Walls

Before the introduction of the railway to Wales from the mid-nineteenth century onwards, the construction of buildings was generally dictated by the availability of local materials. Transportation by road, sea or river was expensive and imported materials, including Bath stone, were used only on high-status buildings, such as gentry houses and churches.

This reliance on local materials led to the development of quite separate and distinctive regional building styles across Wales. Timber-framed buildings, for example, can be found in abundance in the Marches, along the border with England, due to the ready supply of mature oak trees up until the end of the eighteenth century. Styles of timber-framing varied from simple box-framed panels to highly ornate close-studding. By contrast, stone of different types is the principal building material of north-west, south-west and south-east Wales. Yet each type of stone has its own characteristics, which give rise to a diverse range of building styles. The neat, banded stonework that can be seen in Cardigan, for example, is very different in appearance to the course random rubble walling of Eryri (Snowdonia), but each looks right in its own setting.

The way in which stone was dressed and finished varied with the type of stone, but also with the status of the house, a finer finish denoting a greater investment in the building process. Changes in fashion also influenced the appearance of stonework, as the widespread use of limewash or render gave place to a taste for exposed stone.

More limited in its distribution was the use of earth (clom) in building, where neither timber nor stone was readily available. Mud mixed with straw was a durable material, provided it was well protected, usually with limewash as well as a good roof.

Mass production and the introduction of the railway diluted the dependence on local materials, but nonetheless regional variety proved resilient. Manufacturers, such as Edwards of Ruabon, were a major influence on Victorian and Edwardian architectural style throughout Wales and beyond. Brick and tiles were not widely used here until this time, but the vast range of often highly decorative, yet standardized products that became readily available provided a cheap alternative to local materials. Towns such as Llandudno and Llandrindod Wells, for example, illustrate clearly the versatility and durability of fired clay. Despite this, locally sourced materials — especially building stone — continued to be used throughout the nineteenth century, and there are also significant regional variations in the way that mass-produced materials were used.

What to look for: 

Vegetation growing in walls

Suggested action: 

Remove vegetation at the earliest possible opportunity.

Self-seeded shrubs, saplings and ivy, can cause severe damage if left unchecked. Invasive growth that cannot be removed by hand without damaging the mortar joints should be treated with a systemic weed killer and left in place to die and fall away. If you are mixing up the weed killer from a concentrate, add a little washing up liquid to act as a wetting agent.

Growth of vegetation often signals that other maintenance work is needed to eliminate cracks and holes where seeds can lodge.

Ornamental climbing plants, such as wisteria or hydrangea, can encourage damp and the roots of well-established specimens can undermine the foundations of a masonry wall, particularly where they are shallow. Although owners may be reluctant to remove mature specimens of ornamental plants, it may be unavoidable if they create serious maintenance problems.

What to look for: 

Signs of damp on exterior or interior walls

Suggested action: 

Inspect your building carefully inside and outside for signs of damp including moist patches, water or rust staining, and growth of mould, mildew or algae. Identify the cause of the damp and treat accordingly

Many damp problems can be resolved by simple maintenance, so be systematic in your inspection of the building. Whenever damp is found, it is essential to identify the cause correctly and tackle it promptly.

Damp is frequently misdiagnosed, leading to sometimes costly and ineffective interventions being made. Installing an injected damp-proof course or ‘tanking’ the inner face of external walls, for example, is often recommended as the solution to rising damp. While this may be the only option available in certain cases, rising damp is rarely the real cause of the problem, which could be as simple as the external ground levels having risen above the internal floor level or above underfloor vents.

Carefully inspect walls internally and externally, including in the roof space if necessary, to find the source of the water. If moisture is trapped behind impermeable materials, it will travel through the wall, emerging wherever a more permeable surface is found. This will usually be on the internal face of the wall. As a consequence, the damp patch may not necessarily be at the site of the problem.

Common causes of damp include:

• defects in the roof, chimneys or rainwater disposal system 

• defective pointing or loose masonry 

• raised ground levels, blocked underfloor vents and airbricks 

• condensation 

• damp in cement and other impermeable materials 

• damp in cavity walls 

• presence of hygroscopic salts.

