Topping Concrete

April 21, 2020

Topping concrete is defined as a layer of high strength concrete placed on an old to prevent a dense, abrasion-resistant surface, to increase structural depth and strength of the base concrete.

Evolution is required before the laying of topping concrete over an existing concrete surface. The existing concrete must be hard and strong.Weak and fragile concrete bases are not preferred as they don’t achieve adhesion between the old and new concrete. Preparation is the important step in laying of topping concrete. The surface must be uniform, clean and free from dust particles or other contamination. If the base concrete is finished smoothly then the surface must be made course by the help of mechanical scabbing or scarification machine, so that the course aggregate of the base slab is exposed. The loose debris, dirt and dust must be removed using a vacuum cleaner.

Before placing the topping concrete, a small amount of water is to be poured in the base slab and the absorption rate must be checked. If the water is absorbed in few minutes then the slab must be kept wet for 4 hours before placing the topping concrete and the water must be completely removed before just before placing.It is because once the wet concrete is placed in the base, all the water content of the concrete is absorbed by the base slab n the topping concrete is deficit of water. If no water absorption is seen, then the topping concrete can be laid as done in normal process.

The surface is first poured with the slurry made out of cement, sand and latex bonding agent. Before the slurry dries up, the concrete is placed. The concrete mix shall consists of aggregates, sand and cement depending upon the strength requirement of the topping.The topping concrete should be spread, compacted, screeded and bull floated as for a concrete floor.

The type of finishing required for the topping concrete depends on many factors such as place, usage and surface requirement. If topping concrete is placed on the existing slab, then it is given rough finish for laying of flooring material. If the concrete is placed on floor concrete it can be made as smooth finish.

Concrete has to be effectively cured if maximum surface strength, maximum resistance to surface abrasion and low impermeability of the concrete are to be attained, and the development of drying shrinkage cracks is to be avoided or minimised.

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