To prevent upheaval by frost a foundation formed of crushed stone, hard
furnace cinders, brick bats broken to about a 2-inch size, broken tile
or any other hard porous material, should be laid in such a way as to
obtain perfect drainage. Never use ashes.
If freezing occurs, room is in this way provided between the pieces of
stone for the expansion of the ice.
[Illustration]
If this foundation is placed in clay soil, side outlets or blind drains
of tile should be provided at points along the walk where they are
necessary, leading into holes filled with cinders or crushed stone,
which will allow the surrounding earth to soak up the accumulated
water. Clay soil holds the water collected in the drainage foundation,
and if it becomes entirely full of water, the ice formed during
freezing weather will upheave the walk.