Thursday, 22 July 2010

A bad workman blames...

All is not peaceful in the world of lime, it would seem.
Following the success of a television series about Griff Rhys Jones’s project to restore Trehilyn, a farmhouse on Strumble Head in Pembrokeshire, Griff produced and presented a second television series about the restoration of the farm's outbuildings.

It followed the now-familiar formula of TV building programmes, with idyllic shots of natural scenery intercut with anxious pieces to camera about slipping deadlines and minor crises. All very cosy and formulaic, but pretty undemanding telly for a September evening.

Unfortunately, however, one of the ‘disaster’ vignettes has proved rather damaging to the world of building conservation and to the reputations of two companies who should be celebrated as the 'good guys' rather than cast in the role of villains.

Griff wanted to restore two derelict buildings on the farm and convert them into holiday lets. This being Pembrokeshire, he wanted one of them to have a common feature of many buildings in that part of Wales, a grouted roof.

A what?

Grouted roofs are an oddity; a classic example of bodging that has now become part of the vernacular, but one which is as ‘authentic’ as a Derbyshire goitre or bowel cancer in Scotland, if truth be known.

The practice stems from the way roofs were built and the parsimony and poverty of the farmers in the region. Pembrokeshire roofing slates are heavy, lumpen things, more than twice the weight and thickness of the more widespread Welsh slate. Traditionally they were fixed to the roof using square oak pegs forced through a round hole in the slate and simply hooked over the battens. To keep them from lifting, the slates were then ‘torched’ into position from below with a fillet of lime mortar.

It’s a simple and effective method of fixing, but one that requires regular maintenance. The roofs are incredibly heavy, and if allowed to decay, the structure suffers. The pegs shrink and fall out of the holes, allowing the slates to slip, and the sheer weight of the roof can pull the battens loose, resulting in the roof parting company at the ridge and slumping towards the eaves. To remedy this takes skill and money – and money was in short supply in Pembrokeshire in the latter years of the 19th and the early 20th century.

So, as a classic bodge, the farmers came up with a solution. A bag of the new miracle material, portland cement, was stirred up with water and sloshed all over the roof in a slurry so it would set and hold the loose elements in a hard shell of cement. To stop the roof slipping down over the eaves, that other new wonder-material - barbed wire - was used, with lengths nailed into the wall plate and taken up over the ridge and down the other side to secure the loose courses in a cradle of wire. The grouting was sloshed over the top, resulting in a roof that looked like a flat slab with regular vertical ridges where the wire ran up and over.

It was simple but not terribly effective. Every few years another load of wire and cement was tied and sloshed over the top, and the grouted roof became a common sight. An annual coat of limewash over the cement gave the roofs a brilliant white appearance, and a thousand picture postcards were born.

However, after a few decades of repeated grouting, the roofs became dangerously weak from the sheer mass of cement, while the barbed wire inside crumbled away. It was an object lesson in the folly of short-term, penny-pinching repair, but the look was established as unique to Pembrokeshire; the grouted roof had become a part of the vernacular and was ‘authentic’.

So when Griff wanted a new roof for his barn conversion, it had to be a grouted roof. Forget the fact that a new slated roof would have decades of healthy life in it before any repair became necessary, forget the fact that grouting a brand new roof in the name of ‘authenticity’ is about as absurd as taking a healthy child to a Victorian reenactment and breaking its legs to give the appearance of rickets. Forget even the fact that grouting was done with cement and barbed wire in a desperate attempt to save money and defer proper repairs; the roof had to look ‘authentic’.

Of course, being a conservation project, cement was out of the question – the roof had to be grouted with lime. Modern hydraulic lime, at that. The fact that roofs were never grouted with lime, and that hydraulic lime was pretty much an alien material in West Wales until the end of the 20th century clearly didn’t register.

In theory, however, it should have worked. After all, grouting the roof in lime, trowelled on in three, keyed coats like any other render, is little different to rendering an upright wall in hydraulic lime. It didn’t work, however. The coats delaminated, the lime failed to carbonate properly and large sheets of render/grout came slipping down over the eaves.

