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 or no 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 (or the reporting on) 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 three parts. The first two involves the application of two coats of cement render. The third 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 which will result in black mold.





· 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 hygroscopic water. Any surveyor who points a damp-ometer at a listed building should be struck off. Any surveyor who tries to measure moisture in walls 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 drain or gutter, or another easily identifiable source such as the wrong plaster, tanking, cement or gypsum plaster. 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.

The use of quicklime mortar.

It’s been a while since I had a rant about the use of lime in comparison to cement but as Doris and I aren’t doing anything today I may as well pen a little invective.

The trouble with the building trade is that it’s very slow to change. Mention continuous professional development to anyone in construction and apart from those who wear the white collars or have higher education qualifications you’ll get a dumb look. The reason for this is because unless a product will speed up a process or coin a larger profit then trades will not be drawn to using it. In fact, you’ll have to drag them kicking and screaming if you want them to use traditional materials  or natural products.

In the case of lime it is shunned because it takes more time and skill than modern products therefore it is regarded as something which will cost more to use and therefore affect competitiveness where quotations are concerned. Cement is where it’s at - unfortunately ease of use is promulgated in the construction sector to the detriment of the built environment.

Nevertheless, this is not where members of the general public are. People have moved on. Home owners are savvy. They research. They hear things on the grapevine and get themselves up to speed. Only 15 years ago I was struggling to inform would-be clients that lime was necessary on their old houses. Not anymore. Thanks to the internet, pretty much everyone who contacts me has a basic understanding of the mechanics of older properties. All I need to do is help them out where a bit of practical knowledge is concerned and maybe quell fears they have regarding appropriate conditions for use.

The problem many people in the English speaking world now have is that when they give the average builder the opportunity to build or repoint using lime, the first thing he does is knock up a bit of lime mortar with far too much sand and then add a bit of cement. Ask him why and he’ll tell you “it sends it off quicker”. In his eyes the addition of cement is needed for a quicker set. He'll also believe that the lime makes his mortar more porous so that’s got to be better than just cement on its own. In his world, that’s lime mortar. It’ll also last longer because it’s harder.

Wrong. 

You’ll get about 40 years out of cement repointing and during this time all manner of damage to your stone will be being done. In direct contrast you can expect between 70 and 200 years out of lime depending on type of stone and amount of weathering. Even today I'm still working on buildings with the original lime still in the joints of 300/400 year old houses. Time is an excellent measure of durability. 

If you want to use a landmark as a comparison for longevity then try the Tower of London. That was built in 1078. If you want another example there’s always Hadrian’s Wall.

The Slovenians had the right idea and instantly banned Portland Cement. In fact, it’s only really been the English speaking world which embraced it. If you want proof, try telling an Italian stonemason in the heart of Puglia that he’d be better off with a bag of Rugby general purpose and see how far you get. Although he will be quite used to seeing failing mortar joints, they’ll be degrading on buildings which were originally built in places like Marziolla around 1550. 

In direct contrast we have Bob the Builder. I take great delight and merriment from reading posts on self-help ask a builder websites where builders and anyone with an interest in construction are quite happy to proffer their "expert advice". The last one I read was where someone wanted to use lime on an elevation of their property which experienced buffeting from the weather. One guy suggested using NHL 5 half way up the elevation and 3.5 for the rest. I was amazed. Not only would there be a very noticeable colour difference but an NHL 5 is like using a sledge hammer to crack a nut. Totally unnecessary and potentially damaging.

Oh, and if you want a laugh: I actually heard of one guy recommending the usual cement/lime mix on aged Cotswold ironstone. The reason? To stop the rain washing out the mortar.

I was astonished..

But I digress. When I first started working with lime it was always natural hydraulic lime (3.5). It took years to understand its temperament and even today I occasionally get caught out. But I always like to keep myself challenged so when the opportunity to use quicklime presented itself I couldn’t resist.

It's earliest use can be traced back to 12000 years BC in ancient Israel. In direct contrast, Smeaton invented natural hydraulic lime back in the mid 18^th century. Having used quicklime in hot mixed mortars since April 2020 I've now ditched NHL and lime putty in pointing and plastering mortars. I now only use putty for top coat plasters. 

 

The problem with gypsum plaster

Why to use lime plaster when comparatively cheap gypsum plaster is available.

