apt to be very porous, which in
certain positions is a very grave objection to it--this, not only from
the fact of its porosity, but from the liability to disintegration
from water freezing in the crevices.

Concrete, when ready to be placed in position, should be of the
consistency of a pulpy mass which will settle into place by its own
weight, every crevice being naturally filled. Pounding dry concrete is
apt to break adjacent work, which will never again set properly. There
should be no other object in pounding concrete than to assist it to
settle into the place it is intended to fill. This is one of the evils
concomitant with imperfection of mixing. The greater perfection of
mixing attained, the nearer we get to the ideal monolith. The less
handling concrete has after being mixed, the better. Immediately after
the mass is mixed setting commences; therefore the sooner it is in
position, the more perfect will be the hardened mass; and, on the
other hand, the more it is handled, the more is the process
interrupted and in like degree is the finished mass deteriorated. A
low drop will be found the best method of placing a batch in position.
Too much of a drop scatters the material and undoes the work of
thorough mixing. Let the mass drop and then let it alone. If of proper
temper, it will find its own place with very little trimming. Care
should be taken to wet adjacent porous material, or the wooden form
into which concrete is being placed; otherwise the water may be
extracted from the concrete, to its detriment.

It has been found on removing boxing that the portion adjacent to the
wood was frequently friable and of poor quality, owing to the fact
just stated. It is usual to face or plaster concrete work after
removing the boxing. On breakwater work, where the writer was engaged,
the wall was faced with cement and flint grit, and this was found to
form a particularly hard and lasting protection to the face of the
work.

Batches of concrete should be placed in position as if they were
stones in block masonry, as the union of one day's work with a
previous is not by any means so perfect as where one batch is placed
in contact with another which has not yet set. A slope cannot be added
to with the same degree of perfection that one horizontal layer can be
placed on another; consequently, where work must necessarily be
interrupted, it should be stepped, and not sloped off.

Experience in concrete work has shown that