Sunday, 20 October 2013

Flying High

I am suffering from project grief.

Mercury, Pegasus House (D. Dunlop)

If you've read previous posts here, you will know how I have been head-over-heels in love with a number of badly-abused Art Deco plaster panels.  Fully restored and re-instated to their full glory at Pegasus House, Bristol, I've had to let them go.

Airbus, the company which have taken over use of the building and funded its restoration, held a fantastic opening party to celebrate the work carried out and to toast a new era of aviation at Filton.

The event was such great fun: 1930s themed with fancy-dress, a swing-band and barber-shop quartet, peach iced-teas and flying-saucers, vintage cars and planes, and a seriously impressive ice-sculpture! Throughout the day, groups were taken through the building and the various conservators spoke about their role in the restoration. (I was delighted by this: groups of twenty or so people that HAD to listen to me gush about these panels! What luck!)
Aside from this, it was great to see the rest of the conservation work undertaken. In particular, the restoration of the Jan Juta, Mercury and Pegasus window  by Creative Glass was superb.

This building has truly emerged a phoenix from the flames and it has been such an honour to play the tiniest part in it's revival.

Pegasus and Mercury window, Jan Juta 

Installing the panels in the projection room (AK)
The panel I worked on - very proud!
Hot-air Balloon Before & After

Townscape Before & After

The following images are courtesy of Airbus:

In the beginning...
Zodiac mosaic to entrance hall

A fall from Pegasus is a long way down, but luckily, I had the Fitzrovia mural waiting to pick me up again...

Fitzrovia Mural

The mural was commissioned by Camden Council in 1980 and, following community discussion, it was decided that the artwork would show scenes of local life, including portraits of local people, and would be painted entirely in household emulsion paint. Designed by artists Mike Jones and Simon Barber, the Fitzrovia Mural is of immense cultural and artistic significance, and is one of the few major murals painted in the 1980s to remain largely intact.

One glance at the artwork would tell you it was in poor health: the drained colour, the multiple fractures and blisters being just the beginning. 

While the defects were obvious during the survey, the reasons for them was not apparent to me until back at the office with the drawings laid out and the pattern of deterioration studied. 

The mural is painted on cement render to the gable-end of a Victorian brick building, just off Tottenham Court Road; the building appears well-maintained with sufficient rainwater goods. 
The render appeared to be quite unevenly applied with varying surface textures and thicknesses.

In rougher surface areas, aggregate in the mix appears to have been brought to the surface in clusters, perhaps as a result of over-trowelling; in others, the uneven surface is due to blisters in the render, many of which have burst, resulting in spots of paint loss. These blisters may have been formed by bubbles of air migrating through the render and becoming trapped under the surface. This may be due to accelerated evaporation on the exposed surface.

Failed mastic repair
A number of hollow areas were noted, indicating delamination, but the movement of the render in these areas was minimal. However, moisture will penetrate through any cracks in the render and the constant freeze-thaw cycle of expansion and contraction will cause these hollow voids to grow and could eventually result in the render being 'blown' off the wall.

Cracking is formed by a network of horizontal fractures across the entire surface, which become more prominent towards the lower section. This pattern of deterioration is likely to be caused by water penetration and saturation of the underlying brick substrate leading to salt-leaching. The subsequent expansion of the mortar joints results in pronounced horizontal cracking. Use of an overly-strong render which shrinks and cracks as it dries, opens the coating to water ingress.

Horizontal fractures following line of joint

AW and RM
Inherently, a large expanse of exposed render will be subject to daily and seasonal expansion and contraction cycles. As cement render is hard, brittle and impervious to the stresses of thermal expansion, any stresses will break through at these weakened points, opening the render to further water ingress. This problem is exacerbated by the lack of slip joints.

Once formed, these fractures allow water to penetrate the render. As cement is impermeable, it does not allow for ready evaporation of this moisture. Freeze-thaw action causes these fractures to widen and deepen, eventually creating hollow areas, where the render has delaminated from the brick substrate.

Furthermore, differential rates of evaporation and thermal expansion between the brickwork and cement will cause stresses to develop, which will serve to worsen fractures and hollow pockets.

Another point of concern, the gable the mural is painted on to is topped with a FIFTEEN pot chimney stack! The flues running within this wall could, historically, as it is believed they are no longer in use, have exacerbated issues of thermal expansion by creating steep thermal gradients. Products of combustion could also have caused historical sulphate deformation.
(FYI: All pots are now capped.)

