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Resin Bound Knowledge Base

Resin Bound Knowledge Base

Information - Rusting (Oxidation)

The aggregates used in decorative resin surfacing applications are natural products obtained from quarries. Whilst every effort is made to remove any metals from the aggregates trace amounts of iron can be found in some of the aggregate types and when in contact with air and water, the iron will react. 

When iron reacts with oxygen it forms a chemical called hydrated iron oxide (rust) because it has been oxidized (the iron has lost some electrons) and the oxygen has been reduced (the oxygen has gained some electrons). 

If an aggregate containing trace amounts of iron is used within a decorative surfacing resin it can result in ‘Rust Spotting’. Rust spotting is a small area (usually the size of a pound coin) on the surface of the cured resin which discolours to an orange/brown. Due to the natural properties of aggregate it is not possible to guarantee against oxidation. The image below shows a typical example of rust spotting and the chart on the following page shows the potential for each aggregate that may contain ferrous materials which can result in rust spotting:

Hydrated Iron Oxide
Resin Bound Rust Spot

It is important that a potential customer is made aware of the natural, hand applied elements of a resin bound surface as these can often be seen as a product or application failure.

A ferrous content in aggregate does not necessarily imply it will result in rust spotting however it is a good indicator. With many of the darker coloured aggregates rust spotting will be less visible and not present a problem when used on its own however when creating a blend with lighter aggregates consideration should be given to the impact of introducing a darker aggregate with a potential for rust spots. Example: Dunster black is highly likely to have rust spotting however these are not visible due to the colour of the aggregate. If this was combined with a light aggregate which does not rust, the rusting can spread from the black stone to the lighter coloured stone.

Resin Bound Ferrous Content