STONEWORK 37 



Pieces of slate slab, or of dense non-porous stone, are also used as 

 ties, but are apt to break should the two portions of the wall settle 

 unequally. 



Ties, spaced about two feet apart horizontally, may be inserted every 

 third course of brick-work. The ties forming any one horizontal row 

 should be situated over the middles of the spaces between the ties 

 of the horizontal row next below. 



Sometimes the thinner portion of a hollow wall is built on the outside, 

 sometimes the thicker. The former method is probably the better, since 

 only the thinner portion can become wet, and also because the two wall- 

 plates (which are built into the thicker portion of the wall) are closer 

 together, resulting in a smaller effective roof span and therefore a lighter 

 roof. 



It is a good plan to commence the cavity below the level of the damp 

 course. The latter will then be above any water which may accumulate 

 at the bottom of the cavity (see Fig. 31). Very hard bricks, built in 

 cement mortar, should be used below the damp course, and these bricks 

 should be rendered or plastered with cement mortar on their surfaces 

 next the cavity. 



When the 4^-inch portion of a hollow wall is on the outer, or weather 

 side it should be rendered with good plaster to a thickness of about 

 | inch, and the plaster should be painted with a good water paint. 



The dairy illustrated on pages 174-5 is provided with hollow walls. 



Stonework. — Building in stone calls for more skill than does building 

 in brick, because the mason receives the stones in irregular shapes and 

 sizes. Due attention should be paid to the provision of proper bond, 

 which is much more difficult to arrange for than when bricks are used, 

 and which therefore cannot be expected to be so perfect as in brickwork. 



In the case of stratified rocks, such as sandstone or limestone, the 

 stones should be laid on their natural led, i.e. with the layers, or lamina, 

 of which the stone is built up, in a horizontal position. Stones without 

 a definite stratified structure such as dolerite (also called iron-stone or 

 ijzer klip) may of course be laid in any convenient position. 



Stone walls are built in a manner similar to that already described 

 for brick walls, the coiners or quoins being raised first to a height of 

 about 3 feet, the plumb-rule being used to keep them truly vertical. 

 The space between the quoins is then built up, a line stretched from quoin 

 to quoin serving as a guide. 



