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PILING.
69
Ordinary immersion will suffice, but the imprégnation is
pressure.
None of the last three methods has proved so
effective, or corne into such general use, as creosoting.
In fact, it is doubtful whether any of them is of the
least benefit in warding off insectile attack, and this, in
maritime situations, is an object no less important than
the preservation of timber from decay.
The only apparently completely successful way in
which timber may be guarded in this respect is by
means of some external covering excluding the wood
from actual exposure.
Sheathing" is a protective device which consists in
enveloping a pile in a covering of metal, earthenware, or
other material impenetrable by insects. A thin covering
of copper plates has proved satisfactory in repelling
worms from piles, when the covering has extended from
below the mud level to above high water-mark ; other-
wise the insects intrude themselves between the metal
and the wood. The method is obviously an expensive
one, and therefore not likely to commend itself for
general adoption. Zinc has been tried as a substitute
for copper, but it is soon corroded by sea water. Muntz
metal is another substitute, but its application has
been too limited for definite judgment of its powers.
Studding with broad-headed scupper nails is an old
expedient, the principal drawback of which is its
troublesomeness, and, of course, its expense.
Earthenware pipes, such as ordinary drain-pipes, and
cylindrical casings of wire netting bedded in concrète,
are efficient preservatives of piles in situations free from
shocks, collisions, and erosion. The space between the
pipe and the pile must be filled in with sand or cement
grout. A simple coating of Portland cement has been
tried, but the film is too thin and easily cracked. Lately,
a system of facing wooden piles with reinforced concrète
slabs has been promoted by Mr Cooper Poole, the harbour
engineer of Southampton. The slabs are primarily in-
tended for application to piles which are in such a
state of dilapidation as to call for renewal or repair.
At each corner of the pile a small angle iron is spiked
on to the timber so as to form a guide for the slabs.
These last are connected up and allowed to sink into
the mud until they take a bearing, when the inclosed
space is filled with concrete. The system, however, is
expedited by using
Fig. 61. —Application
of Reinforced Con-
crete Slabs to De-
cayed Timber Pile.