Revolution in wall design?
Some things in life remain constant, no matter what happens to other products around it. Aircraft chocks have always remained the same, no matter what size the aircraft is. Wheels are always round otherwise they would not function. Almost always, rooms have four walls. It has to be that way, so that the structure can support a roof. Walls have several other functions, for instance they provide protection from the elements, security, they also have to look attractive. Increasingly they also have to provide thermal insulation, thus allowing us to modify our internal environment, ie keeping us warm in the winter and cool in the summer.
It is the last quality that is becoming increasingly more important, particularly as we try and stop the march towards global warming. Wall design has moved over the centuries, as building technologies have improved. We have come a long way from the first caves, to wooden shelters. Timber was the first major material to be used, and there are still many examples of the oak framed black and white properties around to prove their durability. Originally the infill panels were daub and wattle with a mixture of clay, cow dung and straw hand mixed and applied by hand to a lightweight wooden frame. Then builders moved onto baked clay brick for an infill material, they found that clay bricks were more durable and predictable to use.
In building design terms one of the big events took place in 1666, when the great fire of London occurred. Suddenly all the weaknesses of design were exposed, as great swaths of buildings disappeared into ash. Parliament started to provide regulations covering building design, the party wall act etc. Bricks were increasingly used as the main form of material, to construct a wall with, they didn’t burn, and could support immense weights allowing larger and higher buildings to be constructed.
At first all bricks were hand made, a slow laborious task at the best of times. In about 1850, the Victorians started to mechanise brick construction, the standard sized brick was created, 9” X 4 1/ 2” X 3”. The supply of timber was shortening, and becoming more expensive. At the same time, bricks were becoming more affordable, and predictably available, which resulted in their use becoming much more widespread. At first the external walls were double thickness, using patterns such as English Bond, and Flemish Bond. As ever there were variations on a theme, such as Rat Trap Bond and English Cross Bond, and architects made extensive use of variations in colour of bricks in an attempt to make brick walls more architecturally attractive.
One of the big problems with this design was that during periods of heavy rainfall, the external porous bricks would allow water to be absorbed. If enough water soaked in, damp would eventually show through to the internal surface of the wall. Hopefully there would be enough evaporation-taking place to allow the internal surfaces to remain dry. During the early days, a lime based plaster was used, which again was porous in nature, thereby allowing free movement of moisture in and out of the wall.
The next big jump in wall design was the development of the Cavity Brick Wall. First seen in the early 1930’s, the idea of the cavity wall is that two brick walls are built parallel to each other. They are tied together by inserting wall ties in the mortar beds. At first these ties were made of steel, but as people realised that this would lead to corrosion problems, increasing use was made of alternative materials such as galvanised steel, stainless steel, and plastic. Over the decades, the cavity gap has been increased, to allow for insertion of insulation products between the walls. Wall tie design has also been improved, to ensure that any moisture soaking through the outer wall runs down the inside of the outer wall of the cavity, and out at the base of the wall.
Over the years, the system has proved to be extremely durable, early wall ties have failed in some instances, resulting in the collapse of the outer wall, but as ever where a problem is known about technology has stepped in with a cure, the glue in replacement wall tie, and life carries on as normal. Where in some instances, the outer wall has fallen away from the property it has been re-built relatively easily.
One of the perceived problems with cavity walls, is as ever the speed of construction. One can only build so high in one day, before leaving the wall for the night to allow the mortar to set. Brick- laying is also a very skilled job, it takes years for a bricklayer to learn his trade, and the end product’s appearance is very dependant on the skill of the brick-layer.
As ever, technology will always attempt to design a new system in an attempt to drive costs out of the build process, and achieve a better uniformity across the end result. I came across a new clay block system, marketed by Natural Building Technologies Ltd., that attempts to do away with the traditional brick wall, replacing it with an extruded clay block, which has vertical perforations and whose trade name is “Thermoplan”.
During the manufacturing process, sawdust is mixed in with the clay, when the block is fired in a kiln, the sawdust burns off to leave porous holes, without losing strength in the clay block. The blocks are then laid on a thin bed of mortar approximately 1mm thick, which is actually laid using a machine. Because there is so little mortar present, the mortar dries out extremely quickly, thus allowing block laying to continue without the usual delay of waiting for the mortar beds to set. The manufacture claims that construction times are speeded up by approximately 4 times, when compared to conventional construction techniques.
Externally the finish is not as attractive as a fair- faced brick, and obviously the clay block is extremely porous. In order to finish the outer surface, the wall is cement rendered, this actually provides the weathering surface, which repels the worst of the weather. Because so little mortar is present in the final wall, shrinkage and expansion is also kept to a minimum, thereby minimising cracking.
It will be interesting to see over time how quickly this build system becomes introduced, and how durable it will prove to be in the long term. I was however very surprised to see these blocks being used on a site in Evesham, which might indicate that I have been slow to notice it’s introduction. Anyway, I will continue to watch the build systems progress on the site, and to date I can verify that it does form a very fast system of construction.
Tony Rowland - The Property Doctor!
Timothy Lea and Griffiths Estate Agents
