VITRIFIED BRICK AS MATERIAL FOR COUNTRY ROADS. 13 
The sand should be clean and well graded in size, and the stone or 
gravel should conform to the requirements given above in connection 
with the discussion of foundations constructed of those materials. 
Foundations for brick pavements have also been constructed of 
timber boards laid on sand, and in some instances of sand alone. 
These foundations have seldom proved satisfactory for any great 
length of time, however, and can, therefore, be economically used only 
when the pavement is to be constructed of an inferior grade of brick. 
SAND CUSHION. 
Since it is practically impossible to construct an absolutely smooth 
foundation, and since there is always a slight variation in the size of 
paving brick, owing to slight differences in the amount of shrinkage 
at the time of burning, it is necessary to provide an adjustable cushion 
of some kind between the foundation and the brick for correcting these 
slight irregularities, in order to secure an even surface and a uniform 
bearing for the brick. Sand has been found a most satisfactory 
material of which to construct this cushion, and is almost exclusively 
used for this purpose. The proper thickness for the sand cushion will 
of course depend on the extent of the inequalities above mentioned. 
Two inches is the most usual thickness, however, and this thickness 
has generally proved very satisfactory. 
The sand used in the cushion should be clean, free from pebbles, 
and preferably fine grained. If dirt or vegetable matter is present, 
it will soon be leached out and cause unevenness to develop in the 
pavement, while pebbles prevent the brick from securing a uniform 
bearing, and ultimately produce the same result. Fine sand adjusts 
itself to the shape of the brick more readily than coarse sand, and is, 
therefore, given preference. It is also important that the sand should 
be dry when spread, because a comparatively small amount of mois- 
ture increases the volume of fine sand considerably, and moisture 
when present is not, as a rule, uniformly distributed. Even if it were 
uniformly distributed at the start, some spots would dry out more 
rapidly than others while the spreading was under way, and a lack 
of uniformity would thus be produced in the cushion. 
In forming the cushion the sand is uniformly spread over the 
foundation to a depth slightly in excess of that desired, and is then 
smoothed off by drawing over it a template shaped to conform with 
the cross section of the finished pavement. The length of the tem- 
plate is ordinarily made equal to the width of the pavement where 
this is less than about 25 feet, and equal to half the width for wider 
pavements. Timber guides may be laid in the same direction as the 
pavement for the template to slide on, or the curbs may be made to 
serve as guides where this is convenient. 
After the cushion is spread and uniformly "struck off" with the 
template to a depth slightly in excess of that required, it should be 
