrochloric acid to nineteen parts of water – ALWAYS ADD ACID TO WATER, NEVER ADD WATER TO ACID), if stains are persistent then a 10% solution can be tried (one part of acid to nine parts of water).

The wall to be treated must be damped down with water first to prevent excessive absorption of the acid. The acid should be applied with a soft bristled brush (like a painters grass brush) – stiff bristles will cause the acid to “flick” perhaps into your eyes. Goggles and gloves must be worn and any splashes on to the skin must be doused with plenty of fresh water which should always be on hand when acid is being used. Any splashes in the eyes should again be doused in water and medical help sought immediately.

The acid should fizz quite strongly when first applied, gradually dying away as the acid is neutralised. Further applications may be necessary, and upon completion the wall should be thoroughly washed to remove any traces of the acid.

5.2 Treatment of Walls with “Waterproofer”

On occasion we may be asked to apply waterproof treatments to external walls in addition to repointing of the walls, probably with a view to reducing dampness due to rain penetration through walls that are often of inadequate construction anyway.

Colourless “waterproofers” are generally silicone based. These substances are properly called ‘water repellents’ (thus not intended to water proof anything).

Although it is assumed that normally a wall will have been repointed and repaired before you apply water repellent solutions, it should be remembered that any open cracks are likely to be subjected to an increase in the flow of water since the treatment will have reduced the absorption over the wall surface generally. The water repellent should be applied to the whole of the wall surface (ie bricks and stone and mortar joints). The colour of the wall should not be affected, some repellents include a dye which enables to know where you have applied the repellent – this dye fades rapidly in daylight. The effective life of the treatment is uncertain and depends upon factors (such as weather and type of material) found on a particular job. Like painting, however, one is probably talking about the need to repeat the treatment every few years. Initially the wall will show a marked tendency to shed water : this may wear off after a few months as the superficial part of the treatment is eroded. However, the repellent absorbed within the surface pores of the brick will continue to reduce the absorption into the wall.

Application should be to the manufacturers instructions, normally to a cleaned surface, free from algae or other organic growth.

Care is needed in applying these treatments to stonework since the repellent layer near the surface may reduce evaporation and lead to spalling of the stone from salt crystallisation behind the surface (cryptoflorescence) : this can also happen with some soft bricks.

Try to get manufacturers' advice in writing in all cases.

The above information should not be taken as recommendations for any individual contract/project and are guidelines only. Consult your local licencee for advice on the projects in your area.

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