In old buildings, electric moisture meters will almost always give high readings in walls at low level due to condensation. Yet, these readings frequently lead to a misdiagnosis of rising damp. If you cannot find the source of the problem and you need further advice, contact an independent surveyor specialising in damp and timber decay, rather than a company selling damp-proof treatments. This will help to ensure that the diagnosis is correct, which can save you from the expense and disruption of unnecessary ‘remedies’.

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What to look for: 

Causes of damp — Defects in the roof, chimneys, or rainwater disposal system

Suggested action: 

Check the condition of the roof, chimneys and rainwater disposal system and correct any faults.

Defects in these areas are the most common causes of localized damp problems. 

• roofs 

• chimneys 

• rainwater disposal systems 

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What to look for: 

Causes of damp —Defective pointing or loose masonry

Suggested action: 

Check the condition of walls generally, paying particular attention to parapets, copings and raised gables. Replace loose stones and repoint with lime mortar as necessary.

Loose or missing stones and open masonry joints can allow water to enter. If the problem is isolated, rebed and repoint individual stones as necessary. Most buildings constructed prior to the early twentieth century were built using lime mortar. It is important to use matching materials for subsequent repairs. Deep holes or wide joints in stonework should be filled using mortar and small stones, known as ‘galettes’ or ‘pinnings’, before being pointed up.

On parapets, copings and raised gables, if the damp is persistent, it may be necessary to install a lead damp-proof course to give added protection to the wallhead. This will probably require the rebuilding of the top few courses of masonry or the re-laying of coping stones.

Avoid products that claim to seal or waterproof masonry as they are rarely effective and they can make the problem worse by trapping moisture in the stone or brickwork.

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What to look for: 

Causes of damp — Raised ground levels, blocked underfloor vents or airbricks

Suggested action: 

If possible, make sure the external ground level is below the internal floor level and clear any obstructed underfloor vents and airbricks.

Remove vegetation and ensure that soil does not build up at the base of walls or above the level of under-floor vents. Avoid storing materials close to the building as this can reduce ventilation.

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What to look for: 

Causes of damp — Condensation

Suggested action: 

Control humidity by increasing the amount of ventilation through opening windows or using extractor fans.

Condensation is often misdiagnosed as penetrating damp. It is caused by moisture in the atmosphere condensing on the coldest surface of the room.

A small amount of condensation will not usually cause any harm as it simply evaporates once the surface warms up. However, in poorly ventilated spaces or in buildings that are only intermittently heated, condensation is more likely occur frequently or over a prolonged period of time. This can cause the growth of mould and mildew, peeling paint and the decay of damp surfaces.

Increasing the temperature will not solve the problem alone. Indeed, it can make the condensation worse as the ‘relative humidity’ of the atmosphere will be increased. Warm air can carry a larger amount of water vapour than cold air, thereby increasing the amount of water available to condense on cold surfaces.

Try to control humidity by avoiding big fluctuations in temperature, removing moisture-laden air from kitchens and bathrooms by opening windows or using extractor fans, and increasing ventilation generally.

If the condensation is forming in patches, check whether there is an underlying problem with moisture penetration, such as a split downpipe, that is causing that part of the wall to be colder than elsewhere, thereby encouraging water vapour to condense in that location.

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What to look for: 

Causes of damp — Moisture trapped by cement or other impermeable materials

Suggested action: 

Replace impermeable materials with lime products.

If there is no obvious source of moisture, such as a broken downpipe, the damp problem may be due to the effects of impermeable materials.

In traditional buildings with effective drainage and solid wall construction using earth or lime mortar, damp is controlled by the ability of the walling materials to absorb small amounts of water from the ground, or atmosphere, and to release it again harmlessly through evaporation. The thickness of the structure prevents moisture from penetrating the full depth of the wall. Additional protection is usually given to the exterior of the building by lime render or successive coats of limewash. These materials act like an overcoat, rather than a mackintosh, as they are also breathable, allowing any moisture within the structure to escape.

Internally, small amounts of moisture are absorbed through porous finishes, including limewash or distemper (an old form of paint made from whiting and glue) over lime plaster. Natural ventilation, provided by open fires and unsealed windows and doors, allows moisture to escape again without causing problems.

