I was responsible for all stone cleaning from ground level to just below the pinnacles on this huge project which is

described very well here and here.


Fig 1. Chapterhouse pre-cleaning (left) and post (right) (photos: stowandbeale.com)

A range of cleaning techniques was used to accommodate the different soil types found on the building. At high level

and on undercut, sheltered surfaces throughout the building especially those facing westwards, thick sulphation crusts

were found which were difficult to remove. Organic growth was present on all surfaces especially at high level where

the porous stone allowed the growth of carpets of moss.


The cleaning techniques used were:

1. Thick sulphation crusts on decorative areas were carefully chiseled off to within a few mm of the stone surface. The

remaining sulphation was abraded away using a Dremel handtool with a tungsten carbide routing bit. Ammonium

carbonate poultices, further Dremel, hand brushing (stainless steel lambchop/stainless steel toothbrush) and a small high

pressure steam lance were used in rotation to produce an acceptable level of clean stone.


2. Thick mossy growth lifted with wooden tool and stone cleaned with high pressure steam (Doff)


3. Ashlar areas and buttresses were first treated with high pressure steam (Doff) to remove organic soiling,

followed by timed nebular water sprays to lightly sulphated areas and treated to subsequent Ammonium Carbonate poultices

where sulphation and soot build up was denser.


4. Areas sensitive to water penetration such as the large tracery windows were first scrubbed with stainless steel lambchop

brushes and washed down using hand-held water sprays. Ammonium carbonate poultices were used on areas of stubborn

sulphation mostly found in sheltered areas.



The cleaning of the Westminster Chapterhouse to the standard required, where no stone was lost or surface damaged

showed that a complex interplay between different techniques is necessary to achieve a satisfactory end, to avoid

either over, or indeed, under cleaning.