The traditional skills in producing slates are still practiced except today the rock is blasted from the face brought down to the production sheds where it is then split into smaller lumps of rock and eventually split down the cleavage by hand into various slate sizes and edge dressed. Standard nominal sizes vary between 250 x 150mm up to 600 x 350mm .
Up until the end of the Second World War slates were probably the most commonly used roofing product with slate forming part of the industrial base along with coal of the Welsh economy there being numerous small slate quarries in North Wales, the largest and most famous being the Penrhyn Slate Quarry near Bangor, in those days owned by Lord Penryhn and which is which is still quarrying today; subsequently sold to the McAlpine Group who later sold out and is now trading as Welsh // Slate. Dependant on the Rock seam the slates can vary in colour from the traditional blue to varying shades of grey and occasionally to green and red.
One of the most famous slate quarries was the Oakley Slate Quarries Co in Blaenau Ffestiniog which having closed some years ago but is still producing slates, is now a museum open to the public and a tourist attraction under the name of Gloddfa Ganal. Oakley slates are blue-grey in appearance. Another quarry, still in production is that of J W. Greaves & Sons Ltd whose Llechwedd Quarries are also located at Blaenau Festiniog in North Wales. Portmadoc used to be the seaport outlet for these quarries. Many of the smaller quarries have been taken over and incorporated into one leading player in the industry.
Another famous quarry was situated at LLanberis and it was called Dinorwic Slate Quarries Ltd. This quarry is now the site of one of the biggest pump-storage electricity generating site in Wales
Across the Midlands, Lancashire, Yorkshire and into Scotland slates were and still are quarried and in many instances slate quarried over 100 years ago are still being reused such is and was the quality of the UK slate familiar names are :-
Burlington Slates from Ulverston are still being quarried and are produced as both standard sizes and in random widths and lengths, commonly known as Random Slating, being laid in varying lengths in graduated diminishing courses up the roof slope. This style of slating requires a lot of skill by the Slater in sorting, grading then laying slates being delivered to site by tonnage rather than by count. Also from Cumbria are the well-known Westmorland Green Slates which are still quarried
Swithland slate (a Leicestershire slate no longer quarried) but still in demand from reclamation, being laid as Random Slating courses, mainly restricted to Leicestershire.
In Cornwall slates are still quarried at the Delabole Quarries near Camelford.
Scottish slates are again mainly obtained from reclamation and tend to be smaller in size and random sizes. Although there are quarries in various parts of Scotland, the most popular come from the Firth of Lom on the west coast and are commonly called Ballachulish Slates.
(Sandstone and Limestone)
Collyweston limestone slates, again no longer quarried, the rock forming the slates was dug out of the quarry during summer months and left over winter when the frost would split the rock forming the slate, again laid in random courses.
The roofs in old Stamford are virtually all Collyweston slate, an interesting fact is that Collyweston slate was used to roof the Mansion House in London when first built and later when extended, the slaters coming from Collyweston to carry out the work. These slates are also prominent in the Cotswolds and Purbeck.
Gritstone slates from the Pennines sometime called Yorkshire Grey Slates are large thick and heavy, also being random slates in diminishing course.
Sandstone slates (random slates) are to be found in south east Wales and Herefordshire, also in Cumbria and parts of Scotland
The above is just a brief resume of the slate industry.
Whilst probably not as old as slate, clay roof tiles have formed an important part of the roofing industry, they are a man made product from clay or concrete being manufactured in many shapes and sizes dating back to Roman Times
The straw laid over the mud huts was layered with wet clay which dried out forming a coating over the straw / reeds
The original roof tiles would have been made from clay being hand moulded, pressed and then brunt in a kiln. We know from the formation of our Guild that they were in use as early as 1200, with regulated wages for tiler’s from 1212; it would be a fair assumption to say roof tiles were being made before the Roman Times.
History would show that wherever clay was found it would have been used to make tiles, not always successfully, as the composition of the clay would cause them to gradually break up after severe winters resulting from rain and frost action. As such not all clay is suitable for tile making Berkshire, Cambridgeshire, Gloucestershire, Leicestershire and areas around the Humber being well known for the quality of the clays found in those areas producing high quality hand made clay tiles, Cambridgeshire being particularly noted for it’s nibless tiles fixed with wooden pegs; whilst Staffordshire clay grounds are noted for their machine made tiles being made from the harder clays found in that area.
The process of making tiles varied depending on whether hand or machine made. Tiles were being produced in both cases where the clay is used in the plastic state, traditionally in the case of the handmade tiles soft plastic “pugged” clay is used the tiles being moulded individually and shaped by hand, sand being spread over the mould to assist more easily for the tile to leave the mould and assist the sand faced finish, After a drying period the tiles are stacked on pallets and they are then ready for the kiln.
In the case of machine made tiles the prepared clay is rolled out like a ribbon and automatically cut off into the required length called “Bats” these are then stored in the “Bat House” to allow the moisture to evaporate after which the tiles are placed in a kiln for firing, which today is controlled by computers and not as formerly by a skilled “Firemen” stoking the Kiln, Consequently the science is more exact producing a better quality product
The advent of concrete tiles after the war being very much cheaper gradually forced the closure of a number of clay tile makers, pleasingly they are still available, and to the eye of the beholder having a more pleasing effect on the eye being softer in appearance.
Concrete roof tiles are manufactured from Portland cement, aggregate, pigment and water under a high pressure compaction and extrusion process the whole process being automated. The concrete is mixed in a rotating drum then transported to the production line on a conveyer.
The tiles are formed in moulds – known as ‘pallets’ these run continuously along a production line. The top surface of the tile is formed using rollers and scrapers.
The concrete mix is dropped into a box (known as a roller box) containing the rollers and scrapers which is situated over the production line. The pallets pass under the roller box so the concrete forms into the shape of the pallet and the rollers. After the roller box a knife cuts the concrete between each pallet to form the individual tile, if nail holes are required punches are added to the knife to form the holes at the same time.
The pallets continue along the production line into a drying chambers for the wet tiles to set, once set the pallets go back onto the production line where preset horizontal knives separate the dry tiles from the pallets. The tiles are then placed on pallets, shrink wrapped, stored awaiting delivery.
Both clay and concrete roof tiles come in various shapes and sizes, small to very large, the smaller tiles being laid double lap and the larger format to a single lap. Tiles are also produced in ornamental shapes mainly used for vertical cladding to fronts and upper stories of buildings.
Alternative Materials for roofing include Canadian Cedar Wood Shingles, Fibre cement slates and more recently the introduction of both Plastic and Polymer traditional sized slates and tiles.