By contrast, modern building techniques rely on moisture barriers and seals to prevent moisture entering a building. Where damp is present in an historic building, it is often due to the introduction of impermeable materials, such as acrylic-based paints and gypsum plaster, with the result that the solid walls can no longer breathe. Modern cement renders and cement pointing are particularly harmful. Cement is hard, inflexible, brittle and impermeable. Cement render has a tendency to crack and craze, and moisture can be drawn into the underlying material through capillary action. Once inside, the moisture is trapped, causing failure of the render and deterioration of the walling material. The action of frost and the presence of salts dissolved in the moisture only serve to hasten the decay. If the problem is severe or longstanding, the moisture can penetrate through the depth of the wall to rot timber lintels and the ends of joists and roof timbers.

If cement or other impermeable materials are the cause of the problem, they should be removed if possible and replaced with lime products. Similarly, the installation of cement floors and damp-proof membranes can change the environmental conditions, forcing moisture into the walls that would otherwise have evaporated through the floors.

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What to look for: 

Causes of damp — Debris in cavity walls

Suggested action: 

Carefully remove one or two of the bricks, remove the debris and replace the bricks with matching mortar.

If no other cause for damp on the inner face of a cavity wall can be identified, it may be the result of builders’ debris trapped between the two brick skins. Debris in the cavity acts as a bridge allowing moisture to reach the inner face of the brickwork. Once this has been correctly diagnosed, the only long-term solution is to carefully remove one or two of the bricks, remove the debris and rebuild the wall.

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What to look for: 

Causes of damp — Hygroscopic salts absorbing moisture from the air

Suggested action: 

Damp can cause salts present in masonry to move to the surface. Eliminate the source of the damp and brush off salt christals as they form.

Such salts can continue to be damp, even after the original moisture source has been removed. This can be a particular problem with disused chimneys, causing damp and staining on the inner face of the chimney-breast.

In dry conditions salts will often crystallize as white fluffy patches on the inner face of the wall. These should be brushed, rather than washed, off. If the problem is serious, seek advice from a conservation architect or surveyor.

What to look for: 

Damaged or deteriorating brick, stone or terracotta

Suggested action: 

Replace isolated damaged stones, bricks or terracotta with matching replacements. Bed and repoint with matching mortar, which in most cases will be lime based

Stone, brick and terracotta are subject to the action of rain, wind and frost, and different materials vary greatly in their durability.

They are traditionally laid and pointed using lime mortar that is slightly weaker than the building material. It is flexible, allowing the structure to accommodate small movements over time. It is also permeable, allowing any moisture and dissolved salts to freely move into the joints where the water can readily evaporate and the salts crystallise without causing significant harm. Although lime mortar acts as a sacrificial element and the masonry will need to be repointed from time to time, this is far easier than replacing the building material itself.

Replacement of lime mortar with cement can cause severe erosion of brick, terracotta and stone by trapping moisture. Since cement is relatively impermeable, trapped water can be drawn into more porous stones or bricks and, through frost action and other processes, cause their exposed surfaces to spall or flake off.

Cement is also hard and inflexible, making the structure too rigid. It will crack under pressure, but if the brick or stone is weaker than the mortar, as is often the case, they will snap instead.

Terracotta is formed of moulded, hollow blocks, which are filled with concrete and pinned together with iron or steel fixings. It is an extremely durable material provided that it remains watertight. However, once moisture gets inside, the fixings can rust and expand, causing the blocks to crack. The surface of the blocks can also be damaged as a result of inadequate firing or overly complicated moulded decoration, which can break off. It may be possible to repair cracks using epoxy adhesive, but badly damaged blocks may need to be replaced with replicas. Replica terracotta blocks can be obtained from specialist suppliers, but seek advice on the most appropriate method of repair.

Isolated damaged stones, bricks or terracotta blocks can be carefully cut out and new pieces bedded in using lime mortar. Ensure that the replacements are a good match for the original material in terms of size, colour, finish and strength.

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What to look for: 

Damaged or missing pointing; loose masonry

Suggested action: 

Replace damaged or missing pointing and re-bed loose masonry with lime mortar.