Biological growth along fracture indicating moisture retention 
In addition, there are a few minor areas where fine fractures, or map crazing, have broken across the surface of the render.  These are caused by over-trowelling the mix, leading to a thin film of water/cement paste forming on the surface. This forms a network of tiny hairline cracks as the render dries.  These cause minor, low-level distress and while they do not affect the structural integrity of the render, they do compromise the paint surface.

(Boy, do I love this type of thing! This book was an excellent resource for identifying the issues with the render.)

Deep fracture with paint curling away along line

As mentioned, the paint-system is domestic emulsion paint, and this has weathered very badly over the past 33 years, due to exposure to elements and urban pollution. While modern paints have UV filters to prevent, or at least delay, pigment degradation, unfortunately, there is no way of restoring colour and vibrancy to the painting.

White colour-field
prone to cracking
There are a number of paint losses across the surface owing to different  factors;  paint is seen curling away at the site of fractures due to differential expansion rates between the paint-film and the render, larger losses along fracture lines are likely to be due to issues with moisture ingress, some areas exhibit salt blisters which have ruptured through the surface, taking paint with them, and some colour-fields have experienced accelerated deterioration, resulting in severe cracking and flaking.
Cleaning tests to remove the extensive graffiti were not successful, as there was an insufficient margin of safety between the solubility parameters of the original and non-original paint.

Burst blisters resulting in paint loss
Large, isolated loss at fracture
Flaking paint and subsequent losses

Finally, there is significant biological growth across the surface. Of course the thick vegetation at the base and winding up the service pipe aren't helping matters, but also, dark mould is seen around paint flakes and powdery lichen is dusted across the mural.

I had always thought lichen, with their bacteria-algae symbiosis were pretty cool, but whilst trying to learn more about the biological growths at Fitzrovia, I discovered even more fascinating things about them - like, how the colour and type of lichen in an area can tell you about air pollution levels and how a Dutch Biodiversity Centre uses lichen to 'pigment' concrete buildings!

Considering the issues with this artwork, restoration and conservation treatment options are limited, and are still under discussion at this point.

There are some wonderful images in this mural, some of which I've included below:


Dr Lynn Pearson has produced lots of good stuff on postwar murals in Britain and Ireland, including a field-guide and database. She works in conjunction with the Twentieth Century Society on their Murals Campaign.

Over the past few weeks, I've been keeping my head down, investigating the paint failure at the Brunswick Estate, Hove, which I touched on in an earlier post. This work has, on occasion, caused me to tear my hair out, but thankfully, it is coming together nicely. There are lots of juicy things to talk about, but I will leave all of that till the project is over and I can talk about it in depth. In the meantime, here's a rather jazzy-looking photomicrograph from the paint analysis. (Algae turns red in UV light; cool, huh?!)

In visible and UV light

As a very final note, as this as become an epic post, recently I was lucky enough to hear Ptolemy Dean give the Churches Conservation Trust annual lecture on his work at St Margaret of Antioch, Knotting, Bedford. His talk was tremendously entertaining and hugely insightful into his conservation approach. He ended the evening talking about project grief - the sadness felt at the end of one of those jobs that really gets under your skin...

Lemon and Lime

In September, I travelled to Rochdale Town Hall, Lancashire, which is an astonishing Grade I listed, Gothic Revival masterpiece. It is beautifully decorated with banded stone lierne-vaulting to the entrance Exchange supported by thick marble columns topped with wreaths of ferns and foxgloves, horse-chestnut leaves and rowan-berries, oak leaves and roses (to name but a few - each capital is different!), each with a little creature pecking amongst, dozing or watching from the foliage. Vibrant Royal Arms mosaics pave the floor leading to the sweeping staircase. At the top of this, a full-length stained-glass window drenches the room with dappled light, drawing the visitor up the steps to the magnificent Great Hall.

Vaulting and Columns

Our work was in the Exchange Hall, where the figurative and naturalistic stone carving had become badly chipped and damaged. Of course, it is not realistic or reasonable to recreate every chipped edge, so our work involved remedying larger disfigurations and replacing any visually-detracting losses and defects.

