Technical Guide
Waterproofing Roofs & Terracese's
Efficient waterproofing of roofs and terraces can be achieved by adopting proper construction practices. For a tropical region with heavy rainfall, (like Bombay or places on the west coast), a 'Weathering Course' typically consists of an insulating layer with an integral or separate finishing layer of IPS and a waterproofing course suitably located or laid directly over the R C slab. It is essential that no rainwater stagnates on the roof. A proper slope and adequate number of drainage outlets can achieve this. The requisite slope is obtained by varying the thickness of the insulating layer. Or when the roof slab is large in area, the slope or fall is often provided by making it's (the slab) top surface sloping to the desired extent.
A typical waterproofing system also referred to as 'Weathering Course' is shown below:
1. Finishing layer:
This could be IPS or China Mosaic or other treatment.
2. Lime Concrete or Burnt Brick Coba provides an insulation effect. Other lightweight materials like vermiculture concrete or P U foams can also be used.
3. R C Structural slab.
4. Vata.
5. Coping.
6. Throating.
7. Waterproofing layer:
Polymer based chemicals and cement layers form a membrane virtually.
The Method of carrying out efficient waterproofing using a 'Polymer - Cement' composite layer (Based on Polymer based chemicals) is given below:
A. For New Constructions.
B. For Existing Terraces.
(A) NEW CONSTRUCTIONS
When it is intended to carry out the waterproofing of a newly built reinforced concrete roof, it is best to provide the waterproofing layer directly on the structural slab. The insulation layer and the finishing layer can then follow.
Waterproofing Layer:
To obtain a sound waterproofing layer please follow the following procedure.
i) Clean the surface of all loose particles, dust, cement laitance etc.
ii) In case the slab is uneven and undulated it is desirable to make it level and smooth using a thin cement sand mortar. Use a 1:3 cement sand levelling and smoothening course not more than 10 mm thick. Alternatively neat cement punning can be considered.
iii) Moisten the R C slab (or the leveling mortar)
iv) Apply slurry of Polymer based chemicals and Cement, in the ratio 1:1.25 for first coat and for the subsequent coats 1:1.5 (by weight). The slurry should be freshly prepared, uniform in consistency and suitable for brushing (Consult our Engineer for details)
v) Apply 2 more coats at 24 hour intervals each, when the already applied coat would have set & hardened.
vi) Allow setting for 48 hours.
vii) Cure the coating with wet squeezed gunny bags.
viii) Finish the surface as per requirement.
Note: In case the roof is a sloping one, then the Polymer based chemicals -cement Slurry should be applied over the top of the slab. Finish as required is to be provided.
(B) EXISTING TERRACES
It is necessary to inspect the existing roof terrace and assess the reason for the leakages.
Generally the leakage's may be on
(a) account of the failure of the IPS or China Mosaic,
(b) the cracking and failure of the insulation layer,
(c) the failure of both.
(d) Defects or distress in the R.C.C. slab.
For case
(a) follow the steps given below
(i) Remove the finishing layer of IPS or China Mosaic totally to expose the insulation layer.
(ii) Clean the insulation layer
(iii) Provide a 1:3 cement-sand leveling and smoothening course less than 10 mm thick. Alternatively neat cement punning can be considered.
(iv) After the layer in
(iii) Has hardened say 24 to 48 hours, on the wetted surface, apply Polymer based chemicals and Cement slurry in the ratio 1:1.5 by weight (Consult our Engineer for details)
(v) Apply 2 more coats at 24 hour intervals each, when the already applied coat would have set & hardened.
(Vi) Cure with damp gunny bags.
(Vii) Finish as required.
For case (b) & (c) follow steps given below
(i) Remove the finish layer & insulation layer, to expose the structural reinforced concrete slab.
(Ii) Clean the slab and inspect for cracks and defects.
(Iii) Seal cracks if any with Polymer rich cement mortar (Consult our Engineer for details)
(iv) Level and smoothen the surface with 1:3 cement mortar about 10-15 mm thick.
Follow the steps (iii) to (viii) as in the note on (A) New Constructions, above.
For case (d) follow the steps given below:
(i) Identify and mark out the defects - viz. cracks, honeycombing etc.
(ii) Repair the cracks with Polymer Rich Cement Mortar. (Consult our Engineer for Details)
(iii) Grout the honeycomb areas with Polymer Cement Grout (Consult our Engineer for Details)
These steps will restore the slab to as near the original condition as possible.
PRECAUTIONS
1. See that the invert (lowest level) of the drainage outlet is BELOW the level of IPS in its vicinity
2. Provide one outlet for every 200 sft. (20 Sq M) of terrace area.
3. Provide a fall or slope of 1 in 50 for the top surface so that water is quickly drained out.
4. The Polymer-Cement waterproof paste or slurry using Polymer based chemicals, should be continuously stirred to a uniform consistency even during application.
Note : This Guide is by way of suggestions only.
The Consulting Engineers views should be sought