Defective pointing and loose masonry can encourage damp, and repairs should be made using lime mortar.

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What to look for:

Signs of movement, bulges and cracks

Suggested action: 

If cracks or bulges have recently formed or are increasing in size, consult a structural engineer to determine the cause and take necessary action.

Many old buildings will have undergone a period of settlement shortly after construction and will have reached a state of equilibrium over time. Cracks may seem alarming, but the movement may be an old problem. Dust tends to settle in old cracks over time darkening their appearance, whereas new cracks tend to have clean faces and may contain fragments of masonry or plaster.

Be aware of previous repairs that may have been undertaken using inappropriate materials or intended only as short-term solutions. Such work will need to be carefully monitored. Check also for cracks and signs of movement, particularly between different materials or near previous alterations, such as the site of removed walls, new doorways or an inserted window. Hairline cracks are often due to shrinkage of the plaster, but larger cracks may indicate a more serious problem.

Try to identify the load bearing elements of the building and the cross walls that help to tie the structure together. From the outside, assess how vertical walls are by eye and look inside the building for gaps between the edge of the floorboards and the external wall, as well as cracks in the plaster where the external wall joins the ceiling and any internal partitions. Cracks in these areas may indicate the outward movement of the wall. Cracks will frequently be seen at the junction between original walls and later extensions due to differential settlement, but these are not necessarily problematic unless they are severe.

Cracks over the top of an opening can suggest failure of the lintel that supports the masonry above, and these should be investigated further. However, fine cracks in render around a blocked opening are probably due to differences between the background and infill material, and are not likely to need attention.

Take notice of changes around the outside of the building that may affect the environmental conditions. A tree growing close to a wall, particularly in clay subsoils, for example, can affect the ground conditions by removing moisture around the foundations, causing shrinkage. On the other hand, the removal of a mature tree can add moisture that would otherwise have been taken up by the roots, causing the soil to swell. Either extreme can cause movement of the foundations and cracks in the wall above, but in most cases trees are not the real culprits. So always seek advice from an experienced tree surgeon and structural engineer before felling a mature tree, and check first whether it is protected by contacting the local planning authority. If a wall is being affected by tree roots, it may be possible to prune them and to install root barriers to prevent further problems in future, rather than felling the tree.

A far more common cause of settlement is faulty drains, as the leaking water will gradually wash away the soil around the foundations. This can affect internal, as well as external walls, but the fault may not become apparent until the damage is done. The drainage problem must be corrected, but the wall may also need to be underpinned in order to regain its structural stability.

One possible cause of bulges in cavity walls might be failure of the wall ties. These were introduction from about 1900 and were used to tie independent inner and outer leaves of brickwork together across a hollow core. This provided protection against penetrating damp and the technique is still in common use. However, unlike modern wall ties, early versions used to be made of iron or galvanized steel and are susceptible to corrosion. This can lead to separation of the two leaves of brickwork and ultimately, collapse of the outer face, as it is no longer restrained. Cavity wall insulation can make this problem worse as it can act as a bridge across the cavity, thereby encouraging water to pond around the wall ties, hastening their deterioration.

Rubble stone walls are usually built with two leaves of stonework with a rough inner core of lime mortar, dirt and small stones. The outer leaves of the wall can lose their bond with the inner core for a variety of reasons. Any bulging or outward leaning walls should therefore be investigated quickly by a structural engineer, as it is often possible to ‘stitch’ the structure back together relatively cheaply at this stage using stainless steel rods.

If you are in any doubt about a crack or bulge and the stablility of your building, consult a structural engineer.

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What to look for: 

Cracked, missing or badly repaired render

Suggested action:

Monitor walls for the appearance of cracks, bulges or holes in render; if there are no underlying structural problems, repair with suitable materials

Most stone buildings were historically given an external protective coating of limewash or lime render. They are relatively simple materials to maintain and repair, and should never be stripped as this can encourage damp.

Render was also often applied to timber-framed buildings during the eighteenth century. At this time, the render was often ‘scribed’ or scored to look like expensive dressed stone, but the lack of a recess or ‘reveal’ to the windows and doors, and the shallow depth of the wall are often clues to the underlying material.

