Diminishing: the system whereby slates
are sorted by length and laid with the longest at the eaves, diminishing
to the smallest at the ridge. It is essential that the minimum head lap
is maintained when there is a change of slate length between two courses.
This also ensures that each successive margin is the same size or smaller
than those below (see pigs).
Double lap: stone slates laid so that
each course overlaps the course next but one below. In some regions and
in some special applications, triple lap slating (where each course overlaps
the course next but two below) is adopted.
Dressing: the process of shaping the
stone slate and producing the edge detail using either a chisel-edged hammer
or a bladed tool. Regional differences exist for the edge detail which
may be square or beveled. Synonyms: trimming, fettling (Yorks, Lancs).
Eaves, of stone slates: the short course
laid at the eaves under the first full course. The method of placing and
supporting the eaves stone slates varies regionally. Synonyms: under eave(s),
Facies: the characteristics
of a sedimentary environment: rock type, mineral and fossil content, sedimentary
and bedding structures.
Fissile: rock which can be split along
Fixings: nails or pegs.
Gallet: small pieces of stone slate
or metamorphic slate bedded in lime mortar at the head of a slate to support
the slate above. Synonym: shale.
Gauge: the spacing of laths or battens
up the roof slope. In stone slating, the gauge is always variable.
Head: the top edge of a stone slate
Head lap: in double
lap slating (the normal method), the amount by which a stone slate overlaps
the stone slate in the course next but one below. In single lap slating
such as diamond pattern it is the amount by which each slate overlaps the
one immediately below.
Heap: (Collyweston) a quantity of dressed
slates of all sizes on the ground. A heap should produce about two squares
of slating laid on the roof and is made up of -
Lath: split wooden support for hanging
stone slates. Synonym: batten. In this guide, the word batten is reserved
for sawn supports.
Log: (Collyweston) a lump of stone of
no defined size quarried for the purpose of making slates.
Margin: strictly the area, but more
commonly the length, of the exposed part of the slate.
the process, involving heat, pressure or both, which changes the direction
in which sedimentary rocks split. Metamorphic rocks such as true slates
split along cleavage planes which are unrelated to their original bedding.
Sometimes the cleavage and bedding are parallel. True slates are formed
by low grade metamorphism - not much heat or pressure involved. Higher
grades of metamorphism produce rocks with larger mineral crystals which
can be seen without magnification. Examples include schists, quartzite
and gneiss. Generally such rocks cannot be split thin enough to use for
roofing, but some examples do exist.
Mossing: use of moss or other vegetable
material to windproof the joints and gaps between stone slates.
Mossing iron: tool used to force moss
etc. between slates.
Overburden: in quarrying: useless
material which overlies a bed of useful material .
Parting: (Collyweston) a set of slates
of the same length.
a quarrying term for any fissile rock. For Cotswolds stone slates it is
used specifically for rock which is split by frosting.
Pig: a course with a longer margin than
the course(s) below resulting from poor setting out and a failure to maintain
an adequate head lap.
Pitch: the angle of the rafters to the
horizontal. The pitch of the stone slates will be significantly less because
they are resting on each other, but this is taken into account by the traditional
rafter pitch and lap relationship for the slate and the locality.
Pointing: use of mortar to fill the
vertical joints and to seal the tail gap of stone slating. Pointing may
show (undesirable) or be raked or held back. Often associated with bedding.
slates formed by natural weathering in near surface deposits. They are
often thicker than hand-split stone slates produced from deeper layers
Pied: (Collyweston) a method of storing
logs during the summer to prevent drying out.
Pit: a mine or quarry for the extraction
of stone or slates.
Random, of stone slate: variable length
Random, of roofing: slates laid with
reducing length up the roof slope and the widths selected and placed so
that they provide at least the minimum side lap over the slates in the
Regularly (of diminishing or random
slating): the system whereby each successive margin is the same size or
smaller than those below. It does not mean that there are an equal number
of courses of each margin size.
rocks which have been formed from other rocks which have been broken down
by weathering, or rocks formed by biological or chemical actions. If they
can be split to make roofing (fissile) it will be along bedding planes.
