Oakley, Votty and Bowydd Slate Quarries Company:

Colloidally coloured slates


Some words are missing from my copy of this document. The gaps are shown as [...] and guesses at the missing words as [italic].

Colloidally Coloured Natural Slates

The Master Builder May 1938

It may not be too widely known that roofing slates can now be had of any colour required. Nor can it be too greatly emphasised that the [colours of the] slates are permanent. White for the tropics which reflects 74 per cent. of the sun's heat; Black reflecting only 10 per cent.; Blue‑green, a most attractive colour; Metallic green having [a hint of] yellow; Plum coloured; a combination of Browns; any colour. And the extra cost of having Colloidal coloured slates is only £5 on a £1,000 house.

Welsh slate producers have for many years been confronted with two problems, on the solution of which depends their whole future. It cannot be too sweeping a statement, to add that without a solution the days of slate quarrying and roofing seem to be numbered on [..] the rapidly increasing costs are having to be passed on to the customer.

The greater problem is the disposal of the waste rock, which accounts for 90 to 97 per cent. of the tonnage handled; while the cost of getting it amounts to about 25 per cent. of the total value of the slate. In other words, the [cost of] roofing slates could be reduced by 33 per cent. If the quarry could find a market at 3/6 [for] the waste rock, the annual [quantity of] which runs into millions of [tons]. It follows therefore, that if the quarries could process this waste, and [sell] it at a profit, the price of world’s best roofing material [could be] further reduced. But the [quarries are] all situated in such remote [places] that rail freights render it [difficult] to find any market except […] one for slate dust. It is the mineralogical structure  of slate which makes it such a durable material, but this merit is, when the rock is pulverised into an inert powder, of [similar] composition of clay but [lacking the] latter's plasticity. It is principally a pure silicate of alumina […] percentages of the three, 25 and 10 respectively. The […] be extracted profitably if power were available at […] of a penny per unit, though […] disregards any residual […] the silicate (for brick making, […]) chemistry could transpose the […] of silicate and alumina, the rock would be it natural […]

[Slate waste] is difficult to handle mechanically, owing to the planes [in which] the rock cleaves. The bigger power shovels can cope with it, but they are too big to operate in mines, even if they could be taken to the working faces through the miles of small level tunnels. These working faces, whether in mines or quarries, are ever getting deeper and farther away from the tipping grounds; and the resulting heavier costs coincide with higher rates of labour, higher taxation, and ever increasing expense on labour welfare and safety measures.

Therefore it is not surprising to those who know the conditions that the price of roofing slates is about three times what it was in 1914. Nor is it surprising that during the last twenty years all intense competition has resulted from the number of new substitutes ; and it is perhaps the best possible tribute to the merit of state that it still survives ; that, by comparison, it is cheap at almost any price. In fact it is probably true to say that these artificial roofing materials (and by " artificial " is meant everything except slate) only gained It footing because of their less drab colour and that price had little to do with it. For, after all, the Englishman has always defended his castle, whether that castle be at home or a bungalow overseas, at the price or his life if necessary, let alone at the price of a few slates. The new factor is Mrs. Englishwoman, and her newly won emancipation has reflected itself in colour schemes everywhere, including the fabric of the house she lives in. Slate was dubbed as drab and for many new house owners it reminded them of the rows of terraces from which they had with difficulty extricated themselves. They did not know what the landlords of those terraces knew: that it was the slate roof that kept the houses intact.

Mrs. Englishwoman's instinct for colour was right and healthy, and it was not her fault that the new roof lost its colour so soon, either because or fading or because it could not clean itself of soot. Neither was it her fault that the roof began to leak almost as quickly, and that repairs only made things worse. No; she had not been told these things. The slate quarry owners had never taken any pains to tell her. She. and thousands of her kind, are now faced with the expense of entire stripping and re‑roofing, at a cost sometimes amounting to £200. If must be slate this time; something that will last at least as long as the house (and then have a high second hand value); and this time the slate quarries are coming to her aid; complete with a colour scheme too, and one that is really attractive and as durable as the slate itself.

It is attractive firstly because it is endless in its variety, and because it does not " paint the lily," but enhances the beautiful natural texture of the cleaved rock. The effects are obtained by the use or the recently patented. colloidal colours: chemical solutions which have an affinity for the slate and which, by mineralogical action, become part and parcel of the slate surface. It is a surface treatment only, but it has withstood all known tests for removal, such as boiling in acids, alkalis and concentrated sea‑water. During the last five years many hundreds of houses in all parts of the country have been roofed with these " Colloidal " slates, while the treatment is applied to slates from any reputable Welsh quarry. The cost is one shilling per square yard of roof; merely an extra £5 on a £1,000 house.

The claim that the colloidal slate is fadeless is not, however, unique ; for there is one and only one other roofing material which has as good a claim: the glazed tile, made only in the interlocking pattern, single lay. But it is more expensive than colloidal slate, and needs also a much more expensive roof under-structure to make it weatherproof. Therefore it can truly be claimed on behalf of colloidal slates that they offer the cheapest form of lasting colour. There are white colloidal slates for the tropics which reflect 74 per cent. of the sun's light. They can be had in black (reflecting only 10 per cent.; while in-between is a vast range to suit all tastes.

One or the attractive newer colours is a peacock blue‑green which is not too exotic if used only over dead white walls when the effect is extremely satisfying if alizarin‑green shutters surround the windows. Then there is it rare metallic‑green, having no trace of yellow in its composition, which also appeals strongly to architects and other artists. Even those difficult plum‑coloured brick walls have been catered for with an intriguing combination of browns. And ill order that the full effect should not be spoiled by unsuitable " trimmings," inexpensive colloidally coloured ridge and hip tiles to match may be ordered with tile slates.

And now it is only fair to point out the "snags". Testimonials have been received from numerous users saying that the states are as bright as ever. One can imagine that such testimonials might well be less enthusiastic in a few years' time when the roof is still brilliant while the rest of the building has toned down in the natural course of weathering. Thus it is particularly necessary to exercise restraint in choosing the colours especially when the choice is made indoors, as the coloured samples will then appear to be much duller than when on the roof. In general, regard should be had for the tones in the surrounding landscape and foliage. 'It is an artistic achievement to obtain an equally satisfying effect at close quarters and at a distance. At three hundred yards the house should melt into its environment. This does not necessarily mean that nothing daring may be attempted; for even white and Reckitt's blue will be com il faut at a southern coastal resort.

Tile second snag is in respect or the roof stain caused by lead flashings. This stain shows up much more on coloured roofs, particularly on greens; so copper is recommended, and is no more expensive than lead since much thinner sheets cart be used. That weighing 16 oz. to the square foot is amply strong and durable, and its thinner flashings make for a neater looking roof.

There are no other known snags, but it should be emphasised that copper nails will hold the slates on the roof indefinitely, and are therefore much cheaper in the long run.

But if the problem or colour has been satisfactorily solved, there still awaits an opening for the man who can find a profitable use for the slate waste.




Colloidal roof in Augustus Road, Wimbledon Common, London