Andy Sutton and Daniel Black, Pete Walker, University of Bath - PDF document

Andy Sutton and Daniel Black, Pete Walker, University of Bath UNFIRED CLAY MASONRYAn introduction to low-impact building materials INFORMATION PAPER IP 16/11This Information Paper provides a broad view of the benefits and limitations of non-loadbearing unfired clay brick or block for those considering its use in construction projects. Compared with many alternative products, unfired clay masonry is a low-impact building material, and has one of the longest histories of traditional unfired clay block (‘clay lump’) buildings are However, such thin walls of unfired clay are best suited bonded with clay- or lime-based mortar. Recent work P16-11.indd 1 03/11/2011 16:37:47 2 UNFIRED CLAY MASONRY – IP 16/11moulds or, more commonly, by extrusion (Figure 3). Some (green) bricks, and it is their use of fired brick-extrusion as resistant to damage as fired clay, hence care should be are kept dry, including protection from rising moisture from the ground or very high humidity levels (Figure 4).design stage (Figure 5). Most notably, protection from high Usually, unfired clay should be used protected from excess moisture and sited above the damp-proof course/damp-proof membrane level. If protected from direct wetting, unfired clay materials can be used in internal (Figure 6). It is advisable to bed unfired clay bricks or (or other similar water-resistant material) to avoid damage in case of accidental flooding. In other respects, unfired also provide sufficient strength for normal-duty fixings, such as plumbing, electrics and shelves. As with aircrete, breaking, to make a custom fit. Off-cuts from construction mortar, thereby minimising waste considerably.Unfired clay notably differs from aircrete in its stability. Typically, this issue can be resolved with thicker walls than traditional uses of earth building.and improves strength and durability. Traditionally, the Figure 2: Figure 3: Extrusion of clay bricks using conventional brick- Figure 4: P16-11.indd 2 03/11/2011 16:37:54 3 UNFIRED CLAY MASONRY – IP 16/11use of straw reduces shrinkage cracking, and the use of resistance and fixing capacity. Since the early twentieth century, cement has commonly been used as a soil stabiliser in civil works as well as earth building, most of using a high-energy binder. Some earth builders feel that cement-stabilised clay should be regarded as ‘poor concrete’, rather than earth. Historically, lime has also brick to those beneath. Traditionally a clay or lime mortar was used. However, for thin (105 mm) green brick walls, dewatering of the mortar, although overwetting the bricks practice not to apply top-coat internal finishes until the (Figure 7). More commonly, it will be rendered and painted. In this case, vapour-permeable renders or plasters, such as lime or clay, should be used to allow the unfired clay. Both lime and clay finishes retain the Importantly, the vapour-permeable performance of the building owners appropriately advised. Vapour-permeable of moisture, such as from a leaking roof, may facilitate mould growth and surface blistering. However, treatment the transfer of vapour. FURTHER READING AND SOURCES OF INFORMATION BRE and University of Bath. Low-impact materials: case studies. Unfired clay brick: the WISE building. Available at: www.bre.co.uk/page.jsp?id=2669. Devon Earth Building Association (DEBA). Further reading list. Available at: www.devonearthbuilding.com/reading_list.htm. East Anglian Regional Telluric Houses Association (EARTHA). Downloads and technical papers. Wymondham, EARTHA, 2011. Available at: www.eartha.org.uk/downloads.html. Jaquin P. How mud bricks work. Proceedings of the EWB-UK National Research Conference 2010 (‘From small steps to giant leaps ... putting research into practice’), Cambridge, 19 February 2010. Available at: www.hedon.info/docs/EWB_HABITAT_Paul_Jaquin_How_Mud_Bricks_Work.pdf. Jaquin P. Humidity regulation in earth buildings. London, Ramboll Technical Forum, 2009. Available at: www.historicrammedearth.co.uk/Humidity%20regualation%20in%20earth%20buildings.pdf. sustainable architecture. Basel, Birkhäuser, 2006.Morton T. Earth masonry: design and construction guidelines. Trotman P. Earth, clay and chalk walls: inspection and repair Weismann A and Bryce K. Building with cob: a step-by-step guide. Totnes, Green Books, 2006.Weismann A and Bryce K. Using natural finishes: lime and clay based plasters, renders and paints. Totnes, Green Books, 2008.Woolley T, Kimmins S, Harrison P and Harrison R. The green * All URLs accessed October 2011. The publisher accepts no Why specify unfired clay brick and block? Familiar form of construction Low-carbon form of masonry Vapour-permeable wall construction finishes can be applied Use limited to above damp-proof course or equivalent Very low U-values will require thicker walls than some P16-11.indd 3 03/11/2011 16:37:57 4 UNFIRED CLAY MASONRY – IP 16/11 Typically a lime or clay mortar structural engineer’s design Above 2.4 m the wall slenderness and stability should be reviewed Fired brick (or other water-and to raise the non-water- Figure 5: Figure 6: Figure 7: Unfired clay brick walling at Neal’s Yard, Dorset(Courtesy of Feilden Clegg Bradley Studios) Typical properties of unfired clay brick As a natural product, performance can vary slightly, but 3 2 P16-11.indd 4 03/11/2011 16:37:57 5 UNFIRED CLAY MASONRY – IP 16/11 What is BRE Connect Online? – the UK’s leading centre of excellence on the built environment. BRE from IHS BRE Press giving nd out more 650 books, reports and guides – research, innovation, The Green Guide to SpeciÞ ng – authoritative state-of-the-art reviews – BRE research and how practical guides to good building and repair work and much more... What’s new in 2011? More than 50 new titles, Airtightness in commercial Design of durable concrete structures Environmental impact of floor Low-water-use fittings Ventilation for healthy P16-11.indd 5 03/11/2011 16:37:59 6 UNFIRED CLAY MASONRY – IP 16/11 is the UK’s leading centre of expertise on the built environment, research, consultancy, training, testing and certification organisation, and beyond. The BRE Group is wholly owned by the BRE Trust, a the benefit of all. All BRE Group profits are passed to the BRE Trust to on all aspects of the built environment. We make every effort to it is published. However, we can take no responsibility for the BRE, Garston, Watford WD25 9XXTel: 01923 664000, Email: enquiries@bre.co.uk, www.bre.co.ukInformation PapersDigests, Information Papers, Good Building Guides and Good Repair BRE Connect. For more details call 01344 328038. are available from www.brebookshop.com, orIHS BRE Press, Willoughby Road, Bracknell RG12 8FBTel: 01344 328038; Fax: 01344 328005; Email: brepress@ihs.comWatford WD25 9XXTel: 01923 664761 www.brebookshop.com The preparation and publication of this Information Paper was funded by BRE Trust.The authors also wish to thank Adam Weismann (Clayworks) and Pat Borer (CAT) for their expert input in the production of this Information Paper. LOW-IMPACT BUILDING MATERIALS SERIES Cross-laminated timber (IP 17/11) This series of Information Papers provides a comprehensive yet accessible introduction to various low-impact building materials. The information limitations and typical properties of the various materials. To complement these Information Papers, a series of five case studies has also been produced brepress@ihs.com, +44 (0)1344 328038, www.brebookshop.com.The case studies can be viewed online at www.bre.co.uk/page.jsp?id=2669. P16-11.indd 6 03/11/2011 16:37:59