It all made for great car-crash TV. Cue the anxious pieces-to-camera and the scramble to allocate blame. After all, the fault must lie somewhere, and none of those involved in specifying or applying the stuff was going to say, “It’s a fair cop, I got that wrong – the whole thing was a daft mistake.”

From the view of a detached observer – me – it appeared that the workmanship was at fault. Lime, even hydraulic lime, needs to be kept damp and away from direct sunlight and wind to cure fully. Each coat needs to be applied to a damp background if the suction isn’t to strip the water out of the render before it can go off. If it dries too fast the lime won’t bond to the aggregate and will simply crumble. If it’s worked to hard with a steel trowel the mix will start to change, with the lime coming to the surface leaving a layer of sand underneath which won’t key to the underlying coat, however well scratched it is.

All of that, it appears to me, seems to have happened on the roof at Strumble Head. I’ve seen it happen on walls before – lack of wetting, inappropriate trowelling and no protection gives exactly the result seen on Griff’s roof. But no – the builder insisted that somehow the lime was to blame. It had somehow failed to do its job, and the allegation was broadcast in the television programme.

For 90 per cent of the viewers it probably meant little; just another hiccup in a make-over programme, and don’t we all love dramas?

But the allegation was important because it would seem to be unfounded and highly damaging to the hard-won reputations of the two companies involved in its supply. The lime came from Ty Mawr in Brecon, a company which has done more than any other in Wales to promote proper practice in the conservation and repair of traditional buildings. Ty Mawr runs courses for anyone interested in learning how to use lime, and will give advice on site as to how to overcome problems. It sources its lime from Singleton Birch in Lincolnshire, a company which has been making lime since 1815, and which makes thousands of tons of the stuff every year. I use their hydraulic lime and it’s the best you can buy; kilned from chalk to give a lime which makes a soft, very sticky mortar and render which cures beautifully. Beautifully, that is, if you know how to treat it properly.

Both companies were effectively defamed by the allegation that they supplied ‘dodgy’ materials. Word spread. On the grapevine there were mutterings that Singleton Birch lime wasn’t up to standard, that it didn’t ‘go off’ properly. There were mutterings that Ty Mawr must have questionable quality control.

For Singleton Birch the episode was an annoyance – the company supplies tens of thousands of tons of lime to the steel and civil engineering industries each year, and the building limes branch is but a tiny part of its operations.
For Ty Mawr, however, the episode was devastating. Here was a company which had built an enviable reputation on supplying the highest quality materials and the expertise to use them to the best, and on national television it was being accused of delivery sub-standard stuff.

Sadly sides have been taken and battle-lines drawn up. There are those on the side of the builder at Strumble Head who now refuse to use Singleton Birch lime and who will not order from Ty Mawr. They cannot accept that there is nothing wrong with the lime that was supplied - a fact proven by expensive analysis of some of the failed grouting, which shows that the lime supplied was perfectly fit for purpose.

Interestingly, I understand that the analysis did show that some gypsum appeared to have been added to the mix. Gypsum – a constituent of modern skim plaster – is sometimes gauged in with lime plasters for indoor use to help them set quicker with less shrinkage. It should only be used in a situation where the plaster will remain completely dry once it has carbonated. If a plaster gauged with gypsum gets wet it will start to break down. It should never be used for an external render. Ever.

It goes without saying that there is no gypsum in Singleton Birch lime when it’s put into its sealed bags in Lincolnshire.

The television programme was broadcast over a year ago, and the rumbles from Strumble are still being heard around the Building Limes Forum and beyond.
Ty Mawr can’t afford to go to court to fight an expensive defamation action, and Singleton Birch hasn’t been hit hard enough to warrant consulting m’learned friends, but the affair is an object lesson in the cost of careless talk.

1 comment:

  1. A comprehensive account of a sad situation.

    Have you thought about asking for this to be published in SPAB's Cornerstone?