Introduction Interiors 1 Interiors 2 Churchyards Exteriors
St Finn Barres Cathedral, Cork

Exteriors

Churches of all denominations play a significant role, locally and nationally, in our spiritual, social, educational and community life. They are often the most prominent, ambitious and significant buildings in their locality and their contents are arguably Ireland's most valuable historic archive. Churches are, by definition, public buildings and are cared for by their congregations but they are also the heritage of their communities. They are a unique building type, their form is such that gaining access to certain parts is often difficult, and they have different patterns of use from other buildings.

Most historic churches are constructed in stone - sandstone, limestone, basalt and granite being the most frequently used. The decay of stone is a process which either occurs naturally or is induced by inappropriate intervention. The various repair techniques require the services of a building professional who understands historic buildings and craftsmen who know how to maintain original joint widths, profiles and match original surface treatments. Pointing is not always necessary but when it is it should be done with a mortar which matches the original. Pointing should match the original in colour, materials and composition, not only to maintain structural integrity but also because variations in colour, texture and profile have a dramatic effect on appearance. When a mortar is harder than the wall material, which is often the case when cement is used, the brick or stone will degrade leaving the pointing protruding.

The patina of age demonstrated by the mellow, weathered appearance of an historic church is impossible to reproduce and is often its most attractive feature. The application of external hard cement renders in place of earlier ones of lime mortar alters the appearance and chemistry of the building. Traditional lime-based renders are soft in comparison to cement-based wall coverings which can be dense and impermeable. When rain hits a soft, permeable render it is absorbed for a time but then dries out naturally. Such renders are flexible and will accommodate movement in the wall, whereas a hard render will crack and allow water in. If the water cannot evaporate through the render it will accumulate behind it and may then travel to the interior of the building causing damp inside the church.

The cleaning of church exteriors should only be undertaken under the supervision of a conservation architect. Any method adopted must avoid damaging the external render, brick or stonework. Using high pressure water methods can force moisture into the building through small cracks and cause water penetration to the interior. Often this is not apparent at the time but creates problems years later.

Roofs should be kept free from debris, leaves and build-up of moss. A 'flat' roof should have a slight fall so that water can drain away. It is important to use neither sticky bitumen-coated fabric as a temporary roof repair nor spray-on coating systems on the underside of the roof. These materials make it difficult to trace any further leaks to their source and hinder the re-use of slates. Repairs should be designed to be reversible so that they can be removed or undone without causing further damage.

The following list of Dos and Don'ts provide general guidance on maintaining church exteriors.

A view of the bell tower

DO:

DON'T:

Exterior

Portland cement

mortar sets by chemical reaction, and is hard, brittle and strong under compression. It is generally impervious to water moisture. If a Portland cement mortar is applied to a building built of lime mortar, either as pointing or as a render, problems arise. The inherent subtle inter seasonal flexing of the lime mortared building will cause minute cracking to occur in the hard but brittle Portland cement pointing or render. These cracks, by capillary action, will actively suck in moisture from the surface into the body of the walls from where it cannot escape back out by evaporation. So it travels in through the lime bedding mortar of the walls to evaporate from the inner surface of the wall and into the inside of the building. Hence the problems of surface salts, paint peeling and worse - dry rot. The building cannot 'breathe'. Consequently the result of the invariably well intentioned application of Portland cement to lime mortared buildings is nearly always damaging and the opposite of what was intended.

Lime mortar

(used for the building of the great medieval cathedrals and right up until the invention of Portland cement at the end of the 19th Century) has two cardinal characteristics after it sets: it retains a degree of plasticity and it allows the passage of moisture. The former attribute means that lime mortared buildings minutely expand and contract between summer and winter. The latter attribute allows a cycle of moisture absorption and evaporation to occur on and in from the outer surfaces of lime rendered and pointed walls. The mortar always provides a conduit for the continuous escape of moisture from within the walls of a building.

This article offers general guidance only; for specific advice contact a conservation architect or other relevant specialist.
© Ulster Historic Churches Trust 2004