St. Peter & St. Paul Barnby Dun - Part 2

A carved detail to an ornate buttress on the chancel

Continuing with my investigation of the church of St. Peter and St. Paul in Barnby Dun, a close look at the Victorian headstops to the chancel shows that they have generally not weathered well, with many being severely blackened. 

Headstops on the south elevation of the chancel

From 1965 to 1994, sulphurous emissions from the nearby Thorpe Marsh power station would have resulted in the formation of an impermeable sulphate skin on the surface of the dolomitic limestone. Particularly in sheltered areas, where these sulphates cannot be removed by rainwater and repeated recrystallisation occurs, this often leads to cavernous decay. 

Headstops on the east elevation of the chancel

Although the dolomitic limestone of the Cadeby Formation contains a very high proportion of the mineral dolomite, which in its pure form is quite resistant to acid attack, this varies considerably within the formation and weathering resistance of buildings made from them will reflect this. 

Headstops on the south elevation of the chancel

As mentioned in my previous post, Victorian architects often specified Jurassic oolitic limestone for restoration – perhaps in response to the deterioration of the Anston stone at the Palace of Westminster – and it is possible that this could account for the rapid deterioration of the Victorian headstops on the chancel. 

A general view of the chancel

Subtle variations in colour between the mediaeval and Victorian masonry, with a slight yellowish tinge in the latter being noticeable to my eye, is often a good indication that the stone is supplied from more than one quarry source or from different beds within  the same quarry. 

The west end of the south elevation of the chancel

At Cadeby Quarry, for example, which is one of the very few suppliers of Permian dolomitic limestone in the UK, thirteen separate beds have been identified, all of which will have slight variations in grain size, crystallinity, porosity and oolite, shell and dolomite content. 

A Decorated Gothic style window in the chancel

All of these factors can affect the durability of Magnesian Limestone in normal atmospheric conditions. Other quarries, lying above the Yellow Sands Formation, produce limestone that contains higher proportions of sand and iron oxide, which can also affect the weathering properties of the stone. 

Gargoyles on the south aisle

The mediaeval gargoyles and the crocketed and sculpted buttresses, which were probably left in place or recycled during the rebuilding of the chancel, are all highly weathered but none show the deep cavernous decay seen in the headstops. Furthermore, the limestone from which they are carved is very pale in colour, with a light grey patina. 

An ornate buttress on the chancel

Looking closely at the plain masonry to the south elevation of the chancel, most of the blocks are deeply weathered, with the softer beds scoured, and this suggests that the Victorian rebuilding left most of the mediaeval masonry intact. 

A buttess repaired with stone slips

Apart from the windows, I didn’t note any areas of extensively restored masonry but, in a few places, the SPAB method of ‘honest repair’ with stone slips has been used and, unfortunately, several very poor in situ repairs have been carried out with an inappropriate mortar. 

The south door of the chancel

The variable durability of dolomitic limestone, and susceptibility to all masonry by rising damp and crystallisation of salts in the groundwater, is illustrated in the south door of the chancel. The lower two sections of the jambs have been renewed very recently and, in the absence of a damp proof course, the left section in contact with the ground is already decayed.

Deterioration of the stone to the chancel door jamb

On the south elevation, apart from the south door to the chancel and the porch, the various Decorated Gothic windows mirror those on the north elevation; however, the masonry to the walling comprises blocks that are of a very irregular size and shape, which contrasts with the very regular blocks used in the rest of the church.

A general view of the south aisle and clerestory