Your church walls, like the roof, must act as an efficient barrier against the elements and they need the same regular inspection and attention to good maintenance. They also work to support the full weight of the roof (unless the building is of framed construction) while enclosing and defining the inside space and providing security and privacy.
Before the mid-19th Century, when transport became easier and cheaper, they will generally have been built from the most suitable locally available material. If your church was built before the 1930s it will most likely be walled in stone or, unusually in Scotland, in brick, which is more often found in ancillary halls and other additions and extensions. From the 1940s, however, modern methods of construction in e.g. concrete and steel were often adopted for a new wave of church building, particularly in the New Towns and expanding suburbs, resulting in some different technical demands on their maintenance and repair.
Where a rendering has been applied it is usually to give added weather protection to exposed or less finely-built areas of masonry or to unify the appearance of a building which has a variety of surface finishes.
Brick walls may be solid or built with a cavity inside, separating the external and internal skins, as protection from moisture transmission and to improve insulation. Cavity walls can be distinguished from solid walls by the difference in bonding.
In stone and brick building the mortar joints bonding the masonry together were traditionally formed in the tried and tested mixture of slaked lime, sand and water. Portland cement has widely and mistakenly been used to replace the lime content in much stone repair work since the 1930's with the consequences explained below.
The STONE mainly used in Scottish building was formed in one of two basic ways:
1) SEDIMENTARY comprising:
a) Sandstone which is made up of small particles of rock deposited in beds or layers and compressed over enormous lengths of time into solid form, its hardness depending on the degree of pressure and material composition.
2) IGNEOUS and METAMORPHIC, the result of volcanic activity, typically forming
a) Granite. This extremely hard and durable stone has been quarried particularly around Aberdeen and in parts of Dumfries-shire and Galloway. Nearly all our granite church buildings can be found in these two areas.
b) Whinstone, a dark-coloured material found mainly in Lanarkshire and the Borders, is a particularly hard and durable type of stone which does not readily fracture and spall.
c) Schist is a coarse-grained form of metamorphic rock found, for example, in the West Highlands, where churchbuilders have often used this easily-split material. It is unsuited for dressings and other carved stonework where it has normally been replaced by sandstone.
Limestone, another sedimentary type, has been little-used in Scotland as building stone and has mainly been exploited for its use as lime in mortars and harling and for agricultural purposes.
Scotland's extensive deposits of SANDSTONE have ensured its constant use in church building and repair until, by the 1930's, nearly all the quarries were exhausted or had became uneconomic for other reasons. Except for surviving sources mostly in Dumfriesshire (red sandstone) and in Moray (light buff), our sandstone is now supplied mainly from the north of England.
Blocks have traditionally been finished in a variety of ways depending on the quality of the stone and the available resources in money and skilled labour. They range from fine ashlar with almost invisible joints to coarse rubble fieldstone built uncoursed with small pinnings and with wider mortar joints.
see Roofs and Roof Drainage
Stone walls will normally have been built with fair faces to the outside and inside and with a rubble core in the centre.
The way the stone is laid is vitally important to its durability. Its original formation can be seen in the visible layering of each block and they should be laid in the same way with the 'strata' running horizontally across the stone.
When, by mistake, a block is laid with the layers running vertically from the front surface to the back or (worse) from side to side across the width, it will eventually split or flake away, sometimes helped by frost action. Such damage should not cause huge structural problems in a wall but it will be unsightly and can cause nearby stonework to decay due to extra pressure and water finding its way to the inner part of the wall.
When descaling such stonework use wooden tools and a stiff bristle brush, remembering to sweep up the debris.
If stone mullions or tracery have been affected in this way, more urgent repair will be called for to avoid possible major work to the whole window.
A well-trained stonemason will use the repair method best suited to the type of stone and degree of erosion. Where spalling is superficial it may be sufficient to brush back the loose material to a firm surface but if the problem goes deeper, indenting of matching replacement stone will be recommended. For durable repair of small detail, a plastic mortar composition including crushed stone or sand may be preferred but this should only be considered if specially mixed and applied by an experienced mason. Alternative, off-the-peg synthetic plastic compounds cannot be recommended. They will not be matched to the composition of the stone, can trap water in the same way as hard mortars and will have a short life when compared with other methods.
A sandstone wall effectively acts like a sponge, absorbing water that soaks into it and then allowing it to dry out naturally when the weather improves. Drying will of course take place more quickly where walls are exposed to sun and prevailing wind, with north-facing walls being prone to more continuous dampness. The thickness of the wall will normally cope perfectly well with this weathering cycle, often helped by the middle layer of looser stone which allows any excessive incoming moisture to drain away downwards.
Problems can occur, however, at the weakest points which are usually the mortar joints. Poorly maintained or made using hard mortar instead of a rich lime mortar, they will allow water to be drawn into otherwise sound walls and this can be especially severe when affected by driving rain. Cement-rich pointing will also slow down the natural drying of the wall, making it more vulnerable to further dampness and to frost action which has further potential to damage saturated masonry. Particularly vulnerable are the high-level joints at gable copes, chimneys and parapets which are likely to require more frequent repointing.
The building can also be affected by ground moisture rising from the base of the wall. This is prevented in modern construction by building - in a damp-proof barrier slightly above ground level. Older churches, however, may need to rely on natural drying out and there will normally be nothing to worry about if:
1) the drainage around the church is working efficiently,
2) the ground level has not recently changed significantly
3) nothing has been heaped or piled up against the wall which could trap moisture behind.
