Roof Slating & Tiling

Possibly one of the oldest if not the oldest craft in the Building Industry.  From the time man came out from sheltering in caves to avoid the elements, to building Mud Huts using reed and straw matting to form a covering from the extremes of nature, roofing has evolved to present day manmade products alongside the traditional natural slate and stone and reeds, which are still used today for thatching but to a very much lesser degree.  Let us look at some products and the various terminology in their application:

Natural Slates

(Metamorphosed Shale)

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, Slate formed part of the industrial base, along with coal, of the Welsh economy and there were numerous small slate quarries in North Wales. The largest and most famous of these was the Penrhyn Slate Quarry near Bangor, which was then owned by Lord Penryhn, who subsequently sold it to the McAlpine Group. It was later sold to Welsh Slate, under which name it now trades and is still quarrying today; 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.  This closed some years ago, but is still producing slates, and now also houses 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 is a Leicestershire slate that although no longer quarried is still in demand from reclamation, being laid as Random Slating courses.  Its use is 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.

Other Slates

(Sandstone and Limestone)

Collyweston limestone slates are also 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, and also in Cumbria and parts of Scotland

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The above is just a brief resume of the slate industry.

Roof Tiles

Whilst probably not as old as slate, clay roof tiles have formed an important part of the roofing industry.  They are a manmade 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 fired in a kiln. We know from the formation of our Guild that they were in use as early as 1200, with regulated wages for tilers 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.  This was 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 are well known for the quality of the clays found in those areas, which produce high quality, hand made clay tiles.  Cambridgeshire is particularly noted for it’s nibless tiles fixed with wooden pegs, whilst Staffordshire clay grounds are noted for their machine made tiles, which are made from the harder clays found in that area.

The process of making tiles varied depending on whether they were hand or machine made, and tiles were being produced in both cases where the clay is used in the plastic state.  Traditionally, handmade tiles use soft plastic “pugged” clay with the tiles being moulded individually and shaped by hand.  Sand is spread over the mould to assist the tile to leave the mould and producethe sand faced finish.  After a drying period the tiles are stacked on pallets and are then ready to be fired in the kiln.

In the case of machine made tiles, the prepared clay is rolled out like a ribbon, which is cut 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. 

Today's kilns are controlled by computers and no longer by skilled “Firemen” who stoked the Kilns. Consequently the science is more exact and produces a better quality, more consistent product.

Concrete roof tiles started appearig after the Second World War and being significantly cheaper, they gradually forced the closure of a number of clay tile makers. Clay tiles are though still available and have a much softer 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’, which run continuously along the production line, and the top surface 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 that the concrete forms into the shape of the pallet and the rollers. Afterwards a knife cuts the concrete between each pallet to form the individual tiles.  If nail holes are required then punches are added to the knife to form the holes at the same time. The pallets continue along the production line into a drying chamber for the wet tiles to set.  Once set the pallets go back onto the production line where preset horizontal knives separate the dried tiles from the pallets. The tiles are then placed on pallets, shrink wrapped, and stored awaiting delivery.

Both clay and concrete roof tiles come in various shapes and sizes, small to very large, with 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.

Note:

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.