THE CHURCH OF ST. LAWRENCE
Exterior
The main walls of the Church consist of flint with clunch dressings, some brickwork, tilehanging and rendering. Very few of the flints to the tower and Nave have been knapped; however great care has been taken with the knapped flints to the Corpus Christi Chapel. There are also some large flints and good examples of Hertfordshire Pudding Stone within the tower walls. All of the stone and rubble walling has been bedded in a lime mortar; in certain places the lime mortar has been repointed with modern cement based mortar.
The stone and flints have been used in a simple chequer pattern in the walls of the South East Chapel; elsewhere the walls are predominantly faced with flint and some isolated stone. There is brickwork at the top of the tower and bricks or tiles have used as a replacement for defective stonework. Elsewhere Bath or Portland stone has been used in new openings, alterations to openings and some repairs to chequered walls. The walls to the Nave were originally rendered with Lime mortar; this was removed in the restoration of 1932 although some sections of the North wall and the north and South Aisles still have a rendered finish. Some areas of defective render have been renewed with a modern cement based render and a pebble dashed finish.
Chalk is the most widespread of the Cretaceous Limestones and Clunch is the name given to stone quarried from the compact beds of the Lower Chalk. In practice this term is often loosely applied to all forms of chalk stone. Totternhoe near Dunstable in Bedfordshire is a well known source of Clunch and the quarry still provides stone for building conservation work. Clunch is easy to carve but not very weather resistant; polluted acidic atmospheres pose a very great threat to all limestones. If the stone is allowed to become saturated, frost will also be a very great hazard. Because Clunch weathers so badly it must be protected by skins of lime-wash which need to be applied regularly. This regular application of a thin coat of lime-wash is a very old method of stone preservation; it is particularly effective with limestones and contributes to the long life of the buildings.
Hertfordshire pudding stone is a conglomerate composed of fragments, generally rounded by contact with water, of previously existing rocks, held together by natural cement. Flint is a hard dense, fine grained stone; it is a form of silica, and occurs within chalk. Flints may be broken, known as knapped, and the broken surface used as the exposed finished face. Where panels of knapped flint are used with freestone the result is called flushwork; this is evident in the walls of the Corpus Christi Chapel.