With my experience i will suggest you to go for waterproofing coating process.
How to waterproof concrete roof slab.
You can waterproof a concrete slab roof terrace by sloping the slab gently with mortar towards the roof gutter if there is any then sloping the roof gutter towards the downpipes such that the stormwater is adequately collected.
Topical sealers can be made from acrylic epoxy and polyurethane based materials.
Deciding which walls to waterproof and which ones to forgo can save you.
Apply the finish system you have selected to the wall according to the manufacturer s directions.
When waterproofing concrete a topical sealer is applied to the surface of the concrete.
Apply a suitable.
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Know which walls to apply waterproofing to.
Allow the vapor barrier to dry before you add a second coat.
In this process waterproofing chemical are used in different ratio mixed with any opc cement and applying different 3 4 layers on the slab you can also add fibermesh jalli it is a type of mesh made up pf fiber it helps to make strong bond with coating.
Overlap the previous line every time you start a new one.
Work systematically from one end to the other spraying in lines.