Contemporary Research Paper

The revival in the use of hot-mixed lime mortars has been gathering pace across the UK and Ireland over the past three years, and the use of quicklimes in conservation and repair is now becoming increasingly routine. This has injected new energy and insight into the wider lime revival, affecting not just construction mortars but also decorative finishes and surface treatments.

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Contemporary Research Paper

The "Hot Mixed Mortars Revival" has been the collective effort of Irish, Scots and English masons and conservation professionals and has reenergized the lime movement across the British Isles. This paper seeks to provide a narrative for this, as well as to summarise the essential benefits of hot mixed lime mortars for use in the compatible repair and conservation of old and historic buildings across the world.

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Contemporary Research Paper

A hot-mixed lime mortar is prepared using quicklime. Typically this involves a "dry slake", during which the quicklime is mixed with naturally moist or slightly moistened aggregate (sand, stone dust or subsoil). In the case of sand or stone-dust mortars, this initial dry slake is followed by the addition of water sufficient to produce a workable mortar for immediate or later use.

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Contemporary Research Paper

Most lime mortars, for most uses, for most of history, were hot-mixed using quicklime. Lime mortars commonly used today, for conservation and repair, or for new build, tend to be Natural Hydraulic Lime-based or designed ‘products’, less often putty lime mortars. This seems anomalous and confounds our general inclination towards like-for-like, compatible repair using authentic materials – as well as the requirement of BS7913 (1998).

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Contemporary Research Paper

The last five years or so have seen a revival in use of hot-mixed mortar. While many people have welcomed this as a way of making more authentic mortars for conservation, others are sceptical or even hostile to what they see as a new fad. Before exploring the pros and cons of hot-mixed mortars, it is worth reflecting on the past 40 years of lime use and how we have arrived at the current situation.

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Book (Introduction)

Traditional mortars are eminently workable, effectively porous, economic in use and appropriately durable. Used in buildings for thousands of years, these materials are ideal for repair and conservation work. Unlike cement or modern hydraulic lime, their routine use would make a significant contribution in the struggle against climate change. However, despite the 1975 'lime revival' there remains a deficit in research into the most-used traditional mortars. This book seeks to redress the balance.

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Lime mortars have been used in buildings for thousands of years and continue to be used for the repair and maintenance of traditional buildings. Most lime mortars currently used in Scotland are based on Natural Hydraulic Limes (NHLs) which are sold in bags as a dry hydrate powder. These products have only been commercially available relatively recently. Prior to the introduction of dry hydrate powdered lime, lime mortars were prepared using either lime putty or quicklime mixes, the latter made as a "hot-mix". These traditional methods of preparing a lime mortar can still be used in building and repair work today.

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For over 1,000 years, hot-mix lime mortar was used extensively in the building of the masonry heritage of Ireland. To repair these structures following the accepted principle of conservation, "like for like", we must seriously consider how we can create more closely matched mortars than those we have been using to date. We have indigenous, commercially available quicklime, so a practical solution would be to use this in combination with imported natural hydraulic limes and/or pozzolans, as required.

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The most commonly found historic mortar proportion encountered in fat and feebly hydraulic lime mortars is 2 lime: 3 aggregate. This was achieved by hotmixing 1 quicklime: 3 aggregate. Successful mixes might also be 1:2 or 1:4. Historic mixes of 1:3 are rarely, if ever, found before the 20thC, when cementgauged slaked lime mixes were typically 1 binder:3, eg 1:2:9. The additional strength of the cement compensated for the loss of lime Though a 1:2:9 mix was typically weaker and less tenacious than a traditional lime mortar mix, it gained an initial set quickly. Historically, hydraulic lime mortars were mixed from quicklime at 1:2 or 1:1, being mainly used underwater and underground.

