2. Slate
Slate s a stratified metamorphic rock and is
obtained from open quarries. It is the finest
grained foliated metamorphic rock.
Many slates will form smooth flat sheets of stone
which have long been used for roofing, floor tiles,
and other purposes.
Slate is mainly composed of the
minerals quartz and muscovite or illite, often along
with biotite, chlorite, hematite, and pyrite and, less
frequently apatite, graphite,kaolinite, magnetite, to
urmaline, or zircon as well as feldspar.
3. Formation of a single tile
•Slates are obtained from
quarries as blocks .
•Reduced to slabs after
dividing into sections using
diamond or circular saw.
•Each slab is divided into
thin laminate or slate by
using splitters.
4. Fixing and laying of slates
Slates roofs tiles are usually
fixed either with nails or with
hooks.
Fixing is typically with double
nails onto timber battens or
nailed directly onto
timbersarking boards.
Nails are made up of alloy and
stainless steel.
5. Laying methods
There are various methods of
fixing a slate .
1.By nailing near the head .
2.By nailing near the middle.
6. Head nailed slates:-
Slate are fixed by means of copper nails driven
through holes which are punched near the head of
each slate . Two holes are punched in each slate
about 25mm from its head and about 40 mm from the
side .The advantage of this slate is that there is two
layers of slates covering the roof so there is no risk of
water getting through holes.
7. Center nailed slates:-
One low pitched roofs, slates are commonly fixed by
center nailing. Nails are not driven exactly in the center
but at a distance towards the head of the slates .
The advantage of this method is that the slates are
firmly held in position because of this less number of
slates are required.
8. COST
25-30/Sq.ft
Quality of a good slate
•It should be free from white patches , hard, tough
durable and give a sharp metallic ringing sound when
struck with each other.
•It should be easily holed.
•It should not split and absorb water more than 2% of
its weight when soaked for 24 hours.
Size
Common sizes are 600*300 mm,500*250 mm and
450*200 mm
9. The Pros
Appearance
variation in sizes and colors give aesthetic appearance.
Fire Resistance
Slate roofing is one of the most fire resistant roofs that
exist
Longevity
It needs less maintenance and runs for almost 20-30
years.
The Cons
Weight
The weight of slate roofing tile is anywhere between 800
and 1,500 pounds per square (100 square feet). So it is
necessary to built a structure that can bear its over all
weight