Renders were usually lime based, until early cements began to come into use in the early nineteenth century. The early cements were softer and more permeable than modern Portland cement, which can trap moisture in the stone or brickwork. It was fashionable to leave the early cements unpainted, but later patching of cracks using inappropriately coloured sands can be extremely disfiguring and unsightly. In such cases, provided that the render is sound, it may be desirable to paint the render using a stone-coloured limewash or microporous paint. Check with the local planning authority first as this may require consent.

Small cracks in a lime render should be monitored, but they are unlikely to need immediate attention. An application of limewash can help to ‘heal’ them as it is derived from limestone, as is the lime in the render.

Larger cracks may indicate a problem with the underlying structure, and should be investigated. Once more serious problems have been ruled out, larger cracks or missing patches of lime render can be filled.

Cracks of any size in a cement-based render should be tackled at an early stage as they encourage water to be drawn into the underlying material as a result of capillary action. Whereas lime renders can usually be patched, it may be better to remove badly damaged cement render altogether and to replace it with a lime-based mix. The benefits of enabling the building to breathe must, however, be weighed against the damage that can be caused to the substrate by removing hard render. Seek advice from a conservation architect or surveyor on the best approach for your building and on an appropriate render mix that will be suitable for the substrate.

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What to look for: 

Slate hanging - missing or damaged nailed slates 

Suggested action: 

Depending upon their position, replace missing or damaged slates with nails or ‘tingles’ — 1 inch (25mm) wide strips of copper, lead or galvanized steel

Slate hanging is a traditional weather protection for masonry buildings throughout Wales and was particularly popular during the Georgian and Regency periods. It is generally used only on the elevations most exposed to the weather and is often a later addition.

There are two distinct methods of construction. In the most common technique the slates are centre nailed to timber battens, which are fixed to the wall. In the same way that nailed slate roofs are constructed, the slates overlap the ones below, each course being offset to provide an effective seal. Driving rain simply hits the slate barrier and runs off, rather than penetrating into the underlying masonry. The slates can, however, come loose particularly along the top edge as a result of high winds and disturbance by birds. These can be replaced simply by nailing new slates of the right shape and size into position.

Isolated missing or loose slates lower down the wall can be put back into place using copper, lead or galvanised steel ‘tingles’ in the same way as roof slates.

Where a larger area of slates is missing or loose, this is often due to nail sickness or decay of the battens. In either case, the wall will probably need to be reslated, reusing as many of the original slates as possible.

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What to look for: 

Slate hanging – Missing or damaged mortared slates

Suggested action: 

Replace missing or damaged slates using lime mortar.

Slate hanging is a traditional weather protection for masonry buildings throughout Wales and was particularly popular during the Georgian and Regency periods. It is generally used only on the elevations most exposed to the weather and is often a later addition.

There are two distinct methods of slate hanging. In the most common, the slates are nailed to timber battens fixed to the wall. Perhaps an older, and much less common, tradition of slate hanging involves applying a bed of lime mortar directly onto the masonry wall and pressing the slates into it. Nails or wooden pegs are sometimes driven into the wet mortar to provide additional support. The mortar is then cut back flush with the edge of the slate and allowed to begin to harden before the next course is added. Although it is labour-intensive, this technique produces a durable finish and a very distinctive appearance.

Unlike slate hanging on battens, the finish is more irregular due to the method of attachment and the random size of the slates. Examples of mortared slate hanging still survive along the coast of Pembrokeshire, many of which are further enhanced by the later application of a colour wash.

While mortared slate hanging is very durable and more resistant to damage by the wind than slates on battens, individual slates can become detached from the mortar base. These should be replaced quickly using lime mortar, as any failure will allow water to penetrate behind the cladding, which could lead to further losses.

Mortared slate hanging is uncommon. Where complete replacement is necessary, it is essential that the original technique is replicated using suitable matching slates and lime mortar.

What to look for: 

Distorted, split or fractured timbers and opening up of joints

Suggested action:

If timbers have recently twisted, split or broken or joints have opened, consult a structural engineer, conservation architect or surveyor.

