Thursday, September 8, 2011


New Roofs

Leakages in terraces occur through primarily three sources:

  1. Vertical horizontal joints.

  2. Honeycombs and capillaries in concrete.

  3. Areas of weak concrete cover e.g. over electric conduits are placed or areas where hooks for fans or false ceiling are placed.

The precautions to be taken in the case of the terraces are provisions of adequate slope and provision of adequate drainage. Both these however have to be done after the water proofing operation is over. These steps in the waterproofing operation are below :-

  1. Remove whatever surface treatment exists to expose the bare concrete. Undertaking the water proofing from above the existing treatment itself is totally non-feasible. If any coatings are put above the old treatments the same will either crack alongwith the cracking of the old waterproofing system or will get blown away when the air trapped in the mud fusca or coba below the coating expands in the intense heat.

  2. Using a hammer hit the concrete at regular intervals to find out the hollow areas. Also by observing the roof below identify the electric points and the likely route of the conduits. Also look for any cold joints that may exist due to concreting not being monolithic.

  3. Fix nozzles in the concrete as detailed before. Also fix at all weak areas where leakages have been noticed before and also at the areas surrounding the conduits.

  4. Injection grout the nozzles as before.

  5. Cut the nozzles with a saw. This will result in 5 mm or so of the nozzle protruding above the concrete.

  6. Make a haunch at the vertical horizontal joint over a coat of polymer slurry. The haunch should be concave since a convex haunch cracks more easily at the joint.

  7. Apply three coats of penetrating mineral coating.

  8. Provide slope to the surface with either lean concrete, or the mud fusca brick tile system prevalent in North India giving a slope of at least 1: 120.

  9. Provide adequate drainage exist points

  10. Lay cement plaster with 1:3 mortar if concrete is excessively segregated or defective. Also increase cover on points where it is lacking.

  11. Laying of drains in the case of a terrace garden is very important. Regular cleaning of the drains is an important point in the keeping of a terrace garden leakage free.

  12. Fill cracks in the existing roof, with a silicone or butyl sealant before starting the rest of the process.


Clamps driven into walls -
Chase open areas around such clamps etc and fill the same with a silicone sealant

Openings of drain in the side walls
Have a similar treatment to the point where the drainpipe carrying the water joins the terrace.
Holes in slab to drive drain pipes
Often the drainpipes are driven vertically through the roof slab that is an incorrect way of doing the same. Injection grout the concrete around the
Pipes and then seal them with a polymer mortar. Also seal round the edges with a butyl sealant.


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