the furnace as a spongy mass which was filled with unwanted impurities, these were worked (wrought) out by hand to produce wrought iron. Carrstone quarries Historically, there have been numerous carrstone quarries along the Carrstone belt. Snettisham Carrstone quarry in Norfolk is still active and produces high iron content building stone. Conservation of carrstone buildings Carrstone, as with many other building stones, is vulnerable to decay. There are many factors which influence the life of carr building stone such as the bedding mortar, moisture control and orientation of stone. Appearance of carr building stone can also be affected by factors such as mortar colour, mortar inclusions, stone shade, orientation in the wall, galletting and shapes of stone. Construction methods Carrstone can be used in much the same way as any other building stone, but with the disadvantages of friability and of being more difficult to cut by hand. Whilst the stone is used as a single leaf for newbuild to reflect the more vernacular buildings, it is more common to see traditional methods of construction which involve an inner and outer leaf with a rubble core fill. This type of wall is referred to as 'solid wall construction', but this is a misleading description due to the two leaves and core fill having different properties from a true solid wall, which is more susceptible to condensation and other damp mechanisms such as penetrating and rising damp. References Sandstone