After the concrete has been poured, care should be taken that it does not
dry out too quickly, and in hot weather it must be protected from the
sun. Exposed surfaces and objects made of dry concrete should be sprayed
thoroughly with water twice or oftener each day for a week or 10 days.
Sometimes surfaces are shielded with canvas, paper, boards, or layers of
moist sand.
[Illustration: Fig. 16.--Tremie for use in placing concrete under water.]