C O N T E X T 1 2 3 : M A R C H 2 0 1 2 9 Supporting Columns Controlling decay at Plas Coch Robert Demaus discusses how understanding the widely feared, and misleadingly termed, dry rot benefited an ambitious conservation project at a gentry house in North Wales. and sometimes perhaps wilfully, misidentified as ‘dry rot’. A recently completed project inAnglesey demonstrates that an alternative to the conventional approach of radical surgery and extensive chemical treatment can result in very significant savings, both in terms of costs and historic fabric. Plas Coch is a substantial Grade II* 16th century gentry house overlooking the Menai Straits in North Wales. Like many such houses, its fortunes have varied. By the end of the 20th century it had suffered frommany years of neglect, with little or no maintenance.What little work that had been done, such as cementitious ribbon pointing, had simply made matters worse. When new owners took over, they required an exemplary restoration of the house to form the heart of an exclusive holiday venue. To this end, they appointed Donald Insall and Associates to oversee repairs to the house and the creation of new facilities. They in turn asked me to carry out a detailed survey of the building to identify the various agents of decay present, assess the extent of degradation caused, and prepare proposals for remediation. First impressions were not good. Holes in the roof, broken roof-lights, missing flashings and no effective guttering allowed water to penetrate many areas of the house, particularly in the upper floors.The combination of projecting cementitious pointing externally (intended to prevent water entering the walls), and some modern non-breathing internal finishes, prevented any evaporation from the walls. Unsurprisingly, a variety of decay mechanisms had taken hold.The most significant were the brown rots Serpula lacrymans and ‘cellar fungus’ (Coniophora puteana). There were also less significant outbreaks of white rots (Phellinus contiguus andDonkioporia expansa), and some relatively minor furniture beetle(Anobium punctatum) in softwood elements. In some areas, floor structures were too degraded to walk on. As there had been so much water penetration through the roof, zones of decay were not confined to external walls. Mortar pugging, used as sound insulation between floors, created substantial reservoirs of moisture, exacerbating the problem. Of the many problems, real and imagined, that can beset owners and carers of old buildings, ‘dry rot’ is perhaps the most dreaded. It is often described as a ‘cancer’ that can spread through a building at an alarming rate, and much of the imagery and language used reinforces this notion. Why has this particular fungus achieved such notoriety, and is its fearsome reputation justified? There is no doubt that ‘dry rot’ can cause extensive damage, but like so many bêtes noires, the fear generated is often disproportionate to the damage caused. A multi-million pound industry sustains those fears, and has worked hard to maintain them, ably assisted by celebrity self-styled ‘conservation superheroes’ intent on making exciting television programmes. Sadly, all too many building professionals remain in ignorant awe of the fearsome beast and the myths that surround it. Even the very term ‘dry rot’ is misleading. It first appeared in the late 18th century, originating from a fundamental misunderstanding of the differences between what should be termed white rots and brown rots.White rots generally leave a stringy mass of spongy fibres that was thought to be caused by excess moisture. These were called ‘wet rots’.The brown rots, by contrast, degraded the wood to form cuboidal cracking (a bit like parched earth) and a crumbly texture, often leaving an undamaged outer surface, which it was thought could not be caused by excessive moisture, and must therefore be due to ‘fermentation of the juices of the tree’ and/or heat.These were therefore termed ‘dry rots’. Over the ensuing 200 years, the term ‘dry rot’ has become restricted to just one fungus – Serpula lacrymans, with all other wood-decaying fungi grouped together as wet rots. Nonetheless, the term itself is a misnomer which continues to cause confusion: all fungi must have a local source of moisture, and will die if that moisture source is removed. Serpula lacrymans is no different, but somehow the notion that it is uniquely capable of surviving and spreading far away from a source of water persists, even among those who should know better.To make matters worse, more commonly found brown rots, such as ‘cellar fungus’ (Coniophora puteana), which can do as much damage, but do not have the scare factor, are routinely, Left: Plas Coch, a magnificent 16th century gentry house in Anglesey, has been rescued from severe decay and restored to its former glory. Right:The projecting cementitious pointing trapped moisture in the wall and reduced evaporation, quite apart from being unspeakably ugly.
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