The impact sound ratings given here are for floors that have no finishing layer - no vinyl, carpet, parquet etc. In some cases the floor topping can have a large effect on the impact sound rating. Whether a topping improves, worsens or has no significant effect depends on the floor to which the topping is added and on the rating system being used.
The IIC for a bare concrete floor or one finished with hard tiles is determined by high frequency sound levels. These high frequencies are greatly reduced when a soft layer, such as vinyl, is placed on top of the concrete. This results in a large improvement in IIC for the floor plus the topping. The same vinyl placed on the wood subfloor of a joist floor will have no effect on the IIC rating for the floor. The impact insulation class obtained with the standard tapping machine depends on the combination of the topping and basic floor.
A lightweight floating floor system usually comprises a hard upper layer of wood or a dense wood fibre board (about 9 mm thick) resting on a fairly thin (about 5 mm) layer of some resilient material. Such toppings can increase the IIC by about 20 decibels relative to the bare slab. Applied to a joist floor, the increase will be small.
The IIC rating never applies to a floor topping or a resilient underlayment on its own. It always applies to a complete floor system.
Given two test results for two topping systems tested on different concrete assemblies in different laboratories, it is not possible to tell which topping is the more effective.
To compare topping systems for use on concrete slabs, tests according to ASTM E2179 Standard Test Method For Laboratory Measurement Of The Effectiveness Of Floor Coverings In Reducing Impact Sound Transmission Through Concrete Floors must be carried out. There is no ASTM test for evaluating toppings for use on joist floors.
More information on impact sound through floors can be found in CTU35: Controlling the Transmission of Impact Sound through Floors on the IRC web site.