Normally, the top surface gets finished with thread lines to stop any possible crack from developing across the surface.
Ask any engineer contractor to list areas of concern and we are almost sure to find water seepage and terrace water-proofing to be among the top. From the very local solutions like mud layer poured with lime slurry, a traditional cost-effective solution, to the latest research on chemical-based methods have all been explored, yet no one idea stands out as ‘the’ solution. Possibly, we cannot list varied eco-friendly options here, but some cost-effective ideas exist and are in practice.
By far, the most cost-effective method appears to be treating the concrete roof on the same evening of concreting, when it is still not hard set. Thin slurry with one part cement, two part fine grain river sand and ample water to create the flow condition is poured on the top of the freshly cast roof. Then, starting at one end, the masons will work backwards, gently levelling and pressing the slurry into the concrete, filling its micro pores; wiping out the step marks and such other undulations using a square, flat, handled trowel. This slurry should become an integral part of the roof while the concrete is still being soft and ensure that the top layer becomes impervious. Water-proofing admixtures in liquid form can be added to the slurry to get better quality. Normally, the top surface gets finished with thread lines to stop any possible crack from developing across the surface.
While this top surface would survive most climatic conditions, topping the terrace with weather proof course (WPC) tiles has many advantages, despite the additional costs. The terrace is cleaned, applied with slurry mix of 1:2 and surface made rough by sweeping it with broom stick. A mortar mix of 1:4 is applied on top, as if we are plastering the surface, and the thin WPC tiles are fixed with 2 to 3 mm gap in between. The WPC tiles are made of burnt clay with two surfaces and small holes in between. Normally, these tiles are broken into two parts, and laid with the smooth surface on top. Water-proofing compounds are not required at this stage, though there are contractors who prefer using them with the mortar. The WPC layer protects the concrete surface from sun, rain and wind, giving it a longer life. The terrace becomes more usable due to the good flooring.
Many companies have been promoting methods and corresponding products of their own towards effective terrace finish. Most of them rely upon chemicals, polyurethane coatings and admixtures, hence tend to have a limited life span, though they guarantee the surface until then.
Every terrace solution comes with its own advantages and disadvantages. The practice of terrace tiles may not go well with heavy rainfall areas, unless quality of workmanship is achieved. In such cases, the simple method of plaster on the same day works better. In hot, dry climatic zones, this method may heat up the interiors more, the top being just a dense concrete layer. As such, it is important to seek local solutions to the terrace.