Preparing for a Topping Slab

A concrete topping gives a finished floor surface a new look and increases its strength.  Ideally, concrete contractors will design the overlay top to provide a dense, abrasion-resistant floor surface. In addition, a concrete topping serves a multi-purpose use, which include supporting the traffic load in parking facilities or other heavy traffic areas.

What is the Purpose of the topping slab?

  • T\to provide the slab with adequate waterproofing
  • to ensure abrasion resistance to the underlying slab
  • to dd a wearing course that supports the load coming on the concrete surface
  • T\to ensure a level floor surface
  • to develop an additional superimposed load-bearing capacity

Different types of concrete topping slab:

1. unbounded topping slab

This system is where the topping slab is not bonded to the underlying concrete slab. The unbounded topping slab thickness may influence the final floor elevation and interfere with other service requirements like doorway clearances. In addition, if the cracks in the base slab are repaired in the process, they may eventually reflect through the partially bonded overlay. This reflective cracking could be reduced using thicker overlays.

The unbounded concrete topping is used for a contaminated slab and for slabs where bonding is impossible. This  topping is also used where it is preferable not to bond the topping to the base course. Therefore, the two courses can move independently or move at a later point in time.

2. bonded topping slab

In the bonded system, the topping adheres to the underlying concrete slab. Therefore, the bonded topping slab is used for both light-duty slabs in commercial applications and heavy-duty slabs in industrial applications. The application area largely depends on the traffic loads\.

The base slab surface should be rough and feature an open pore finish. In addition, the base slab should be free of any substances that could interfere with the bond of the topping to the base slab. Note that the topping can be placed before hardening the base concrete slab or after the base slab has set.

Topping a light-duty slab features a concrete mixture similar to that for a concrete slab. You will require multiple passes for the heavy-duty slab, a hard-steel trowel finish, and higher strength compared to the base slab.

For bonded andunbounded concrete topping slabs, the strength of concrete is governed by the function of the slab. You can use reinforcements such as deformed steel bars, welded wire fabric or fibre. Thereinforcement selected is placed in the mini concrete topping to reduce the width of the shrinkage cracks.


Adding a topping slab is becoming a widespread redevelopment practice since it is cost-effective and aesthetically pleasing compared to other slabs. Generally, the topping slab is more sustainable and high performing, while it provides a more refined surface finish. Talk to a professional concrete delivery company to ensure good quality concrete for your topping slab.