Elliott Roofing

History

The Collyweston Slate Roof

Collyweston Slate is unique to this area and has been used for many hundreds of years, certainly since the Roman occupation. The source of true Collyweston is restricted to a particular strata of limestone lying about 25 feet below the surface in an area stretching, roughly, from Easton-on-the-Hill to Duddington with the village of Collyweston more or less at the centre. The use of this marvellous slate, apart from a few exceptional buildings further afield (London's Guild Hall, Nuffield College Oxford and even a mansion on Long Island, New York), is restricted to an area of about 20 miles radius from it's source. More important buildings such as Manor Houses, Town Halls and Coaching Inns may have Collyweston roofs still further afield than that. The slate is mined or quarried (open cast) being brought to the surface in large blocks known as "logs". These need to be subjected to several nights of hard frost, with subsequent thawing, which splits the "logs" into slate, which is not only flat, but of very uniform thickness. The freezing must take place before the "logs" dry out, or lose their "quarry sap". Once dried-out a "log" cannot be re-moistened, so, once exposed to the atmosphere above ground, they need to be kept watered to prevent drying out. A large "log" can yield slates up to 30" in length. It can be seen that the production process is very dependent on winters with a period of hard frosts. During the latter half of the 20th. century, though there have been experiments with artificial freezing, roofing and re-roofing has had to rely mainly on slate obtained from demolished buildings, or, when re-roofing, from salvaged slate. Up to 75% can be recovered and, as replacement slate is so scarce and expensive, great care is taken to save as much as possible.

The Mining Process

Having sunk the access shaft to the required level, the next stage is the extraction of the layer of sand, varying in depth from 3 to 5 feet, from below the Collyweston layer. Traditionally this was done by a worker lying on his side and pecking away at the under-lying sand and soft sandstone with a small pick, known as a "Foxing Tool". Though not certain, it seems probable that the sand, so extracted, would have been used in making the mortar for fixing the slates. As the sand was removed, the over-lying strata of the Collyweston seam was supported by columns built of "bastard" (i.e. unworkable) rock. When required, the columns would be removed and the Collyweston strata would either fall or be levered from the roof of the workings. The "logs" would then be moved along passages to the access shaft and hoisted up to ground level. The whole mining process was laborious, arduous and potentially very dangerous. It is probably this factor, highlighted by increasingly stringent industrial safety regulations, as much as the lack of hard frosts, that has limited the production of new slate in recent years. Under today's conditions, open cast quarrying would seem to be the only practicable means of obtaining supplies of Collyweston "logs". It is probably sacrilege to mention it in these notes, but a concrete simulation of Collyweston is manufactured by several companies and this, used on unimportant buildings, in not too conspicuous positions, can provide an opportunity to economize in the use of the real thing. These simulations do weather quite realistically.

The Mining Tools

Picks, shovels, crow-bars, ladders, sheer-legs, pulley blocks, ropes and baskets would all be required in the excavation of the access shaft. For the actual extraction of the stone, the foxing tool, described previously, and heavy quarry bars, for levering, would also be required.

Slate Dressing

Once frosted, the "logs" would need some encouragement to  part into their separate layers of slate. To do this a "cleaving hammer" was used. The slates being "dressed" into the appropriate lengths and random widths using a "dressing hammer". Finally, the hole in the top edge would be made using the "bill and elves", a sharply pointed narrow pick with a short handle. Though now-a-days an electric drill can be used, you can't mechanize the dressing of the slates. Once dressed and drilled, the slates are stood on edge, in rows, according to their lengths. Measurement of slate sizes is made with the "Slater's Rule". This is a piece of lath, about 3 feet in length, on which the various slate sizes are marked with a shallow saw cut and the name of the slate (see Glossary) is written in abbreviated form.