St John


The interior walls of the church and the majority of the reredos, with the exception of the carved figures in the niches, appear to be constructed from local magnesian limestone, and are affected by salt efflorescence and in some areas exhibit decay well beyond their age.

The short and intermittent periods of heating within the church, and the resulting fluctuating temperatures, cause changes to the relative humidity of the enclosed air. When the heating is switched off, the subsequent drop in temperature causes the excess moisture to condense on the cooler stone, activating the magnesium salts inherently present in the stone. As the stone then dries out these salts crystallise and further damage the stone, as can be observed on many of the walls. The crystals, which can be seen, are of magnesium sulphate - ie Epsom salts, though you are not advised to use them for medication!

A portion of the House of Lords, the Perlethorpe Church and Thoresby Hall are built of a similar stone. The external walls are made from the possibly purer calcium oolitic limestone and do not show the same symptomatic decay.

With the exception of the bell tower the interior of the church is pointed in lime, helping the walls to breathe. The exterior walls are almost entirely cement pointed, which can, owing to its impervious nature, cause the wall to retain water, although with the tight ashlar joints, no major decay is visible on the stonework adjacent to the joints.