Hugh Dorrian of Stoneware Studios tellshow old stone and brick walls that have been coated in cement render, benefit from the re-introduction of lime render on the outside or lime plaster inside.
Lime mixes have been used for plasters, render and pointing, not for centuries, but for thousands of years, and they hold an important place in the repair and conservation of older buildings in Ireland today.
I asked Hugh Dorrian, owner of Stoneware Studios, to introduce us to the wonders of ancient lime mixes, a material he aptly describes as “the Gore-Tex of the building world”.
“Breathability, water repellency, sealing walls, water-proofing — it can all get a bit confusing,” Hugh explains, “But thinking about it logically, I like to think of the buildings we live in as another layer of clothing we wear.
"So with these walls, the outer layer, we don’t want to let any water in but we also don’t want to have an overcoat that will never dry out if water does happen to get in behind that outermost layer.
Lime reduces water getting in but, most importantly, it doesn’t trap water either, it allows water vapour (which is a gas, suspended in air — hence the term “breathability”) to evaporate through the wall. Lime works really well with the Irish climate because of that.
Mixing it up
If you own a house built before about 1900, it almost certainly has lime in the walls.
More often than not, the lime was made locally, mixed with sand and water to make a sticky mortar for building with stone and brick and then rendering and plastering.
Lime is usually off-white or slightly creamy in colour, rarely cement grey.
“Dark grey hard brittle mortars are usually cement-based. To the trained eye, you can tell a lime just by a visual inspection, but if you want to know more about what type of lime you have you might need to send us a lump of the mortar,” he says.
Some limes are very strong and long-lasting and some lime mortars are very weak and crumble in your hand. Either way, there’s a modern lime that is suitable for repairing it.
“Mortar made with cement is incredibly hard and dense,” Hugh explains. ‘It is not water repellent and yet, disastrously, is impermeable to water vapour. It will get wet easily and when it gets wet it stays wet. So, if there is cement present, there’s every chance that that dampness is not far away.
What you should be aiming for is having materials in old buildings that have some resistance to water getting in and, at the same time, are very fast to dry out. That’s where lime and breathable paints work. So if you have a building that is susceptible to dampness then lime will manage the water so much better.
"We’ve been making and supplying lime for over 20 years and, without exception, stone and brick walls that have been coated in cement render and as a consequence holding water, greatly benefit from the re-introduction of lime render on the outside or lime plaster inside.
“The two main ones are flexibility and breathability. Flexibility means fewer, or no, cracks, and breathability means simply that walls dry out fast. We debate and test these ideas at our courses in Youghal, and, once everyone is satisfied that the materials do actually work we can show you how to use them.”
What about using hydraulic lime for stone and brick repairs?
Hugh continues: “Eighteenth-century Roman cements, limestone window sills, Youghal or Belvelly brick, Portland door- and window-surrounds, Bath stone ornamentation, old red devonian sandstone and, most importantly, our pale grey carboniferous limestone that is native to Cork city, can all be repaired with lime. It’s just a matter of understanding which lime to use, and what other ingredients need to be added to make it work.”
As for insulation choices? “The same principles apply.” Hugh emphasises:
“If they stop moisture from evaporating through the insulation you trap moisture behind the insulation layer and you can end with stagnant water within the wall.
"Where there’s water and heat and a little oxygen you will have life — mould, mildew and rot. Fully breathable insulations such as Secil Corkboard, EcoCork plasters, redstone silicate boards and other insulating plasters allow the walls to continue to breathe while improving the thermal performance.
"Corkboard, used in combination with lime plasters, really is the perfect blend of breathability, very good thermal conductivity, totally and genuinely natural and renewable. They have a long pedigree as an excellent insulator for example at The Butter market and the various Cork breweries going back over 100 years.”
Damp control is something that troubles many well-meaning contemporary cottagers. Beyond digging out French drains around a stone/rubble-stone house — what should be avoided?
“You can have all the breathability in the world but if the water keeps flooding in to your basement,” Hugh explains, “you’ve going to have to reach for something beyond lime plaster. Cavity membranes can solve dampness issues if the traditional way is just not enough.
“Other than dealing with the immediate and annoying problems of damp patches, blistering paint and powdery salts appearing in the most unexpected places — the solution needs to be long term. How do you manage water? Where is it going if it is not coming in? These are the questions that need to be addressed.”
Can I handle lime materials DIY or should I hire in a specialist? “Small repairs, touch ups, lime-washing, shelter-coating, and maybe a bit of re-pointing is within most people’s capabilities, with just a little guidance” argues Hugh.
“After that, wholesale re-pointing, rendering or plastering is more a job for those who are fully trained.
"Luckily in Cork we have a great pool of talent of men and women (one of the best masons in Cork is a woman, by the way) who are experienced with lime — very good lime plasterers, stone wall builders, bricklayers and painters who have no fear of lime and have full confidence in what they are doing.
All the prestige buildings in Cork — St Finbarr’s, North Cathedral, City Hall, Shandon, UCC, Fota House, the Courthouses, most of Patrick Street (even the side of Penneys) - have all been repaired with lime in recent years and by local people.
“We’ve been running a single-day course on Renovation with Lime for many years and it’s as popular as ever with our next one fully booked, prompting us to set another date at the end of July.
"We try to give sound advice and properly researched and tested products that work, and deal with people we like and who like us — simple enough, really.”
The next “lime day” training at Stoneware Studios at Pillmore, Youghal, is scheduled for July 12. Call 024-90117 or visit stonewarestudios.com.