Twisting and distortion of timbers frequently occurred shortly after a timber-framed building was constructed as the green oak dried out and shrank. This was a normal occurrence, and timbers with long-stable splits or distortions do not indicate a problem, provided that the joints between the timbers are structurally sound and the building is stable.

Unlike masonry walls, which rely on their mass to support and distribute loads, in a timber-framed building loads are carried principally through the relatively slender arrangement of vertical timber posts and horizontal rails, which are jointed together. The joints are often variations on mortice and tenon joints (where the end of one member is trimmed to fit into a hole cut in the other) or scarf joints (where the ends of each member are bevelled to fit together), pinned together by oak pegs. Diagonal braces provide further stability and once assembled, the structure provides an extremely strong and durable framework upon which to hang weatherboarding or to insert infill panels.

The structural stability of timber framing does, however, depend on the integrity of the whole. The removal of elements to create new openings or the removal of partitions or tie beams (the horizontal timbers of triangular roof trusses), for example, can severely weaken the structure. It is therefore advisable to thoroughly inspect the areas near previous alterations for signs of distress and ongoing movement in the timber framing.

Other than the replacement of missing or defective oak pegs, repairs and strengthening works should be undertaken only by a specialist contractor under the guidance of a conservation architect, surveyor or structural engineer. The work should be carried out in an unobtrusive manner retaining as much of the original timber as possible. Weakened beams can often be left in situ and strengthened using steel plates, while new sections of timber can be spliced in to replace rotten sections.

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What to look for: 

Decayed timbers, fungal growth or beetle infestation

Suggested action: 

Inspect timbers, particularly if coated with impermeable materials, and seek guidance from a specialist timber decay consultant if any signs of decay, fungal growth or beetle infestation are found.

Timber-framed walls are often constructed on top of low masonry walls to raise them off the wet ground. However, moisture can still cause decay, particularly where impermeable materials have been introduced.

The fashion for black and white houses where the timbers were painted with tar or a thick black gloss paint, for example, was generally a nineteenth-century conceit. It often encourages the decay of timbers by preventing evaporation of moisture from the surface. Where this is causing a problem externally, it may be appropriate to remove the coating using paint strippers and poultices in accordance with the manufacturer’s instructions. Never sand timbers as this will destroy the surface and remove much of their character.

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What to look for: 

Cracked, damaged or decayed infill panels

Suggested action: 

Repair small cracks or areas of damage with appropriate materials. Seek advice from a conservation architect or surveyor if the damage is more extensive.

It is essential that timber-framed buildings are allowed to breathe as this helps to control moisture. This applies as much to the infill panels as it does to the timber framing itself.

In Wales, timber framing was traditionally treated in a number of different ways. On houses, a common method was to infill the gaps between the framing with lightweight panels. These panels could be constructed of wattle and daub, which consists of sprung stakes or staves, often of riven (split) oak, interwoven with riven oak or hazel sticks to produce a structure onto which the daub was applied. The daub could include a mixture of materials, but consisted principally of clay with cow dung, chopped straw or coarse animal hair added to help bind it together and to control shrinkage. Later, nailed riven laths were used to replace the wattle. The wattle and daub or laths were generally plastered internally and rendered externally with a lime mortar. The infill panels would then be limewashed for added protection. Both types of infill are well suited to timber framing as they are flexible and cracks can easily be repaired using a mixture of lime putty and hair.

Other problems with this type of infill panel include loss of key, where the daub, plaster or render become detached from the wattle or laths, and decay of the underlying material itself, usually as a result of beetle infestation. It is often possible to remedy these problems without the need to replace the infill panels.

Brick was also used as an infill material, sometimes as a later replacement. It can be more difficult to maintain a weathertight joint between the panel and timber frame, so look for cracks in this area. Fill small cracks with lime mortar Brick is also much heavier than the other infill materials, so check for signs of stress or movement in the framing.

Seek advice from a conservation architect or surveyor on badly damaged infill panels and problems with the timber framing.

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What to look for: 

Cracked or damaged render covering timber framing

Suggested action: 

Repair small cracks or areas of damage with lime mortar. Seek advice from an architect or surveyor if the damage is more extensive.

