Why Lime Mortar Matters: In relation to Traditional Buildings and Heritage Surveys
- Ricky Savage
- Jun 24
- 8 min read
On 22–23 June 2026, the RICS Yorkshire & Humber region held a two-day technical event on lime mortar at Fountains Abbey near Ripon, a little under an hour's drive from us here in Scarborough. Led by the conservation specialist Nigel Copsey, the event combined technical lectures with hands-on demonstrations of traditional hot-mixed mortars and limewashes, and carried four hours of formal CPD. It was attended by four local RICS members.
It is the kind of event that matters a great deal in this part of the country, because so much of our local housing stock was never designed to be treated the way modern materials encourage us to treat it.
A fitting setting: Fountains Abbey
The event was held at Fountains Abbey, one of the largest and best-preserved Cistercian monastic ruins in the country. Founded in 1132 by a small community of monks seeking a simpler, more austere way of life, it grew over the following centuries into one of the wealthiest religious houses in England before its closure during the Dissolution of the Monasteries in 1539. The ruins now sit within the Studley Royal estate, with its celebrated Georgian water garden, and the two together were designated a UNESCO World Heritage Site in 1986. It is precisely the kind of place whose survival depends on a proper understanding of traditional materials and the craft skills needed to maintain them, which made it an ideal backdrop for two days of lime.
It was also a real pleasure to be joined by members of the National Trust's specialist crafts team, five of whom took part in the event. Having people in the room who carry out this kind of conservation work on a daily basis, on the very buildings the National Trust cares for, made the two days feel all the more real and grounded in genuine practice rather than theory.
On a personal note, Fountains Abbey is well worth a visit in its own right. It is a fantastic and historic place, with a good amount of parking and excellent facilities, including a very good restaurant. Everyone I met there was warm and welcoming, including the National Trust staff who joined us for the two days, who proved to be genuinely passionate people. I would highly recommend a visit.
Led by Nigel Copsey
The event was in expert hands. Nigel Copsey is one of the country's foremost authorities on traditional lime and earth mortars, with a career in building conservation spanning more than four decades. He began as a dry-stone waller and trained as a stonemason and carver before moving into consultancy, hands-on repair and teaching. He has worked extensively across North Yorkshire since 2001, including writing the mortar guidance for the North York Moors National Park, as well as on historic buildings internationally, from the Irish Hunger Memorial in New York to projects in Canada, Spain and across Europe. He led the practical conservation skills module at the University of York for a decade, holds an MA by Research on the history of mortars, and is the author of Hot Mixed Lime and Traditional Mortars (2019). A long-standing SPAB member and an accredited conservator, he is a leading advocate for the like-for-like use of hot-mixed lime in the repair of old buildings, which made him an ideal person to lead two days of practical instruction.
Old buildings need to be vapour permeable and why lime mortar matters
A great many of the homes we survey across Scarborough and the surrounding towns and villages were built before 1919. These are predominantly solid wall properties, typically a single thickness of brick usually 9-inch thick, or stone with no cavity, and they were constructed using lime mortar rather than the cement-based products that dominate the modern building trade.
This is not an incidental detail. Solid wall buildings manage moisture quite differently from modern cavity-wall construction. Rather than keeping water out entirely, a traditional wall is designed to absorb a degree of moisture and then release it again through evaporation. Lime mortar, lime render and limewash are vapour permeable, letting moisture move freely and escape rather than becoming trapped within the fabric.
Where cement causes harm
Problems arise when a traditionally built wall is repaired or "improved" using modern cement-based mortar, render or pointing. Cement is comparatively impermeable. Applied to a solid wall, it restricts the wall's ability to evaporate moisture, and that moisture has to go somewhere.
The usual results are:
Trapped dampness within the wall, often appearing internally as patches of damp that prove stubbornly resistant to the usual "remedies".
Brick and stone spalling, where the face of the masonry blows or crumbles as trapped moisture freezes and expands during cold weather.
Frost damage concentrated behind hard cement pointing, where water can no longer escape by the route the building was designed to use.
A common and unfortunate scenario is a homeowner who, acting in good faith, has a solid wall repointed in cement or sealed with a modern render, and then finds the damp problems become worse rather than better. The underlying issue is rarely "rising damp" in the sense the term is usually understood. More often, it is a building being prevented from doing what it was built to do.
