Hardboard is a sheet product, usually 3mm thick, composed of pressed and glued wood fibres. For flooring this was used to cover a wooden subfloor prior to installing a new floor covering, although it is often not recommended these days.
A flooring installer might refer to hardboarding an area prior to fitting, however this should be taken with caution as the British Standards do not recognise hardboard as being sufficiently stable for the installation of any floor covering.
Only flooring grade Plywood (marked FG1 or SP101) is recognised for use on wooden subfloors prior to installing a floor covering therefore this should be the preferred option. The exact thickness will depend on the product being installed and the condition of the subfloor.
The honest answer is you could, depending on the condition of the subfloor, use hardboard without any concerns. The risk however that if the hardboarding fails, most flooring manufacturers would not accept any fault to their product as the British Standards were not followed.
We have only mentioned wooden subfloors in this article as these solutions are not relevant to concrete subfloors. Look for a future article on Smoothing Compounds that will explain this.
At Grimley Flooring we always carry out a survey of the subfloor as part of any in-home consultation and can recommend the appropriate way forward for the flooring being installed. Our advice is always to conform to the manufacture guidelines for installing their products and to follow British Standards. By doing so you greatly reduce the risk of anything going wrong in the future, as well as ensuring faults are correctly identified and rectified.