During the eighteenth century, exposed timber framing became unfashionable, and the walls and framing were often completely covered over with lime render. The render was often ‘scribed,’ or lined out with mock joints, to look like high-quality dressed stonework.

Cracked or damaged render can allow moisture to penetrate and lead to problems with damp, so it should be repaired promptly. Use matching mortar to repair small areas, but be sure to reinstate any scribing on the wall surface.

If there is extensive damage or failure of the render, take advice from a surveyor or architect.

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What to look for: 

Decayed or loose weatherboarding

Suggested action: 

Refix loose weatherboarding using non-ferrous nails. Cut out damaged or decayed sections and replace with suitable new boards.

Weatherboarding was a traditional way of cladding timber-framed buildings in some parts of Wales. It was frequently used on agricultural buildings and is particularly common in Radnorshire and Montgomeryshire. The boards are generally slightly tapered and fixed horizontally to the framing with the thicker end overlapping the board below by 1 inch (25mm) or so. Early boards were of split oak or elm of varying widths, and were generally left to weather naturally.

From the eighteenth century onwards, weatherboarding was usually made of imported softwood. Logs were sawn into thick planks, then sawn again to give two thinner bevelled ‘feather-edged’ boards. As a result, the direction of the grain varies, making the boards susceptible to splitting and warping. Softwood also tends to be less durable than hardwood and boards were therefore treated with tar to preserve them.

Shiplap boarding is a late nineteenth century innovation that is not appropriate for use on an historic building.

Use stainless steel or galvanized nails to refix loose weatherboards. If a board has decayed or split, cut out the affected section and replace with a board of the same dimensions and timber variety if possible. Do not substitute softwood for hardwood boards. Finish the new timber with the same surface treatment as the original board.

What to look for: 

Damp, disintegrating or damaged walls

Suggested action: 

Check for signs of dampness or vermin damage. Consult a conservation architect or surveyor before undertaking any repairs.

Clom is an unbaked mixture of subsoil containing clay with other materials, such as straw or coarse animal hair, that act as binders and control shrinkage. Clom-walled buildings were once widespread throughout Wales, but are now only found in numbers in Carmarthenshire and Ceredigion.

Clom is not a load-bearing material, so it tends to be found mainly on single storey cottages. On larger houses it is used either in conjunction with load-bearing timbers or where the walls are constructed of stone to first floor level. The material is relatively weak and fragile, although the rounding of corners and edges makes them less likely to be knocked off. This gives clom buildings a soft, almost organic appearance, which is important to retain.

A protective coating of limewash is usually applied to clom, and it should be refreshed annually or as required. Impermeable materials, including cement and acrylic paints, must, however, be avoided as they trap moisture within the clom with potentially disastrous results.

 Clom will disintegrate if it is subjected to prolonged damp, so it is vital to ensure that roofs and rainwater disposal systems are well maintained, and the area around the base of walls is properly drained.  Clom is known as cob in south-west England, and there is an old Devon saying: ’All cob needs is a good hat and a good pair of boots’. This is a very useful adage to remember when maintaining any clom building.

Rats can burrow though clom walls, causing considerable damage. If rats are present, eliminate sources of food and shelter and contact your local council for advice on control measures.

Small holes can be patched with new clom, but the material will shrink, making it difficult to achieve a weather-tight join. Larger holes can be repaired using pre-made clom bricks or blocks bedded in a weak lime mortar and pinned together with non-ferrous supports. It is advisable to seek the advice of a conservation architect or surveyor with experience of clom-walled buildings before undertaking any repairs.

What to look for: 

Flaking or weathered limewash

Suggested action: 

Renew limewash regularly.

Limewash provides a protective coating, which acts as a barrier against penetrating damp. While providing a good weatherproof cover, it also allows any water within the structure to evaporate through the surface.

Limewash should be applied regularly, ideally every year, to be effective.

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What to look for: 

Flaking or blistered paint 

Suggested action: 

Repaint with a silicate microporous paint, or, if an impermeable paint layer is causing deterioration of the wall, investigate removal.

Microporous silicate paints will allow a building to breathe and may be used in situations where limewash may be difficult to apply. Surfaces should be repainted every 3 to 4 years or in accordance with the manufacturer’s recommendations.