If you could go back in time you’d find small villages and hamlets scattered with houses of cob, wood, thatch and stone construction. There is little to no evidence of these today but if we could take a walk down the main track, in say the year 1200, you’d probably find you got lots of attention from the domestic dogs as well as the locals who'd look at you askance. 

In a self-policing society where strangers were reguarded with suspicion, dogs were the safeguard of many a poor subsistence farmer living in the most basic of accommodation. However, if you wanted more security and potentially a better class of living then a dwelling within the city gates of places such as York, Worcester, Newcastle - upon - Tyne, or Berwick on Tweed would be your target providing you didn’t mind the incumbent issues of cost, smell and overcrowding. 

As you can imagine, lifestyle then was very different to its modern day equivalent. Houses were predominantly shelters from weather and places to sleep. And unless you were of means, the idea of being particular concerning plaster-work would be pretty low down on your remit.

Traditionally, both internal and external walls were covered in just about anything anyone could lay their hands on including mud, clay, dung and straw. Lime plaster for the masses was yet to come and would act in the same way as the above in that it helped to windproof homes as well as allowing rain to soak into the plaster rather than the stone. As lime garnered popularity its application often consisted of one coat of lime mortar pasted so thinly over the wall that all it resembled was a bad case of repointing. Nevertheless, the moisture inherent in the mortar evaporated as the weather improved. The lime and sand mix also aided the displacement of water which may have soaked up from the ground. 

If one wanted a more even surface then the first application of mortar was scratched to form a key on which to apply a more even second coat. Finally a third coat was applied for internal work and this consisted of a higher ratio of lime in tandem with finer grains of sand which is now commonly known as plaster.

In sum, a coarse mix of lime and sand simply thrown onto the surface of the wall would be an adequate covering but when a smoother more high quality finish was required then the size of the grains went down and the amount of lime used increased. Obviously those who owned smarter and more prestigious buildings were the ones who enjoyed such luxuries.

Lime served its purpose for thousands of years until after the Second World War when comparatively cheaper cement render and gypsum plaster was employed. This was predominantly out of economic need as houses had to be built quickly because many had been destroyed in the Blitz. 

By now, damp courses were being employed in every build.

Membranes were being used to restrict moisture from entering a property at its base and this now meant there was less need for lime mortar. Solid walls became a thing of the past meaning cement render and gypsum plaster could be used. This, in tandem with the manufacture of tougher bricks, cavity wall and the use of air bricks to encourage airflow, meant that lime had had its day. The upshot was that skill with lime became absent; and very quickly. 

 

This was fine where new build property was concerned but the need for lime remained where the maintenance of older properties was required as these still needed porous materials which would facilitate the expiration of moisture. That’s when the cowboy contractors and snake oil salesmen moved in. 

With the greater use of cement came all of the problems of which older building now suffer. As cement was applied this meant that there was no means of escape for moisture therefore many owners of older properties resorted to damp proof treatments. Companies which offered these happily charged unsuspecting and ignorant members of the general public hundreds – sometimes even thousands – of pounds to eradicate their problem. However, all they were left with were empty promises based on “scientific proof" that certain products would totally and with absolute certainty eradicate moisture. Yet nothing can stop this from traveling higher up a wall if it’s been coated with cement as this will not allow it to escape. The term rising damp was coined and a whole industry evolved around it. Contractors used their products on new buildings and assumed incorrectly that they would do the same job on older properties. What owners were left with were products which would totally waterproof their properties or which would hold water within walls. 

 

If you bear in mind that gypsum plaster is a product which allows for the passage of moisture and has some porosity then you'll see my point. All that happens is that it absorbs moisture from the base of a property and holds on to it. Thus, when paint is applied it will only be a short while before it peels off. When you have a damp wall then often the best solution is to totally remove the gypsum and cement and apply lime. Adding components to lime plaster such as pumice, perlite and glass can also improve insulation – especially with hemp lime plasters. Combined with the use of porous paints the issue of damp becomes a thing of the past and so does condensation.

 

In sum, owners of period buildings who employ the use of gypsum plaster must prepare for certainties. One of which is cracks. Older properties are set on less than substantial foundations and are therefore prone to settlement. Lime plaster will accommodate this but inflexible gypsum will not. So mold, condensation, cracks, poor insulation quality, rising damp and salts bubbling up from the surface of your wall are the mainstay of gypsum plaster.