At this, the outset, our task was to identify the most effective and efficient modes of recreation, be it taking moulds of existing decorations, casting and mounting, or installing armatures and hand-modelling details. We also needed to determine the most suitable mix: basic lime mortar or acrylic-composite mix. To this end, we began to make moulds of the decorations by trialling different resins; we needed one which was plastic enough, so that it could easily be applied to pick up intricate detail, and elastic enough so that it could be readily removed and manipulated to cast from, but also robust enough to withstand numerous castings. While these were setting, different mortar biscuits were prepared, with adjusted pigment ratios to match the existing stone colour as closely as possible, as well as mimicking texture and hardness.

While good in theory, in practice the mould-making approach was a bit of a lemon: Vast amounts of time were spent casting, drying, shaping and installing moulded elements, so in the end, freehand modelling in lime, which complemented the limestone carvings, was found to be the fastest and most effective repair.

The pictures below show the processes.

Impost, showing missing decoration on RHS

Mortar biscuits for colour, texture and hardness testing

Taking moulds of decoration with cast and finished piece to right
Mould made using more pliable resin requiring reinforcing plaster case
Armature fixed to crown and detail modelled free-hand in pigmented lime mortar

Crown tips rebuilt

From here, I travelled a little further afield, to Dublin, for the Building Limes Forum Ireland conference. Held in the stately setting of Kings Inns, this was a shameless three-day lime binge.
There were some fantastic lectures, covering Irish brickwork and pointing techniques, extolling the sustainable virtues of lime, lime-hemp, lime-crete and friends, and stucco-work and its repair to name just a few.

As a proud Corkonian, the weekend was a little Dublin-centric for my taste; yet, despite this, it was fascinating to learn about the development of Georgian architecture in the city, how it drew reference from grand London terraces and squares, yet had a distinct local accent, particularly with the lack of ornament and the boulevard-type streets. (This is due to the Street Widening Act (1720) of which there is no British equivalent.)

I love old brick - the production, colour, romance - so, needless to say, I loved Susan Roundtree and Gráinne Shaffrey's lectures on brickwork and pointing in 18th century Dublin, as well as their tour through the city.

Henrietta Street
(Excluding the carved door-cases, these could almost be taken as having a minimalist, Modernist influence

Henrietta Street, built between 1729 and 1758 and designed by James Gandon, was right on our doorstep and provided examples of everything touched on in these talks. Most of the properties on this street are terribly run-down and many are abandoned. Although, in recent years its significance has been recognised and Dublin City Council have driven forward with its repair and conservation.

Extent of decay at Henrietta Street

Susan and Gráinne took us through the history of brick-making and brick-laying in Dublin. Particularly interesting was the discussion on different styles of pointing, of which there appears to be a unique style, known as 'wigging', in Ireland. Wigging is possibly a derivation of bastard-tuck pointing, where the tuck  may have been formed as a ribbon and inserted or formed of the pointing mortar. Remaining exposed mortar (bedding or pointing)was filled in using a coloured mortar, leaving the impression of an ultra-fine joint. The image below explains this pretty clearly, I think.

Susan Roundtree lectured on the architectural conservation course I studied in Dublin and is definitely responsible for my love of brickwork. Both she and Gráinne have worked on this guide to Repair of Historic Brickwork, which is wonderful and everyone should have a copy of. 

While there is so much I could tell you about, I'll just talk about one more topic that was covered, The Dublin School of Stuccowork. Frank Keohane began by  explaining how despite the unadorned facades, the interiors of Dublin townhouses boast some of the richest and most elaborate stucco in all of Europe, showing examples of work by the LaFranchini brothers and Robert West. He also told of how Irish stuccodores avoided figurative (human) modelling, favouring naturalistic, as they lacked the formal, classical training followed by their European contemporaries. Any examples of human form were generally ungainly and, compared to the rest of their work, lacked accomplishment. From here, Conor Lucey went on to tell about the materials and methods of stuccowork, highlighting how about one quarter of the city's 18th century stuccowork has been lost due to ignorance and carelessness. 

Finally, Richard Ireland led us through some of the plaster conservation projects he has carried out in city, looking at decay mechanisms and modes of repair. In the afternoon, some of us were lucky enough to go with Richard to 20 Dominick Street; a five-bay townhouse designed by Robert West, housing some very flamboyant plasterwork. Richard restored the plaster and paint-systems throughout this interior, and it was great to hear his account of the work firsthand. The following are just some examples of the stuccowork at Dominick Street.

Finally, this is a nice article on the conservation of decorative plasterwork from an Irish viewpoint. These Richard Ireland articles on cleaning and conserving decorative plaster are excellent, and of course, no mention of building lime in Ireland go without mentioning Lime Works.