This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol5", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
This also applies to floors and staircases, and, in fact, to all concrete which is worked into moulds or packed round any supporting material. Concrete floors must in all cases be protected against rain, direct sunshine, and frost, and of course against traffic over them, until they are set, by means of sacking or boarding. Usually seven days' protection is sufficient; but judgment must be exercised, and the covering kept on till the surface is really hard. In the same way, no centering for concrete floors or boarding for concrete walls should be removed till quite a week has elapsed.
Frost is the greatest enemy of all work into which water enters. Consequently brickwork and masonry which is laid in mortar must be built in quick-setting cement, if it is done in frosty weather, or else must be thoroughly covered over at night-time during the winter months, and whenever the temperature falls below freezing-point. Pointing is particularly liable to be attacked, as it lies on the surface of the work, and should never be done, except in cement, at a time of the year when it is likely to be destroyed in this way. Even cement, however, whether in concrete or mortar, must not be allowed to freeze before it is set, else the setting action will be entirely stopped, and the work will break up as soon as the thaw comes, as readily as if nothing stronger than sand had been used.
In masons' work, once the Clerk of Works is assured that the stone is sound, he generally has little trouble; but he ought not to permit hollow bedding unless the Architect particularly asks for it, as, although it results in the production of a fine joint, it renders the stone liable to spall off. He must, of course, see that all joints are properly flushed up with mortar of the character specified, and that backing is properly filled in. Walls which consist of ashlar facing and rubble backing ought to be built very slowly on account of the unequal settlement, and should be provided with good bond stones as frequently as circumstances will permit; and the same remark equally applies to ashlar walls which have a brick backing. It is always best in such cases for the backing to be laid in an eminently hydraulic lime, if not in cement.
The bedding of the stone has been referred to previously. Horizontal bedding is especially necessary in landings and stairs, and is generally insisted upon throughout all mason's work, except in overhanging mouldings, which ought to be edge-bedded, and tracery, which ought to be bedded at right angles to the pressure exerted on the stone.
In all walling, whether it be built in brick, stone, or concrete, the verticality of the face must be preserved and watched, testing it with a plumb-line constantly. In the same way the perpends, or vertical joints, which ought to come above one another, should be tested; while the horizontal courses are tested by means of the ordinary level, or in long lines, perhaps by the use of the Surveyor's level, though this is rarely done. A careful Clerk of Works will always see that stone steps immediately after being laid are covered with boarding to protect them from injury until the completion of the work, and in the same way all projecting moulding and carving has to be covered after execution. A good deal of carving is generally left until the very last, and is worked in situ, so as not to need further protection after the scaffolding in front of it is removed.
Brickwork is similar to stonework in the matters mentioned above, but requires a good deal more attention to secure proper bonding. All bricklayers know how to form simple angles and junctions; but anything that is in the slightest degree out of the common should be specially set out by the Foreman, and submitted to the Clerk of Works for approval before it is executed, his duty being to see that there are as few vertical straight joints throughout the work as possible. This is particularly necessary in flues and chimneys, and in brick piers which are introduced for supporting heavy girders. Footings also need watching. Headers should be used in these to the greatest possible extent, unless each course be a double course, when the lower may consist of stretchers and the upper one be of headers. The proper cutting of arches, whether of brick or stone, needs careful watching; as also does the laying out of the flues, which ought to be parged as they are built, and carefully smoothed out with a trowel, it being now a very rare thing to core them in the old fashion - that is, to build them round a core, or open box of wood with rounded angles, which is drawn up through the parging almost course by course as the work proceeds. Coring is always specified; but it now means little more than passing the sweep's broom through the finished chimney. The most likely things for the bricklayer to slip are the little finishings, such as cement fillets and cement pointing, whether to window frames or to lead flashings, and proper cement weatherings on the top of all over-sailing courses, and as flaunchings to chimney-pots. A good deal of trouble may be caused also by the surfaces of internal walls being improperly finished; being, for instance, left rough when it is intended that they should be whitewashed, or finished off with a neat joint when they are to be plastered. If it is specified that the external facings are to be struck as the work proceeds it is necessary to see that this is done, and that the walls are protected from injury subsequently. It is always much easier to the Builder to leave the joints rough for subsequent pointing and smoothing down, rather than to keep it clean from the outset. It is essential to watch that no stale mortar be used. There is almost always some over at the end of a day's work, and this the men are tempted for their own sakes to work it up next morning, while it is an economy for the Builder to permit them to do so. It requires a Clerk of Works to be at his post as soon as the men arrive if this is to be prevented, should he suspect it being done. Mortar which has once set, whether it be made of lime or of cement, has very little adhesive power afterwards, and cannot be trusted. Cement particularly has to be mixed in quite small amounts, and used quite fresh, as much of that which is now on the market will commence to set within half an hour of the mixing. To a less extent this is the case with the more hydraulic limes, and consequently if they are being used the watermill should be employed with care, else it may continue its work after setting has commenced, and thus greatly destroy the strength of the mortar.