452 The Architectural Review and American Builders' Journal. [Jan., SLATING AND SLATE. THERE are various different methods of securing slates on the roofs, which we will briefly discuss. Some- times they are fastened on lath, usually termed shingling laths, which are nailed on to the rafters, the latter being spaced apart, just so much as the slate is ex- posed to the weather. In this case, it is requisite, that a full coating of plasterer's mortar should be given be- neath the slates and between the laths, and not simply pointing lightly along the joints and edges. The main object of this full coating is to prevent the passage of currents of air or wind, which carry along with them drifting snow, through the crevices which are left, when such is omitted. The practice of simply pointing is one that cannot be too strongty condemned and reprobated, as being nothing. more nor less than an attempt to evade the faithful fulfilment of- a contract, ac- cording to the full intent and meaning of the specifications, in which it is only usual to mention, in general terms, that, when slate are laid on laths, they shall be pointed with mortar, beneath the slate, and between the laths. The object desired is to obtain a perfect air-and- water-tight covering for the roof, which can only be secured by a full coating as above ; and not bjr anj- makeshift, such as simple pointing, which is only resorted to by the slater, for the pur- pose of carrying out, what would seem to be the letter, but not the spirit, of the contract. The result is, that the owner of the building, not being prac- tically versed in such matters, takes it for granted, that the slater has acted up to the contract; and performed all that was required of him, in order to render the roof proof against leakage ; and only discovers the deception and the make- shift, that have been imposed upon him, by finding, during the first winter- storm that he encounters, the snow, drifting in through the crevices, that have been allowed to exist by the simple pointing of the latter, and filling up his loft by the bushel. This practice is the more strongly to be censured, in so much, as it tends to create a very erroneous, but it must be allowed, a natural prejudice against slate roofs in general. We, ourselves, in our own practice, have, on several occasions, met with instances, in which the roofs were condemned, and, for no other reason, than that the slater had been guilt}^ of the very practice, against which we have thought it here a dutj^ to enter our protest. To insure against any such complaints and condemnation of roofs, it is essential, we repeat, that the slate be laid with the proper over-lap, not less than 3 inches ; that the pitch of a roof for slate should never be less than 25 degrees ; and that a full coat of hair mortar be spread, over the whole, surface between the laths. This will effectually close every crevice arid aper- ture against the possibility of admitting any currents of wind, drifts of snow, &c. The mode of securing slate on roofs, which is at present in general adoption, is first to sheath the whole surface with boards, and overlay these with two thicknesses of roofing felt, so-called, but which is nothing more, than thick sheathing paper, saturated with the fluid refuse of coal gas tar, and manu- factured, of late years, principally for composition roofs, such as gravel, &c. On account of the very difficulties, which we have just described, proceed- ing from the practice of some slaters substituting simple pointing for the full coating of mortar, this felt has come into pretty general use, in lieu of the mortar ; and has proved to be a most valuable means of obtaining a sure and secure protection against the weather.
