Saturday, 1 December 2018
Chalkstone repointing and repair. Period property maintenance.
Uffington is famous for the legendary prehistoric equine figure carved into the scarp. The white horse itself was created by digging trenches and filling them with chalkstone – no small task even by today’s standards. What sets this built environment apart from other areas in Oxfordshire is that very same chalk stone. Villages such as Uffington, Ashbury, Coxwell, Woolstone and Fernham are peppered with these ancient properties (many of them listed) complete with their thatch roofs and cottage gardens which tell of a time long ago. These testaments to a bygone age – some dating back as far as the medieval age – are an important part of our heritage. However, owning a property of this historic significance does not come without its responsibilities and complications.
As a buyer, owner or surveyor, some knowledge of how to report on or maintain such a property is invaluable. Knowing what to look for is essential. If you’ve never bought an ancient piece of architecture or if you’re a surveyor with little experience of examining and reporting on the state of repair of such a property then I hope that what I write below may inspire you with enough confidence where the purchase of such an estate is concerned.
It’s time to forget about clicking and dragging or the speed of broadband. Very little of this current age, or its timeframes, is applicable where the maintenance of a chalkstone property is concerned. Although modern materials were initially encouraged by anyone involved in the building trade, those now involved in sustainable restoration and the maintenance of period properties frown on their use. As a rule of thumb, the idea of pursuing the use of any type of modern paint, mortar or plaster must be completely discarded. By its very nature, chalkstone will not tolerate them.
Look for the liberal use of cement on the property as its use can be likened to Kryptonite on Superman. It will, simply put, destroy houses. Yes, I really mean that. Chalkstone is soft and therefore requires that a mortar which is even softer is used to bed and repoint it. The mortar acts as the sacrificial element to the build so that when it’s attacked by the weather it’s the mortar which sustains the damage. Cement is much stronger than chalkstone so it is the stone itself which gets offered up thus leaving all of the cement intact. The problem with chalkstone properties is that many builders and DIY enthusiasts have, over the decades, used cement with almost gay abandon and many of the properties are repointed with it. This would be fine if the stone was granite as that’s even harder than cement. But chalkstone gets very easily blighted. Every day the cement sits in the joints, more physical harm occurs. It’s best practise to get it out and replace it with lime mortar.
People often tell me that old houses need to breath. They don’t. The very act of breathing involves the inhalation of oxygen and the exhalation of carbon dioxide. This does not happen with old houses. The truth is that moisture laden air which comes from the ground up passes out of the joints between the stone. This movement is made possible by minute bridging networks which enable water molecules to pass out into the atmosphere. It also means that moisture which sits on the face of the stone is pulled away though the lime mortar and similarly wicked away. Chalkstone is the most porous building stone available and the use of cement traps moisture and rots stone. Any evidence of cement on the outside of a chalkstone property means trouble. So if you’re buying or reporting on a chalkstone property then careful attention must be paid to the exterior of the property as repairs to chalkstone are costly.
Why, you may ask? Let me put it this way: when I repoint ordinary bog standard limestone I know that – depending on the time of year – I can be fairly laid back about attending to the drying mortar and so I can be fairly relaxed about the whole process. As far as chalkstone is concerned, its porosity means that I have to control for suction. This is not without difficulty where plastering and rendering over chalkstone with lime is concerned but much easier when repointing. The type of sand has to be well chosen otherwise it’s an uphill struggle. Issues are compounded by the rarity of replacement chalkstone and the fact that expensive specialist fillers and costly organic pigments have to be employed where repairs are concerned and you’ll begin to understand why a property suffering from the use of cement repairs and repointing must be viewed with a cautious eye.
