BCD 2019

PROTECTION & REMEDIAL TREATMENT 4.1 133 C AT H E D R A L C O MM U N I C AT I O N S T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 1 9 degree of cleaning may be a matter of negotiation, but the final decision is most often guided by the test panels. It is usually much more important to achieve an even result rather than the brightest clean, and understanding the degree to which this is possible is often only determined during the trials. Leaving it up to the cleaning contractor or operative to determine the appropriate level of clean is rather like expecting a painter or decorator themselves to choose a paint scheme. Do not be surprised if their choice is not what was wished for. Further Information British Standard BS8221-1:2012 Code of practice for cleaning and surface repair of buildings – Part 1: Cleaning of natural stone, brick, terracotta and concrete, 2012 English Heritage, Practical Building Conservation: Stone , Ashgate, Farnham, 2012 English Heritage, Practical Building Conservation: Concrete , Ashgate, Farnham, 2012 J Fairchild, ‘Abrasive Cleaning Methods for Masonry’, Building Conservation Directory 2016 Siegfried and Snethlage, Stone in Architecture , Springer, Verlag-Heidelberg-Berlin, 2011 Archive of cleaning articles: www.buildingconservation.com/articles/ articles.htm#cleaning JAMIE FAIRCHILD is a former materials engineer in the quarry industry with over 25 years of experience in masonry cleaning and is a director of Restorative Techniques Limited. He provides training and consultancy including tuition for masonry cleaning and other master classes at West Dean College. reagents, tools and equipment used and, most importantly, a familiarity and empathy with the substrate. Preference is given to those methods least likely to generate salts or retain residues. For building façades, a reasonable ambition is that the method does not remove sound surface visible to the eye. Throughout the cleaning works ensure good communication, supervision and recording – inspect the work regularly. Formalise the acceptability of each stage of the work. TRIAL CLEANING The most important tool for the evaluation of cleaning methods is to undertake trials. These are normally carried out at two stages. Pre contract trials should be undertaken at the earliest opportunity, well before the main works and in discreet locations representative of the substrate, soiling and detail. The aim is to demonstrate the suitability (or not) of each method and to determine the speed and cost of the operation. All of the key decision makers (client, architect/surveyor, conservation officer and others) should be present during the trials so that the options are understood, acceptable parameters demonstrated and exemplar panels agreed. It is important to record and disseminate the pertinent test information for each panel, including before and after photographs, the location, ambient conditions and operating parameters selected. Contract trials aim to demonstrate the ability of the contractor to replicate the exemplar panels using additional test panel locations. Acceptable panels should be witnessed by the client’s representative and formally adopted as control panels for the duration of the cleaning work. It is important that the cleaning operative is briefed beforehand as to suitable locations for test panels and the level of cleaning Test cleaning of a limestone pediment to remove mastic and algae using a superheated water system: left, after 30 mins (Photo: Restorative Techniques Ltd), and right, after four weeks (Photo: Anthony Joubert SLP). Sufficient time must elapse before the success or failure of the cleaning method can be correctly determined. A test panel showing the effects of using the latex method for the removal of soot following fire-damage (Photo: Restorative Techniques Ltd) anticipated by the interested parties. Locations are sometimes chosen deliberately to target masonry which is due to be replaced or covered up, but it is important that the test areas are representative of those being retained. The size and location of the test panels should be indicated on a plan or photograph or directly on the substrate with temporary marker (crayon, chalk or tape) and a unique letter or number retained beside each. In the case of a listed building the final arbiter is likely to be a conservation officer and so it is most important to understand their wishes and expectations. The acceptable