I am constructing a building from reinforced concrete and AAC blocks in Indonesia.
The building will have a flat (2% sloping) roof of reinforced concrete. This will be exposed to tropical rain, as will a overhanging canopy. It will also have foot traffic, leaves, detritus, etc.
I understand that it is important that the roof not leak, in order to avoid water entering into the building, and the canopy also not leak, in order to prevent the rebar rusting and failing over time.
As the roof and canopy are yet to be constructed, I may have the choice of coatings after pouring, concrete additives/modification as part of the pour, or both.
I can find in terms of coatings:
- 'waterpoofing slurry' based on resin modified cementious material (this is supplied as a bag of cement-like powder with a solvent) – this needs to be protected by cement screed as it is not UV stable
- waterproofing mortar – (cement to which water is added)
- ' a cold applied, one component waterborne liquid applied
waterproofing membrane', a 'Polyurethane modified Acrylic Dispersion'. Apparently this may also enhance solar reflectivity. There is an optional 120g weight polyester fleece, which is a polyester fleece product, you can apply at the same time. - A combination of non-woven polyester membrane, and 'UV-resistant acrylic emulsion'
- " one component, liquid elastic waterproofing coating, based on styrene-acrylics copolymers in aqueous dispersion reinforced with fiber to increase the tensile strength of the product. It forms a flexible, waterproofed and durable film layer"
- ATACTIC POLY PROPYLENE (APP) MODIFIED BITUMEN-BASED WATERPROOFING MEMBRANE
WITH NON-WOVEN POLYESTER FELT REINFORCEMENT WITH SAND BROADCAST (i.e. you melt bitumen onto the roof, and there's sand on top) - self-adhesive, rubber modified, bituminous sealing tape – this is a roll of tape, so I guess you would not use it for a whole roof, but only for small areas
- steel corrosion inhibitor – surface-applied (for the canopy only, which technically doesn't need to be waterproof)
Or concrete admixture:
- Watertight/superplasticising (HRWR) concrete admixture (Combination Fatty Acid and Polycarboxylate )
- Crystalline admixture
What's the best way to go? It seems like an admixture might save time and effort? But is it sufficient?
Best Answer
I would use the HRWR admixture to help seal the concrete. Alone, it might not be the best roofing solution, but it's well worth the minor cost for the extra protection.
The biggest problem that I heard was foot traffic. Normally I would recommend EPDM, but I'm not so sure about foot traffic. This sounds more like a terrace, in which case, silicone cement is most commonly used.
However, something like a layer of asphalt would be more durable. This could be layered over steel. I would consider using coal tar (sealer) on top of the asphalt (which works better than bitumen/petrol tar) for shedding water. However, using coal tar is against roofing codes (causes cancer) in most of the world.
But one alternative that was not mentioned would be a green or living roof. I don't really know much about the materials involved, but in a tropical climate, it might be best to just go with the flow (in a sense). Fighting the elements can sometimes be harder than working with them.