BUILDING FOUNTAINS AND PONDS - Fountain
and Garden Ponds 8
Pools are seldom based deeply enough
to carry their bottoms below the frost
line except in regions with very mild
winters where an excavation deep enough
for the pool itself is also below the
depth to which the ground freezes. Good
drainage of the soil under a concrete-lined
pool is therefore important in cold climates
in order to avoid excessive frost damage.
In clay soils the excavation
for such a pool should be made 4 to 6
in. deeper than is necessary for
the masonry, and this additional space
is used for a layer of cinders
or coarse gravel. In some locations,
especially where the pool is both on
water-retentive soil and on a low spot,
tile under-drainage
is advisable. Under-drainage of metal-lined
pools is less important.
because linings of this kind are not
easily damaged by frost. In rare
instances a considerable accumulation
of water may bulge a metal
lining enough to pull it away from the
drain pipe, but this would
occur only on unusually wet sites and
it can easily be forestalled by
a layer of compacted gravel under the
bottom.
Under-drainage is not required for clay-lined
pools. Clay-lined
pools are usually left filled during
the winter and seldom suffer
damage from frost. If damage does occur,
repairs are so simple that
precautions are unwarranted. If the pool
is to have supply and drain pipes, they
should be installed before the lining
is built. The trenches which
bring them to the pool should be dug
and the pipes should be installed all
the way to the pool and the joints tested
for leaks. The
supply piping is easily tested by capping
the end of the pipe, then
turning on the water. If no leaks show
up at the joints in two or
three hours, the line is watertight.
The drain pipe can be tested by
capping or plugging the lower end, then
filling the pipe with water.
After the pipes have been proved to be
free of leaks, the trenches
can be filled in and the fill will hold
the pipes rigidly in place. In
order to keep trash out of the pipes,
their ends should be kept closed
until the work on the pool is done. Care
must be taken to have any
fittings which are to be embedded in
the masonry, such as the coupling in
the right position.
Concrete-lined pools
A 1:234:4 concrete
mix
is satisfactory for the lining of garden
pools. For linings 4 in. in
thickness, the gravel used should have
no pieces larger than \Yi in. in
diameter. Linings are usually placed
without forms. Concrete of a fairly firm
consistency is simply shoveled or troweled
into the excavation and is smoothed out
with steel or wood floats. The placing
begins at the center, and the work-
man gradually backs out of the excavation
and produces the lining
at the sides while leaning over the
edge. While working on the edges,
he should kneel on planks so as to
avoid causing crumbling of the
soil. Sides not over 12 to 15 in. high
can be readily shaped with a
trowel and a float if the concrete
is not too wet. Any slump that
develops in the first few minutes can
be corrected by pulling upward
along the face of the concrete with
a trowel or float. If the tendency
to slump persists, the concrete contains
too much water. Mixing
another batch will, in most cases,
be much less costly than construcitng
forms.
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