Some of the pitfalls of listed building ownership and the need for professionals

If you're new to the concept of listed buildings, or are currently thinking about having work done to yours and are not sure about which materials to use or the possible legal implications concerning alterations (however minor), then this is for you. 

The definition of what it means to be a listed building owner is one which states that you are charged with the guardianship of the building. You might own the title deeds but your ownership is in name only. The Conservation Department of your local council can exercise its rights over you as far as upkeep, maintenance and alterations are concerned. There's just so much you can't do so if you're desperate to knock down walls and put your modern stamp on an old building then it might be wise to look for something which isn't listed. 

The aim of this article is to give owners and potential owners a greater understanding of their rights and responsibilities. Hopefully it will enhance the ownership experience and help you to add value to your house whilst making it more saleable. 

Firstly, contractors. With ready and willing hands only too eager to pocket a pile of hard earned cash in exchange for some inappropriate work it’s rare that one comes across a listed property which has not had the addition of cement for rendering and repointing over the last 50 or 60 years. In fact, it’s likely that 98% of listed buildings have had the wrong materials used on them at some point. Not only might the house come with the addition of icky cement, you may also find walls covered in gypsum and none breathable or plastic paint. If you're in the market to buy and you spot that gypsum might have been used then make a note and ask your surveyor to check it out. Look at the walls and if they appear really flat - a smooth almost mirror finish - then this might be evidence of a gypsum plaster. Check to see if an effort has been made to make the interior look as smooth as a new build and bear in mind that an uneven surface is actually a good sign. Don’t be afraid to ask the vendor if they can prove they instructed a contractor who used lime – an old invoice could go a long way to dispelling fears. If gypsum has been used then it might be worth asking the current owners to consider a reduction in price as it means there will  be  trouble ahead as gypsum will only last a few decades and will blow once moisture gets behind it. It will also crack where there's even just a fraction of settlement.

A more common and quick to appear issue of modern plaster is the fact that condensation rapidly gives rise to mold. The problem being that it will hold moisture but is not porous enough to aid its evaporation.This is because gypsum plaster is actually very porous but not in a good way. Think of a sponge and how it holds on to moisture.

If the pink stuff or cement has been used in any area of the house then consider how much its removal might cost as it could be an expensive job or a time consuming pastime for you. 

When mulling over a purchase it's worth the effort to check out whether listed building consent has been sought for previous work. No record will indicate lack of consent. And this cannot be given retrospectively. Conservation departments may go so far as to allow that repairs have been made but it is always noted that that these were made without permission.

Thankfully, when buying a property, it is likely that your surveyor will be of great help where highlighting the incumbent issues inherent in the use of inappropriate products. One concern relating to cement mortar repointing will be the depth to which it has been applied. Deep might result in recommendations to leave it alone as damage to the masonry is likely should its removal be attempted.

Although you might be very confident at DIY, it's a very different state of affairs with a listed building. With modern builds a splash of paint or a quick repair might improve the property but once you start making changes to a period property then the results might substantially reduce its value. In many cases, using professionals from the smallest to the largest repair is often the best way.

I decided to have a ring round a few chartered surveyors to test a few hypotheses and was recently talking to Charles Brown from Cotswold surveyors (http://www.cotswoldsurveyors.co.uk/) who not only stated that contractors who understand traditional products are an absolute necessity but also employing the services of a specialist architect for large jobs was a prerequisite when making major changes to a listed building.

All surveyors are very observant and have trained for years to achieve their level of understanding of the way buildings work. Most are experts in the mechanics of older buildings and can spot an inappropriate repair a mile off. If you have not sought permission for one of these then it could result in potential buyers removing their offer. Hall and Ensom (http://www.hallandensom.co.uk/), for example, are another like minded company of surveyors who are happy to espouse the virtues of traditional products and the use of professionals on period homes. Speaking to them recently revealed that it can be helpful to have the input of the vendor during the survey as there'll often be questions about the products used for repair and refurbishment i.e. whether the paint which has been used is a porous clay, lime or chalk based product.

And even if everything appears in order, the path to period living can still be fraught with difficulty. For example, there are often issues with lenders such as banks and building societies. Although attitudes are slowly changing, for some reason a few believe that it would be unwise to supply funds unless there's evidence of a servicable damp course. Of course, as a listed building owner, the last thing you would want is one of these as they create more problems than they could ever solve. 