Shadow: a thin
piece of slate used in the Horsham district to improve the weather resistance
of the roofs when, because of a shortage of stone slate, the head lap is
reduced to less than the normal minimum. Originally the shadow was a thin
piece of Horsham stone but it is now normally a Welsh slate. It was
always used in conjunction with mortar bedding and pointing. Technically
this is an undesirable method, however it has been in use for about 100
years and appears to work satisfactorily.
Shale: small pieces of stone slate or
metamorphic slate bedded in lime mortar at the head of a slate to support
the slate above. Synonym: gallet.
to remove the top corners of a stone slate; (n) the top corners of stone
slates. Excessive shouldering can result in a leaking roof.
Side lap: the lateral amount by which
a slate overlaps the slate in the course below.
Slate: People have
different preferences for terms to describe sandstone, limestone and similar
non-metamorphic roofing products. The most frequently encountered, traditional
and colloquial terms are stone slates or grey slates but they are also
called flags, flagstones, thackstones, stone tiles, sclaites or grey sclaites
(in Scotland), slats or slatts. Each of these terms is used to distinguish
them from metamorphic, Welsh or 'blue' slates. The objection to the term
stone slate is that sandstones and limestones are not, petrographically,
slates. That is, they have not been metamorphosed and consequently they
split along bedding rather than cleavage planes. This is certainly true
and some geologists prefer the retronym tilestone to distinguish them from
real slates. However the term slate, meaning any 'flat rectangular' roofing
product has historical precedence, since it predates the science of geology
by hundreds of years and is the term in common use. In this website we
use 'stone slates' for preference but in geological pages 'tilestones'
will be encountered and don't be surprised if you find any of the other
synonyms. If this is confusing, the easiest thing to remember is that metamorphic
slates will always be called ......... metamorphic slates! Anything else
Sprocket: the lower pitch of the roof
slope at the eaves; the additional piece of rafter fixed to the main rafter
to give the tilt at the eaves. The sprocket can arise naturally due to
the rafter footing on the inner face of the wall or can be deliberately
constructed to carry the eaves away from the outer face.
Square: one hundred
square feet of slating laid on the roof.
Tail: the bottom edge of a stone slate
Tiering: see torching.
Tilt: the lift provided to the tail
of the eaves course to ensure that successive courses lie correctly without
gaps at the tail. On the main areas of the roof slope, the tail of each
stone slate rests on two thicknesses of stone slate in the course next
but one below. At the eaves, the first full course rests on only
one thickness - the eaves slate. Essentially, the tilt replaces the missing
Torching: lime and hair mortar applied
to the underside of stone slates to render them wind proof. Synonym: tiering;
Torching: half torching: application
of lime and hair mortar between the top edge of the lath or batten and
the underside of the slates. Synonym: single torching;
Torching: full torching: application
of lime and hair mortar between the top and bottom edges of the laths or
battens and the underside of the slates;
Torching: single torching: see half
Unweathered, of stone slates: rock which
is too deep to have been subjected to weathering and consequently has to
be split by mechanical action or frosting after extraction.
Weathering (of rocks): the process by
which rocks are broken down and decomposed by the action of external agencies
such as wind, rain, temperature changes, plants and bacteria. In the development
of weathered stone slates, it is often very thin clay or mica beds which
are weathered out;
Weathering (of stone roofing): the processes
of mineralogical change, particle deposition and plant growth which change
the apppearance of slates on the roof.
Weathering (of a roof): the arrangement
of the parts of a roof covering - the slates, soakers, flashings, mortar
fillets etc - which prevent water getting into the roof.
7 hundreds (840 slates) plus 13 large
each hundred is 40 cases (120 slates)
each case is 3 slates