2. Performance of underlays in relation to the use of the floor covering
Floors are subject to different loads in different classes of use. The underlay must guarantee the integrity of the floor covering. On the other hand, the underlay itself must be able to withstand these loads without losing technical performance in the long term.
It is a general misconception that thicker underlays perform better in this respect. This is absolutely NOT the case.
Instead the absolute deformation under load is important. It is generally assumed that a maximum deformation of 0.5 mm for type 1 floorcoverings, or less than that for type 2 types, are allowed in order to protect the connection between the modules. Thicker underlays may behave negatively in this respect. Therefore the following characteristics are important.
The technical characteristics that influence the integrity of the floorcovering are listed below.
DL: dynamic load
Dynamic load is the pressure generated on the floor covering system by foot traffic, castor chairs, trolleys, etc…The underlay needs to be able to “absorb” these repeated loads of short Duration without losing its absorbing performance over time.
This capacity is expressed using the DL value. A defined load is applied on the underlay for a short time and then released. This cycle is repeated with a defined frequency. The DL value is the number of cycles to obtain a reduction of underlay thickness of 0.5mm.
The higher the DL value, the longer the underlay will withstand these dynamic loads.
Depending on the underlay group, different loads are applied, and therefore DL25 and/or DL75 have to be specified.
The floor covering has a significant effect on the load distribution. Depending on the floor covering, the underlay will be subject to different loads. Therefore, DL tests for group 1 underlays will be carried out applying a maximum pressure of 25 kPa, and for group 2 underlays with a maximum pressure of 75 kPa.
CS and CC: compressive strength and compressive creep
= Performance in relation to static loads
Sustained static loads on the floorcovering such as the weight of the floorcovering itself or heavy furniture standing on the floor (e.g. cabinet, piano, aquarium, etc.) may cause the underlay to be reduced in thickness over time.
Compressive strength (CS) is the force needed to compress the underlay 0.5mm in thickness.
Compressive creep (CC) evaluates which load can be put on the flooring over a reference period of 10 years until 0.5 mm compression is reached.
Case 1 – CS
Severe deformations may cause irreparable damage to the joining system and/or the core layer. This test determines the load necessary to put on the joint between the floorcovering elements, so that the floorcovering will be pressed down 0.5 mm.
The higher the CS value, the better the underlay will protect the joining system and prevent gaps, height differences, squeaking, etc.
Case 2 – CC
When an underlay is compressed by the static load over time, all beneficial technical characteristics, such as acoustical and thermal insulation, levelling capacity, etc., might disappear.
The higher the CC value, the more static load – e.g. heavier furniture – can be placed on the flooring system for a long period of time without losing technical benefits.