What could also trip up the selling process is a good solicitor. If experienced enough, he will be able to spot whether a potential seller is trying to pull the wool. For example, new laws of disclosure as from 2014 now state that a seller must provide information concerning work which has been done on a property especially if it will interfere with the future enjoyment the new owner expects from the house. I can see it now. "So Mr Jones, you've stated in your disclosure report that you've had no work done on your grade two listed property over the last ten years yet the estate agent's details state that this is a property which benefits from extensive recent updating. Did you apply for listed building consent? You didn't."

It could spell the end for the cost cutter, bodger and cowboy owner where listed properties are concerned because being one or employing a rogue could make a property unsaleable. The reason? Lenders will only lend if a potential buyer is able to get insurance against work undertaken that may have been done without listed building consent. If the survey highlights the possibility of such work then the buyer might not be able to move forward and you could end up having to reduce your price for cash only.

My main priority at this point is to try and advise you, coerce you, cajole and persuade you to only ever use natural materials during refurbishment and repair-work. Natural is always best when it comes to older properties as modern products tend to work against the house rather than with it. Using lime lime based products on listed buildings is always preferable. Not only from a personal health perspective but also from a legal one as the Conservation Department have powers to bring owners to the courts. And with very expensive outcomes. It’s certainly not unheard of for large fines to be imposed on those who’ve effected repairs without consent or have demolished parts of the building without permission. In the worst case the ultimate course of action (although extremely rare) is imprisonment or the confiscation of property. 


Should you choose to go down the route of employing contractors who are unused to working with traditional products then I can give you a hint as to what you may encounter. As a craftsman I've had the displeasure of working for owners and with tradesmen who are only too willing to apply cement and gypsum to properties. I've even asked them why. The answers usually reflect very little knowledge of the requirements of the local authority. They are simply unaware of the requirements of these bodies and are also unaware that products other than the ones used on modern buildings must be used on old houses. Most have less than a modicum of knowledge of the mechanics of older properties and their knowledge of their own products is limited.

If you do not instruct a plasterer to use lime then the result will be two coats of cement render and a couple of applications of multi-finish. You may be informed that the first two coats are breathable as they contain lime but what won't be mentioned is that it's hydrated lime which will be shovelled in alongside the cement. All you'll end up with is double waterproofing. It'll be finished with Multi or Board Finish and this is also non-breathable. The result will be that moisture will not pass through the wall and you'll get rising damp, problems with condensation and also the issue of salts rising to the surface of the plaster causing bubbling. 

Incidentally, there's a current trend for manufacturers of some cements based renders to refer to them as 'damp control'. All this means is that moisture will be stopped from evaporating away from the surface of the wall because the product will have waterproofed it.

So staying away from gypsum plaster and cement is always advisable as the upshot is that their use will almost certainly result in cracking due to seasonal changes and thermal movement. All newer products including Tarmac's Limelite have waterproofing qualities as well. Basically this stuff is exactly the same as a 6:1:1 cement render mix using Perlite to substitute some sand. Tarmac say it's a favourite of the conservationists. But try specifying it with the Conservation Department and see how far you get. 

But I digress. Back to gypsum: one of the eventual outcomes of using it might be that it will simply peel away from the surface of the wall should there be any moisture behind it. The reason for this is that gypsum comes in two forms: either mildly soluble or totally waterproof. In direct contrast, lime will allow moisture  to pass through it and simply wick it away. Although some contractors will say gypsum is porous, just because something holds water does not necessarily make it so.

As mentioned earlier, many contractors are simply unaware of the implications of working on period properties and most are certainly ignorant of the fact that they too can be prosecuted for undertaking inappropriate work on them when they’re listed. What you'll get from most plasterers is Unibond and render, or PVA and render, or PVA and British Gypsum's One Coat because that can look like lime when it's trowelled down. What you might even get is a light Multi Finish skim over your existing lime and that will be considered normal and good practice. 

If you'd like to do a bit more research then I've found a youtube clip on the use of gypsum versus lime mortar and also one on the virtues of using natural paints which you may find useful watching.

https://www.youtube.com/watch?v=iZlqzASDN_U

https://www.youtube.com/watch?v=4OgjftJ3kU8

There’s also the author Marianne Suhr who is an expert on older buildings and she’s written a number of books which are available online. However, should you require something more brief then there's always Period Living magazine which is out every month and costs only £3.70. It’s always good to familiarise yourself with as much as you can as forewarned is forearmed.

