What we have learned about the whitening of EPDM flooring
30. June 2022
One of the visual defects you may find on an EPDM rubber surfacing job is the whitening on top of the initial colour after some time, usually a few months. There are some colours that seem to be more likely to have the problem, and normally you can find this anomaly mostly on lower quality EPDM. Luckily the products we sell at CONICA are among the best quality and we do not face this claim when we supply the EPDM.
We will try to explain in easy terms what we have learned about this problem, and for that we need to also review how the EPDM granules are manufactured. Don’t expect a scientific paper here, we always prefer to find easy explanations.
The EPDM granules we use in our flooring installations are EPDM compounds made up of 4 main ingredients: EPDM virgin Polymer, fillers, plasticizers, crosslinkers, pigments and auxiliary miscellaneous materials. The mixing is normally made in a continuous process using a Banbury tm pressure and temperature mixers or other variants of kneading machines
The formulation may contain between 20 and 30 inorganic or organic components.
Additives serve a variety of purposes for example to reinforce using carbon black, antioxidants, and UV stabilizers to protect the polymer against atmospheric conditions, flame retardants, accelerators for the vulcanization curing process as sulphur or peroxide and other ingredients with different goals.
The main fillers used are talc, calcium carbonate and “Kaolin” clay.
When you see a spot that is whitening you already guessing that it is all about the filler that is usually white or pearl coloured, but how is this happening?
We have discussed this internally at our team and there are two potential explanations:
One of them is, according to a 2012 scientific study we found recently, that the whitening is independent of the type of filler used and is due to the formation of calcium stearate, because of the reaction between the calcium of the filler in humid atmosphere or the calcium present in the tap water from irrigation or cleaning and the stearic acid. The stearic acid is coming from some of the plasticizers used on the EPDM mixture.
The other potential explanation is that filler is released after some exposure to UV radiation, creating this “whitish” surface.
Whatever the reason, as the chemical composition and properties of the pigments are different among them, there are colours that may be more prone to this whitening than others. The UV stabilizers used in the formulation are destroyed during exposure to this radiation and this happens more quickly with bright colours (orange, yellow) than with others. Using an aliphatic topcoat would help to delay this progress.
I think a good and tested formulation with selected good quality raw materials combined with a well-controlled and monitored process for EPDM mixing and vulcanization will ensure a more permanent mix of all components and avoid this migration of the filler that will show white areas in your flooring, whatever the end reason is for that to happen.
As usual the cheapest product at purchase time may end being the most expensive in the end.
- Robert Dickstein – Technical Rubber Course – June 2003
- EPDM Membrane Production: Materials and manufacturing process
- Journal of Applied Polymer Science – Volum 123, Issue 4 – Sung-Ho-Ha, Hye Seung Chung, Yong Tae Joo and Kyung Mo Yang – South Korea – February 2012
- Granulogy: Success based on knowledge of rubber – Gezolan AG.