The right repair is a lime repair
The appropriate approach for a traditional solid wall property is to repair like with like: lime mortar for pointing, lime render where render is needed, and limewash as a vapour permeable finish. These materials work with the building rather than against it. Events such as the Fountains Abbey gathering are valuable precisely because they keep these skills alive and demonstrate, hands-on, how hot-mixed lime mortars and limewashes are correctly prepared and applied.
One important point that came out of the event is that "lime" is not a single material, and advising a client simply to "repoint in lime" is not specific enough. There are several types, ranging from soft non-hydraulic lime (lime putty) through to the natural hydraulic limes, which are graded by strength: NHL 2, NHL 3.5 and NHL 5. The stronger, more hydraulic grades, such as NHL 3.5, set comparatively hard and dense, and on a soft, traditionally built wall, they can behave almost like cement, to the point of being nearly as damaging as cement pointing. The appropriate choice for most traditional buildings is a softer, more vapour permeable mortar, such as a feebly hydraulic or non-hydraulic lime, or a hot-mixed lime of the kind demonstrated at the event, matched to the strength and character of the original masonry. Specifying the wrong grade of lime can reintroduce many of the very problems it was meant to avoid.
It is worth being candid about one further point. Many otherwise competent builders have been trained almost exclusively in modern materials and do not fully understand traditional construction. As a result, homeowners are sometimes given well-meaning but inappropriate advice: to seal, to render in cement, or to inject a chemical damp-proof course where none is needed. We would always encourage owners of older properties to seek advice from contractors with genuine experience of lime and traditional building methods.
Among the most important obligations any RICS member carries is continual professional development, the discipline of keeping one's knowledge and skills current throughout a career rather than resting on what was learned years ago. Events like this are exactly what that commitment means in practice. I attended the event in person, and there is no substitute for seeing traditional hot-mixed lime prepared and applied at first hand. Watching the material gauged, knocked up and worked is a useful corrective to the way lime is often discussed in the abstract. It reinforces just how different it is to handle, and to specify correctly, from the cement-based products most of the trade reaches for by default.
I was particularly taken with the demonstration of making lime putty. This is produced by slaking quicklime in water, a vigorous and strongly exothermic reaction in which the lime gives off considerable heat as it combines with the water. I was genuinely surprised to see just how reactive the lime was as it slaked, as you can see in the video below. This held a particular interest for me, because Scarborough has a great many historic buildings constructed in ashlar masonry, a large number of which have at some point been repointed in hard cement mortar. With ashlar in particular, the joints are fine and the stone finely dressed, so an unsuitable cement pointing is both conspicuous and damaging. Advising owners on these properties, and on the use of a correct and compatible lime pointing, is an increasingly important part of what we do.
More than mortar: time with fellow surveyors
One of the less tangible but equally valuable aspects of an event like this is the chance to spend time with others in the profession. Alongside the formal CPD, I was able to meet up with two other local surveyors, and it proved a brilliant opportunity for general networking and for talking through the day-to-day realities of residential surveying. Conversations like these, comparing approaches, sharing experiences and discussing the issues we each come across in the field, are every bit as useful as the technical content. Surveying can be a fairly solitary job out on site, and it benefits enormously from a strong and friendly local network.
It was a real pleasure to catch up with Nicky Demaine of Keystone Surveyors and Chris Hewison of Sherlock Homes Surveys. If you are looking for a residential surveyor in their part of the region, both are well worth speaking to.
What this means for our surveys
Understanding traditional construction is central to how we carry out a Level 3 Home Survey. When we inspect an older solid wall property, we do not simply record dampness and move on. We consider why moisture is present: whether the cause is genuine penetrating or rising damp, condensation and lifestyle factors, blocked sub-floor ventilation, or cement render and pointing trapping moisture and preventing the wall from remaining vapour permeable. Each of those has a very different remedy, and getting the diagnosis right can save a homeowner a great deal of money and unnecessary disruption.
If you own, or are thinking of buying, an older solid wall property in the Scarborough area and you would like it inspected by a surveyor who understands how these buildings are meant to work, we would be glad to help.
If you are interested in a Level 3 - Home Survey, then please feel free to visit our Home Buyers Page.
Please also consider visiting our Book a Survey page, where you can see our availability and get a price quote for your new home survey. Thank you for reading this blog, and I hope you found it interesting! Best wishes Ricky Savage Founder and Building Surveyor
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