Public Places
of years, has worked on many English Heritage sites. The five man team is headed up by Kristan Short who oversaw the month long project at Hailes Abbey which was completed in March of this year.
At the time of my visit in late February, eighty percent of the work had been completed, so I was able to see for myself the scale of the work involved. The project, which is expected to cost around £50,000, will help preserve the ancient ruins.
The concept is relatively straightforward and involves the laying of harvested natural turf over a layer of loam soil placed on top of the walls and structures to be protected. This natural layer effectively acts as a thermal blanket, reducing the effects of frost damage. One of the biggest costs is the erection of scaffolding to access the walls, plus the fact that all materials have to be walked onto the extensive site using wheelbarrows. Alan now explains the process and benefits of soft capping. “It is important to remember that all of the old castles, abbeys and other historic buildings we now see as ruins in the landscape were once fully functional buildings, with a distinct inside and outside and a roof over the top. They were certainly not designed to be open to the elements from every direction, and the deterioration problems which occur
are a direct result of this.
The two principle causes of fabric deterioration on ruins are the ‘Freeze/Thaw Cycle’ and the ‘Wet/Dry Cycle’.
Freeze/Thaw Cycle - when water
freezes, it expands in volume by 9%. If this water is in the surface layers of stone - particularly porous limestone and sandstone - this expansion can cause the surface layers of the stone to break off, a process termed ‘spalling’. If entire blocks of stone are soaked, it is possible for the whole block to shatter. Wet/Dry Cycle - Porous stone can hold water within its structure, especially if it is open to the elements during wet periods. Then, just like plants, stones can lose water when the weather is dry and, again like plants, particularly when it is breezy. Water evaporates from the surface of the stone, and water within the stone matrix is ‘sucked’ to the surface to be lost in turn. Some stones contain various mineral salts, and these can be dissolved into solution if the stone is soaked, travel to the surface of the stone and then, as the water is evaporated, they come out of solution. This sometimes happens at the surface and shows up as a white crusting on the stone, but it can also happen just below the surface. Some salts can expand in volume by 40% or more as they come out of solution, which can cause spalling even worse than that caused by frost. From the turn of the 20th Century (but
particularly from the 1920s onwards), many historic sites were excavated and opened to the public. The belief, at the time, was that all vegetation was bad for the stonework (not to mention untidy!) and was, subsequently, stripped off and replaced by ‘hard capping’ - wall tops made from hard, cementaceous mortar designed to shed water as quickly as possible.
This work was done with the best possible intentions but, by the 1990s, it was clear that fabric deterioration was not being slowed and, in many cases, appeared to be accelerating. Looking closely at these problems, it became apparent that hard capping was not improving the situation and actually seemed to be making it worse because; - Hard caps always cracked, often within a few years of installation, and even hairline fractures allowed water to penetrate into the core of the wall. Once in the core, water took the easiest way out. This should have been the mortar joints (lime mortar allows some water movement) but, along with hard caps, many monuments had been repointed with hard cement mortar and, so, the water was forced out through the stones exacerbating the problem cycles described above
- Hard caps gave the stonework
“It is important to remember that all of the old castles, abbeys and other historic buildings we now see as ruins in the landscape were once fully functional buildings”
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