However, it's It’s not all doom and gloom and doesn't have to be a costly drain. Living in a period chalkstone property can be a rewarding experience and you should not be daunted by the challenges. Let’s have a look at a few:
· Damp. If there’s damp in the property then it won’t be there by magic which means you won’t need a wand to cure it. Nor will you need any expensive damp proof treatments. These houses were all built without damp proofing but unfortunately most of them now have it. At one point banks wouldn’t lend on a property which didn’t have some evidence of an injectable damp proof system so they became quite popular. Nevertheless, if there’s damp then the likelihood is it’s there because the membrane under the concrete was put down poorly and some moisture may have seeped up over the years. All you need to do is hack out the old rotten concrete and backfill with some new. Oh, and don’t take any notice of the chemical damp proof course as they’re a total waste of time. Those who sell them would, in a different era, have made their living from selling snake oil. What they need are hot-mixed lime mortars as these have the largest pore size so moisture can be evaporated away from the stone thus leaving it nice and dry.
· Rising damp. This is almost an oxymoron and didn’t even exist until damp proof salesmen started selling their wares. When moisture can’t escape it rises. If it can’t escape then it’s because it’s been waterproofed in. Cement will do this. Cement render on the inside and cement repointing on the outside means moisture has nowhere to go except up. That is until gravity holds it in place. Tanking and other such odious and reprehensible practices will result in moisture unable to permeate beyond lime plastered walls. Condensation will also sit on walls plastered with inappropriate materials such as gypsum and the result will be mould.
· The wrong paint. There’s no point in having porous walls and spending your hard earned money on non-porous paints. Beautiful clay or lime plaster needs to be painted with traditional paints such as clay, lime and chalk. Failure to apply these will result in moisture retention and you’ll get mould.
· The wrong plaster. Most plaster systems today are applied in two parts. The first is the application of two coats of cement render. The second is the application of gypsum plaster. Old properties have little or no foundations and cement won’t move with the building and it’ll crack. So will gypsum. This is also pretty rubbish where condensation is concerned. If your house has solid walls i.e. no cavity and no airbricks you’ll get moisture build up in the air. When you go to bed the moisture held as vapour will become liquid and sit on your walls. What happens is that people don’t understand how old houses work and once signs of condensation appear they call in the damp “experts” and the whole miserable business repeats its self.
· Plasterboard and insulating form based boards such as Kingspan. Simply put, these are just wrong. For old houses you need woodwool boards and sheep’s wool insulation. Kingspan is made from horrible petroleum derivatives which are about the least environmentally friendly and toxic products you can ever use. It’s also very flammable whereas sheep’s wool is the exact opposite. Plasterboard has no heat retaining ability and you cannot skim it with lime. If you insulate your period property with modern products you increase humidity. Sheep’s wool insulation draws moisture out of the air and holds on to it which means humidity decreases.
· A healthy house: studies have shown that we spend about 90% of our time inside and yet most of the air, even in city environments, is healthier outside than what we breath indoors. Care must be taken when choosing products where your children sleep.
· Lime plastering over gypsum. Don’t do it. It’ll crack.
· Using plaster which isn’t lime. You have to use lime plaster on old buildings for four reasons. One, if you use anything other than lime you’ll get damp. Two, lime plaster isn’t affected by movement in older houses so it won’t crack. In direct contrast, cement and gysum will crack. Three, builders and plasterers PVA coat the substrate. They use products like Unibond to seal the wall so they can control suction. Bonding agents waterproof walls and you get damp. Four, if you use cement and gypsum internally in old houses you’ll get condensation.
· Damp meters are a waste of time. All walls in period properties, by their very nature, have a higher moisture content than their modern counterparts. This is called hygroscapic water. Any surveyor who points a damp-ometer at a listed building should be struck off. Any surveyor who even mentions the word damp but who hasn’t turned up with at least £10,000 worth of surveying equipment should be ignored. If you see damp then it’s likely there’s a damaged DPM, water ingress from a damaged drain or gutter, or another easily identifiable source. And if a surveyor ever recommends a French drain at the bottom of an elevation then just shoot him. Seriously.
The bottom line is this: if you have an old house and you employ tradesmen they will use the wrong products on your property and these will be detrimental. If you use builders who are not specialists in period properties then they will cause damage to your property and this will cost you or future owners money. If you use specialists you will have to prepare yourself for the long haul because specialist products became unfashionable because of the cost of the required time and skill and therefore the encumbent expense associated with them. It’s time to go back to basics and dig a little deeper into those pockets. Or, just don’t buy an old house.