Know your building
Your chapel will have changed over time as fashions have changed or to meet the needs of growing congregations. Understanding how these different phases in a building’s development can help to explain why problems might occur, such as cracking at the joint between old and new parts of a building.
Understanding the materials used and how they work is also important as it can prevent costly mistakes from being made. For example, repointing soft stone or brickwork using a hard cement mortar, rather that a soft lime mix will trap moisture within the stone or brick, rapidly accelerating the process of decay. Lime mortars and renders are intended to be sacrificial by being softer than the basic building material. They help a building to breathe and to tolerate a degree of movement, but they will need to be repaired or replaced periodically. Nevertheless, it is far easier to repoint a wall than it is to rebuild it once the stone or brick has lost structural strength.
What causes decay?
Understanding problems correctly can save a considerable amount of money and prevent unnecessary damage or loss of historic fabric. Before undertaking any repair it is essential that the underlying cause of the problem is properly understood and addressed. It is pointless, for example, treating an outbreak of dry rot if the damp penetration that has caused it is not tackled. The environmental conditions that the fungus needs to survive will continue and further outbreaks are likely to occur. Similarly, there is no need to treat timbers against beetle infestation if the damage occurred long ago and the infestation is no longer active.
The main purpose of maintenance and repair is to restrain the processes of decay without damaging the character of a building. Repairs should be kept to the minimum required to conserve the building without unnecessarily disturbing or destroying the historic fabric.
Use tried and trusted materials and techniques
The use of inappropriate modern materials in traditionally constructed buildings can cause more serious problems than they are intended to solve. Repairs should generally be carried out on a like-for-like basis using materials and techniques that match those originally used. This will help to ensure that the old and new are compatible in terms of their performance and appearance. The only exception is where there is a fundamental design fault. For example, the valley gutters of historic buildings are often lined with pieces of lead that are too long to comply with current building practices. Lead is subject to thermal movement, and in overly long pieces this can lead to tears that will allow water to penetrate the roof.
Further information can be found on Cadws Maintenance Matters Wales Website