Civil Engineering Reference
In-Depth Information
Certain types of stone contain quartz and dust can be a risk during the work-
ing of the stone (see Table 7.3). Slate, limestone and marble have low radioactiv-
ity and therefore are no problem for the indoor climate. Certain types of granite
can present a problem as a source of radon gas.
Stone floors are easily looked after, durable and resistant to spillage of water
and other liquids, depending upon which stone is used. Marble cannot be used
in men's toilets as it reacts with urine. Stone floors are hard and cold to walk on,
unless floor heating is used.
Slate and stone tiles laid in a weak mortar can usually be taken up and re-used.
Stone products that are fixed mechanically are easily re-usable. Over 90 per cent
of the slates from an old roof can usually be re-used. It is necessary to ensure that
they are high quality and not very porous with a high content of calcium car-
bonate. There is also a difference between stone that comes from coastal or inland
regions. A coastal slate has usually been exposed to a more severe climate, with
frequent changes between frost and mild weather. The same applies to stone tiles
which contain lime or sandstone and have been exposed to a severe climate as
wall cladding; these are not so easily re-used. All stone should therefore be care-
fully checked before re-use for strength and porosity. Dumping stone waste is
seldom a problem.
Practical use of stone surface materials
Roof covering
Before laying, slate tiles are sorted into two, three or four groups of different thicknesses,
unless this has already been done at the quarry. There is usually a timber board roof with
felt on, if the roof is to be windproof, otherwise the felt can be left off. The slates are fixed
onto battens, unless the site is very exposed to wind, when they are fixed directly onto the
boarding.
The usual size of the battens is 25 50 mm. The distance between the battens depends
upon the method of laying, the type of slate and its form, but mainly on the distance between
the lower edge of the slate to the nail holes, minus the overlap.
The thickest slate is laid furthest down on the roof, to avoid large variations in thickness
on the other courses. A slate hammer is used to split and shape the tiles. When breaking
the corners, a special tool fixed to a wooden stump is used. The tiles are fixed with spe-
cial slate nails which are 25/35 mm, 28/45 mm and 28/55 mm. The ridge is covered with
rectangular slate tiles, timber boarding, zinc, copper or even turf.
Rough tiles
When laying rough tiles, holes are first bored or hacked in the tile with a drill or a special
hammer. The tile is fixed to the batten with a strong galvanized nail or a slate tack. For
large tiles wooden pegs made of ash or juniper can be used. As rough tiles do not always
lie tightly on each other, they can be broken by heavy snow loads. One way of resolving
this problem is to put lumps of clay under the end of each tile. If time is spent sorting the
