Waterproofing of concrete structures is done by either suitable extraneous treatments like applying paints, fixing bitumen felts etc. or internally by suitable design of the concrete mix, addition of suitable admixtures in the concrete or mortar at the time of mixing and/or installing water bars at the joints.
The design, material and workmanship should conform to the relevant standard codes where applicable.
a) In concrete: The method of application of admixture and other details is based on the manufacturer's specification.
b) Plaster: The concrete surface, to be plastered, is cleaned thoroughly and kept wetted for 24 hrs. The plaster in cement sand mortar mixed in proportion varying from 1:1 to 1:4 by volume along with the waterproofing admixture and laid in appropriate thickness and in layers not exceeding 15 mm layer or as per manufacturer's specification. The additive. On completion, the plastered surface shall be cured continuously for a minimum period of 14 days like concrete.
Waterproofing of Concrete by Bituminous or Tar Coating
The surface is first sand papered, cleaned and completely coated with hot coal tar pitch of quality as per IS:216 (not heated above 375 Deg.F) using not less than 1.5 kg. per Sq.M. When the first coat has completely dried up, the second coat is applied in the same manner using not less than 1.25 kg/m2 , in case of coal tar and 1 kg/m2 in case of asphalt.
Immediately after application of the second coat and before it is dried up, sand is spread on the surface to cover it completely. Sufficient time is allowed after spreading of sand before backfilling is done in order to allow the final coat to dry up completely.
Bitumen Felt : Application for Tanking
Bituminous felt is used for laying the waterproof course on the outside and inside of the walls and bases of structures. The material of this method should conform to IS:1322, and the workmanship to IS:1609.
The bitumen felt should be hessian base and/or fibre base as specified in Drawing/Schedule of items. This type of waterproofing are generally done by specialised firms.
Read Waterproofing by Polyethylene Films