There may be underbuilding - a low space between the floor of your church and the natural ground which is also intended to keep the floor free from rising damp and found in all but the oldest buildings. It will be ventilated by small horizontal openings near the base of the wall, fitted with grilles to keep out vermin and any debris that might blow in accidentally. It is important to keep these vents in good condition and to check regularly if there is any obstruction to the free flow of air.
When a masonry wall or part of it has been allowed to become thoroughly saturated, any timber close to or supported by it inside the building must be inspected for possible evidence of rot and helped to dry out, as described below. Such walls may be affected externally and internally by fluffy white staining known as efflorescence, caused by salts within the stone or brickwork moving to the surface. It is not harmful and should disappear in time but if thought unsightly it can readily be removed using a dry brush.
When stone is seen to be eroding on an inside wall it may well be due to excessive condensation rather than to moisture from outside. The remedy is to ensure good air circulation and a regular, even temperature and to avoid the use within the church of those types of heater which give off a great deal of water vapour.
Look out also for any cracks in your walls. If any exist, check whether they have been spotted in a previous professional inspection and, if so, whether any action has been recommended and followed up. Should they appear to be new, there may be no immediate cause for concern if they only affect a single block of stone or brick but should new cracking run through several blocks or in a zigzag pattern through mortar jointing this will very probably indicate a more serious problem, due perhaps to subsidence or failure of some structural nature. Similar cracks that suddenly appear in window and door cills and lintols are also suspect, and should always be looked out for in your inspection. You should then promptly seek experienced architectural or engineering advice as to the causes and remedies. Bulging of a wall is also a sign of possible structural trouble and the same advice applies.
In framed buildings the main loads are carried by the framing, with the rest of the wall consisting of non-structural cladding panels.It is normally more urgent to deal with distress in the frame members (concrete, steel or timber) than with defects in the panels which are less important to the stability of the building.
At the foot of the wall it is good practice to have a gravel-filled trench immediately next to the building to enhance protection against rising damp and to help unexpected overflows from pipes and gutters to drain away harmlessly.
For the same reason, hard surfaces such as tarmac paths and parking spaces should preferably be kept free from abutting the building, especially when not well sloped to drain away from the structure. If possible, find out and record the layout of the underground drainage around the building in case it needs attention.
Plants, especially self-seeded trees, should not be allowed to grow against the walls and their root growth can also further damage leaking underground drains. Ivy growth should likewise be discouraged. Its roots can penetrate and break down mortar pointing. Remove it by cutting main stems and letting it die back naturally.
Harl is the traditional lime based rendering, put on like an overcoat to give added protection to less finely-built exposed masonry and/or to unify or accentuate the appearance of a building. One of the most familiar sights in the Scottish countryside is still the small white-harled kirk standing out against a darker landscape. Harl will usually have been applied with good reason and should not be thoughtlessly stripped off purely because the underlying stonework might be thought more attractive. This and other renders must be mixed with a suitably high proportion of lime in order to let the wall 'breathe' moisture in and out. Many mistaken attempts have been made to apply impervious finishes instead, notably cement-rich renders. They will come away in time as water nevertheless finds ways of penetrating behind, often removing a layer of stone in the process.
If good harling has been accidentally damaged, its composition should be analysed and the same mix used in the repair. It is advisable to seek the advice of a knowledgeable professional or masonry contractor before deciding to completely remove and replace poorer work.
If Masonry Paint is needed for redecoration, use only a mineral-based type and think carefully before painting wall surfaces simply for the sake of appearance when they have clearly not originally been intended for such treatment. Only use limewash or distemper as a finish for lime plasterwork.
Never accept without question claims for the effectiveness of proprietary waterproof products, usually transparent silicone-based treatments, promoted as protecting walls against damp for many years to come. If at all effective to begin with, they will not in fact last long and are most unlikely to give value for money. In some cases they can actually make problems worse.
POINTING is the technical term for applying mortar to masonry joints, including stone and brickwork. Mixes using Portland cement may be appropriate for more modern types of brickwork but a lime mortar should generally be used for work on sandstone walls. When a mortar is harder than the stone it will cause the adjoining material to break or peel away and will not adhere properly over time, allowing water to pass through the joints. Since different types of stone vary greatly in hardness, the mortar to be used will differ from one building to another. For lime to set, a hydraulic input is needed. In certain cases this can be achieved by using some cement in conjunction with the lime. Where walls are of soft sandstone,a hydraulic type of lime should be used with sand to make a suitable cement-free mortar.
Where hard mortar has already been used, the only sound long-term remedy is to rake it out and to repoint using a mix of water, lime, sand and small gravel suited to the consistency of the particular stone. In very fine joints the work may be completed by a shallow application of pure lime putty.
The Scottish Lime Centre can advise on suitable mixes. It is, however, important to understand that even NHL5, the most hydraulic lime, requires temperatures well above freezing for several days in order to set properly.
STONECLEANING is not recommended except in very special circumstances as nearly all methods damage the stone in some way. Washing with a bristle brush is sufficient. If the stone is stained and dirty, look for the reason and remove the cause if it is due to poor maintenance.
Biocides may be used to remove algae and moss - again, examine the reason for its presence. Applying a salt solution may also be effective. It is noticeable how such growth is rare in a salty seaside atmosphere.
Lastly, when engaging a masonry contractor to undertake stone repair, make sure that the firm has the necessary skills. If in doubt, ask to look as previous work.The individual or team employed must be able expertly to match in the new work by maintaining joint widths and profiles and by replicating surface finishes. Where the wall has been built, for example, with smaller pinnings between the blocks this should be repeated, using the least amount of mortar necessary.