Practical Use Of Stone Surface Materials Roof Covering

Before the work starts, slate tiles are sorted into two, three or four groups of different thicknesses, unless this has already been done at the quarry. The underlay is usually a timber board roof with bitumenfelt.The slates are fixed onto battens, most commonly 25 x 50 mm.The distance between the battens depends upon the type of slate and its dimensions, and is usually decided by the distance between the lower edge of the slate to the fitted nail holes or notches, minus the overlap.

The thickest slate is laid furthest down on the roof, to avoid large variations in thickness on the other courses. A special slate hammer is used to split and shape the tiles, if necessary.The tiles are fixed with special slate nails that are 25/35 mm, 28/45 mm and 28/55 mm according to the thickness of the slates. These are a critical part of the construction and should be of especially high quality.The nails are never hammered in completely; a little slack is left so that the slates can move. If they are nailed tightly they will crack. The ridge is then covered with rectangular slate tiles, timber boarding, zinc, copperor even turf.

Rough tiles. When laying rough tiles, holes are first bored or hacked into the tile with a drill or a special hammer. The tile is fixed to the batten with a strong galvanized nail. For large tiles wooden pegs made of ash or juniper can be used. As rough tiles do not always lie tightly on each other, they can be broken by heavy snow loads. One way of resolving this problem is to put lumps of clay under the end of each tile. If time is spent sorting the tiles so that they fit well together, then a roof of rough tiles can be as waterproof as any other.

Patchwork tiles (Figure 15.2). Patchwork tiles can be laid as a single or double covering. A double covering with a minimum slope of 18° can tackle most climates. With a single layer the slope should be a minimum of 22° in moderate climates and more than 27° in severe climates.

For single laying the tiles must be at least 12 mm thick. For double laying they need only be 6 mm thick.The distance between the battens for double laying is somewhat less than half the length of the tile. An overlap of at least 50 mm is recommended.

Patchwork tiles can also be used on rounded corners, and with some modification on conical, spherical and cylindrical forms.The main rule is that the size of the tile is reduced proportionally with the radius it is to cover.The tiles are nailed directly onto the rough boarding of the roof. To avoid the stone splitting because of the movement of the roof, each tile must be fixed to only one piece of boarding.

Square tiles (Figure15.2).The square tile is used for single-layer roofing.The overlap should be at least 45 mm for small tiles and 75 mm for large tiles.

WALL CLADDING

It is seldom advisable to fx thin stone tiles directly to a wall with mortar. The tiles can easily loosen or be broken. This can happen either through expansion when exposed to the sun, or by the formation of condensation behind the tile that then freezes and pushes it off. If the grain of the tile is vertical, there is a stronger chance of it being knocked of by frost than if the grain is horizontal. Cut stone cladding is therefore usually mounted on special metal anchoring systems, with good ventilation behind the stone. The metal ties should be stainless steel or a copper alloy, and are bored into the structure. This type of cladding is expensive and is most often used on offices or public buildings.

Slates for cladding can be used in the same way as for roofing. Most forms can be used, though patchwork and square tiles are the most appropriate because of their lightness. Only one layer is needed, and is mounted with slate nails, with good ventilation underneath.

FLOOR COVERING

A natural stone floor can be laid in several ways. It is common to lay both cut stone and slate inmortardirectlyonaconcrete base.The concrete isprimed witha mixofcement and sand (1:1) while the mortar for laying the tiles is a mixture of cement and sand from 1:3 to 1:4.The mortar is laid to the necessary thickness and before laying the stone tiles are given a coating on the underside with a cement and sand grout (1:1). The tiles are then knocked carefully into place with a rubber hammer. The joints are filled between three and seven days later with a grout of cement and sand (1:3).

For larger floor tiles hard deciduous wood can be used in the joints instead of mortar, or the mortar can be replaced with sand.The possibilities of re-use are then very good.

Marble isthe only stonethat needs regular maintenance.This is carried out with wax or polish.

(a) Single lap pantile (b) Double lap pantile (c) Interlocking pantile

(d) Interlocking double panlile

(e) Inlerlocking single (f) Rat Interlocking panlile pantile

(d) Interlocking double panlile

(e) Inlerlocking single (f) Rat Interlocking panlile pantile

15.3

Roof tiles in fired clay (a-c) and concrete (d-f). Non-interlocking tiles require a steeper roof.

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