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Periodical (Turkey)

Nigel Copsey began working with stone as a drystone waller in Cornwall (UK). He trained as a stonemason and carver at Weymouth College in Dorset, becoming established as a lettercutter and stonemason working mainly in the field of stone and building conservation. Based originally in the South-West, the company has carried out projects across England and more recently in Vermont and Andalucia. Nigel Copsey is a fully accredited member of the United Kingdom Institute of Conservation. He subscribes broadly to the principles of the Society for the Protection of Ancient Buildings (SPAB) and to the ideals of its founder, William Morris. He aspires to a thoroughgoing and articulate day to day ethical practice in accordance with international conservation treaties.

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Anglican Cathedral Church of the Redeemer: Link

Bank Slag: Link

Bank Top Kilns: Link

Beverley Gate: Link

Clay Mortar from Normandy: Link

Esk Valley Mine: Link

Rosedale East Iron Kilns: Link

Stonehouse: Link

The Guild Hall York: Link

The Roman Kiln: Link

Vindolanda Roman Fort: Link

Warren Moor Mine: Link

Wayne County Courthouse: Link

York House: Link

York Minster: Link

Field Prepared Mortar Performance Test Notes: Link

What is NHL? Does it Have a Role in Conservation?: Link

DIBDIN Mortar Strengths: Link

Hot Mixed Lime Mortars: Link

Hot Mix Economics: Link

Lime Revival: Link

The Problem with NHLs: Link

Hot Lime Harling: Link

Plastering: Link

Lime and Building Patterns: Link

Bond of Mortar to Masonry Units: Link

The New Practical Builder and Workman's Companion: Link

Mud Mortar: Link

Practical and Theroretical Manual on Lime Burning: Link

Rudimentary Treatise on Limes, Cements, Mortars, Concretes, Mastics and Plastering: Link

New Pratical Encyclopedia of Building and of Habitation: Link

Rural School of Architecture: Link

Durability of Mortar and Masonry: Link

A Treatise on Building in Water: Link

The Rudiments of Practical Bricklaying: Link

Gillmore on Hydraulic Lime Production in France: Link

Construction of the Edystone Lighthouse with Stone: Link

London Prices of Bricklayers’ Materials and Works Both of New Buildings and Repairs: Link

Handbook on Masonry Design and Construction: Link

Malton Estate Agent's Memorandum Book: Link

The Rural Economy of Yorkshire: Link

The Art of the Mason: Link

Lime, Hydraulic Cement, Mortar and Concrete: Link

Theoretical and Practical Treatise on the Art of Building: Link

Limestone and its Products, Their Nature, Production and Uses: Link

The Cyclopedia or Universal Dictionary of Arts, Sciences and Literature: Link

Strength Considerations in Mortar and Masonry: Link

Treussart Petot and Courtois on Mortars: Link

Lime and Cement: Link

Masons and Builders Guide: Link

The Importance of the Slake: Link

Preparation and Use of Mud Mortar in Masonry: Link

Mud Mortars in Masonry Construction: Link

Earth Mortars and Earth Building as Referenced in Old Texts: Link

Lime Plastering: Link

Essays on Hydraulic and Common Mortars and on Lime Burning: Link

Plastering in the UK and Europe: Link

Earth Plastering Analysis and Specification for Conservation Repair and Restoration Works in Malton: Link

Lime Archives: Link

Practical Treatise on Limes Hydraulic Cements and Mortars: Link

Theoretical and Practical Treatise of the Art of Calcining Limestone and Mortars: Link

Lime Consensus Within Old Texts: Link

Cyclopedia of Practical Husbandry Rural Affairs in General: Link

Malton 1593 Terrier Transcription: Link

New Pratical Encyclopedia of Building and of Habitation: Link

Mud Vitruvius: Link

Building Manual of Masons: Link

Hot Lime Mortars: Link

Winter Working: Link

Materials of Construction: Link

Mortars That Are Used in the Construction of Civil and Hydraulic Works: Link

The Complete Works of Gaius Plinius Secundus Delphi: Link

De Agricultura: Link

Cyclopedia of Bricklaying Stone Masonry Concretes Stuccos and Plasters: Link

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Contact Details

Hot Mixed Mortars
Hall Farmhouse
North Yorkshire
England, UK
YO18 7SA

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