Correct aggregates for repointing where lime mortar is concerned

Firstly, let us take the ordinary and mundane subject of sand. As we all know, that which is used to lay bricks and stone is mostly sold from quarries and local builders’ merchants. It's called screened sand, soft, or building sand and is made to a particular recipe where different types of fines are combined with larger grains. But what if you want a soft sand for building or pointing with lime mortar? Can you throw a few bags in your boot and get going with a project? In short, the answer is yes, of course you can, but after reading this you might not consider it an option. The main reason for this is that building sand is too soft and this means the lifespan of your mortar will be reduced if you use it. Care must also be taken where colour choice is concerned as soft sand comes in a multitude of colours and if you or your contractor pick the wrong one then you’re in trouble.  You may even devalue your property.

At this point I need to be careful otherwise I’ll run the risk of revealing trade secrets so it’s probably best to keep this brief: for repointing with lime mortar you need a combination of two types of sand and both have to be washed. However, most trade and DIY outlets do not supply what's necessary. So if you use unwashed sand then impurities which have not been removed will rise to the surface of newly applied lime mortar.

Sharp sand, on the other hand, has very little influence on colour. But it will have a direct affect on texture and therefore finish. Ordinary sharp sand from a quarry or builders yard is a fairly uniform texture with aggregates large enough to make it qualify as sharp. In sum, it’ll do the job but it’s nothing special. It’s the type of aggregate which is perfect for laying patios or putting down a base for a shed. However, if you want sharp sand which is going to make the mortar in the joints of a period property look sublime then you need to extend your search beyond the average home improvement retailer. This is because when lime mortar is brushed, the larger particles of sand are brought to the surface and only a top quality purposely blended mix of sharp and soft sand will recreate the depth of shade and texture needed to replicate the highly desirable effect which is so enticing where beautifully maintained period properties are concerned.

I use what I consider to be the perfect blend of sand. It consists of a mixture of soft and sharp sand to the specifications which my experience dictates is correct. It looks superb, there’s no colour leaching and the aggregate sizes and colours go together to create the ideal tint which complements natural stone. Not only this, but it also conforms to BS EN 13139:2002 Aggregates for Mortar which is the current standard.

Secondly I wish to highligh the issue of exacting standards in the use of natural hydraulic lime (NHL), quicklime and lime putty as all are obviously a priority of mine. They're flexible and porous and need nothing added to them except the appropriate sand. But unlike many other contractors I do not adhere to the widespread practise of adding cement to make my mortar cure more quickly as this pollutes the mix and simply turns good quality lime mortar into plasticised cement mortar. This is the last thing any owner of a stone built property needs – specially one which is listed. 

And finally there’s the finish. Lime must be brush finished and should never be trowel finished. However, it takes time to dry sufficiently before any  brushing should take place. Brushing prematurely not only results in cracks but also in the appearance of what look like damp patches. They're not really damp patches, it's just that the brush forms the calcination coat and brushing too early creates a mottled effect in places. Although over time this does fade, it usually takes a couple of years. 

Furthermore, omitting any of the brushing stages - or brushing improperly - not only results in a poor finish, but any lapse also means that imperfections remain as these are never revealed and therefore never attended to. None of this may matter to a potential customer if price is the only issue but employing a contractor who fails to attend to mortar correctly during its drying stages results in a job which will not stand the test of time.

In sum, lime takes time and the process of lime mortar repointing is very labour intensive. Mess up on something as simple as wetting up joints before applying mortar and things start going downhill rapidly. Leave it too long before brushing and things look even worse.

Recently I was discussing the merits of lime after I’d removed a wall full of horrible grey cement mortar and mentioned the fact that you’ve got to fight with it to know it and only when you’ve fought with it for long enough will you be its master. But mastery is  not about thumping it into place and being boss. It's about the relationship you have with it and how you must allow it to be what it is and work with it  and not against it. The reason for this  is that it's a natural material and these need comprehending. If I were ever to use an analogy to describe it then I'd equate working with lime to training a dog. At some stage you realise that many of your ways aren't productive but you have to get to that point before a lifelong relationship forms.

Anyway, I hope what’s written above has been informative in some way and that you can now see at least some of the reasons why the Conservation Department requires an example square metre before allowing contractors loose on listed buildings. 

Thanks for reading.

If you would like further information concerning the use of lime mortar please see the ‘blogs links and articles’ page at michaeljamesdesign.co.uk