The study emphasizes the effects of the formwork material that imparts a characteristic surface hardness to the concrete. Concrete cubes were cast of the M20 grade in different mold material like Cast Iron, Shuttering Plywood and Timber. The effect of these materials was studied by using the Rebound Hammer Test to find the Rebound numbers which depend on the surface hardness of the concrete. The results obtained are explained in the following statistical form. It can be concluded that each formwork material imparts a characteristic surface hardness to the concrete.