Damp proof course (D.P.C.) of
cement concrete should have a mix of 1:2:4 or 1:1 ½:3 usual thickness 2.5 cm to
4 cm.
This is usually a layer of
cement concrete mixture in proportion 1:2:4 mixed water proofing compound laid
in between the plinth and superstructure walls to prevent the rise of water by
capillary action from the ground.
Materials
Coarse aggregate shall be of
clean, hard and dense stone chips 12 mm down and shall be washed before use.
Sand shall be clean, sharp and coarse of average 5mm size and shall be free
from dust and dirt and screened before use. Cement shall be fresh Portland
cement. All the materials in use including water proofing compound shall be of
their respective standard specifications.
Mixing
Coarse aggregate and sand shall
be measured by volume with gauge boxes and cement by bag having a weight of 50
kg or volume of 0.0347 cu.m. Some sample tests of cement bags shall be made at
work site to ensure the specified weight and volume. The mixing shall be done
on a clean solid platform. Dry coarse aggregate shall be stacked evenly on the
platform. Sand and cement in the specified quantities at first shall be mixed
dry till of uniform colour and spread over the stacked coarse aggregate. The
materials shall then be turned over once without adding water and then at least
further 3 times, adding the required quantity of water gradually and slowly to
give a uniform concrete. Water-proofing compound about 5 to 3 percent by the
weight of cement as specified shall be mixed with concrete to make it water
proof.
Preparation of base
The top of the walls on which
damp proof course is to be laid shall be constructed with bricks on edge or
with frogs of the bricks down. The top of the plinth bed over which damp proof
course is to be placed shall be thoroughly cleaned with a steel brush, washed
and wetted before laying the course of concrete. Wooden straight edges shall be
fixed on plinth wall having the same inner width as that the required width of
the D.P.C.
Laying
Damp proof course may be laid
to the full width of the plinth or of the superstructure as specified in the
drawing or specially mentioned. It shall be laid to the specified thickness
(2.5 cm or 4 cm) over the plinth wall flush with the floor surface and shall
not be carried across the doorways or such other openings D.P.C. shall then be
consolidated by tamping and levelled
both longitudinally and transversely. Laying shall be completed on same
day; the joints or breaks shall be given at the door opening. The surface of
the concrete shall be roughened and chequered when air dry so as to form a key
for the joint with the brick wall above.
Curing
Damp proof course shall be kept
wetted for at least 7 days after laying, if the brick work is not ready to
proceed further. But in any case no brick work shall be commenced on the
freshly laid damp proof course unless the D.P.C. has been flooded with water
for at least 48 hours.
