A Stone Matching Exercise - Part 2

Samples from Aldershot Town Hall

A couple of days after I had spoken to my brother at Triton Building Restoration about the sandstone used at Aldershot Town Hall, I received a couple of small pieces from the plinth through the post.

Samples when dry

Looking at them on my hand, they appear very distinctly grey in colour are considerably darker when wet. They are both very fine grained and the larger piece can be strongly rubbed with the fingers without any friable material being dislodged. 

Samples when wet

The smaller piece has distinct fine laminations, which form planes of weakness that have been exposed as angular surfaces with small patches of a distinctly green mineral, and the weathered surface has a light brown patina.

An examination with a hand lens

An examination with a hand lens reveals well sorted angular quartz grains and very occasional tiny flakes of mica, with no obvious oxidising iron minerals or degrading feldspar in the matrix, as is common in the Carboniferous sandstones.

A negative test with hydrochloric acid

Small black grains, which are too small to identify, are scattered throughout the stone and a very pale green tinge can often be seen, with occasional concentrations that are obviously green. There is no reaction to a test with dilute hydrochloric acid.

The Triton Stone Library

I no longer have the large collection of building and decorative stones, which formed the basis of the Triton Stone Library that I designed back in 1997, but I can’t recall having seen a sandstone like this before or suggest a good match for repairs.

Various reference books

It would need petrographic analysis to provide further information on the samples, but I don’t have a petrological microscope and it is extremely unlikely that an organisation like the British Geological Survey would be paid to undertake this for a Grade II Listed building.

Various tools and specimens