Aspecialform of denser bog peat, called rose-peat, has often been used asthe sealing material in dams. At the silver mines of Kongsberg in central Norway, dams of this peat are still watertight after being in usefor 150 years. It is probably also suitable as a moisture barrier for foundation walls. Its sealing ability is due to the fact that it can absorb and hold large quantities of water.
The rose-peat, which is dark brown and available in most bogs, consists mainly of rotten leaves, and is found below the level of the roots in the bog.The plant fibres have to be visible, but the structure broken down. When a piece is rubbed between the fingers, it leaves a thickfatty layer on the skin, like butter. If the peat contains enough fibre, it feels rough. If it contains too little fibre, it feels smooth, like soap.The peat is cut out in cubes of12 x 12 x 12 cm, often going down several layers before water fillsthehole.
The rose peat must not dry out and should be used as quickly as possible, but its properties can be preservedfor upto a weekin damp weather by covering it with leaves and pine needles. Its use must be limited to frost free situations.
Peat matting consists of peat fibres sewn between layers of paper.
Peat boards are made in thicknesses of 20-170 mm. Their properties as a thermal insulation are very good, and can compete with mineral wool or cellulose fibre. The most widespread method of production begins with the peat being taken to a drying plant where it is mixed in warm water (Figure 14.25). It is then removed from the water, which is allowed to run off, leaving a moisture content of 87 to 90%. The mass is then put into a mould in a drying kiln to dry to 4 to 5%. To achieve different densities, different pressures can be applied. The whole process takes about 30 hours.
Pressing peat slabs using the wet production method. Source: Brannstrmetal.1985.
A dry production method can also be used. The peat is then pressed directly into moulds so that the damp is driven out of it. By warming it to 120-1 50 °C with no air, its own binders and impregnating substances are released. This is equivalent to its charring temperature, so the boards become fire resistant. There is also no need for added binders. This dry method of pressing came into use between 1935 and 1940 in the former Soviet Union. The method requires a relatively large amount of energy for the drying and setting processes, but this can be reduced to a certain extent by using solar energy for preheating.
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