Friday, 13 May 2016

The use of lime putty.

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 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 people will not use 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 10 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.


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 their joints. 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 colour difference but an NHL 5 is like using a sledge hammer to crack a nut. Totally unnecessary.

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 putty presented itself I couldn’t resist.

I think it’s partly to do with the fact that it’s older than NHL and less cementitious. It harks right back to Roman and Egyptian times and is what the masons and builders would have used all over the world prior to Smeaton inventing natural hydraulic lime back in the mid 18th century. Putty is a non-hydraulic lime and in essence this means it won’t set underwater and won’t cure if applied to damp areas. In direct contrast, hydraulic lime will set in the presence of moisture and is slightly different (and easier) to work with. Alongside many variables to deliberate one needs to carefully consider the amount of care which needs to be taken when mixing. If, for example, one uses wet sand then all that’ll happen is your mortar will turn to slop. But carefully planned, the use of putty can be a rewarding experience both for contractor and client.

Sunday, 28 February 2016

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 country where strangers were guarded 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 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 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. Gypsum is very good at this. If you bear in mind that just because a product holds water does not mean it is porous 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. This automatically improves insulation – especially if it’s a hemp lime plaster - and controls damp. 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.