Resin Bound Knowledge Base
Resin Bound Knowledge Base
Information - Whitening & Blooming
In some cases, the surface of a resin bound installation can appear to go white and this is commonly referred to as ‘blooming’. There are two common types of whitening (blooming) that can occur and whilst the underlying cause in both cases is water, the reasons for the white appearance and ability to repair the issues are very different.
● Urea reaction whitening
If water is allowed to enter the resin prior to, or during the mixing process this can react with the isocyanate component of the resin. When a resin bound system is mixed correctly (without water entering the mix) the resin component reacts with the isocyanate component to form a ‘polyurethane’ which is clear and has very strong, slightly flexible properties. If water is allowed to enter the mix this can react with the isocyanate and instead of producing the desired polyurethane it will produce a ‘urea’ which is white and brittle. This can also produce CO2 within the resin surface and result in bubbles which are white in appearance.
● Diffuse reflection whitening
If a resin bound surface has been laid and it rains before the curing process can sufficiently protect it, small craters and ripples can make the surface appear white. The whitening is in-part a urea reaction combined with a diffuse reflection. When light hits a smooth resin surface its reflection is specular and appears clear (fig1). When light hits a rough surface with micro-craters it results in a diffuse reflection which appears white (fig2). The affect is comparable to that of perfectly flat water appearing to be transparent whilst rough water is opaque.
The type and extent of whitening can all be affected by the quality of resin, type of aliphatic isocyanate, system ratio (index), curing stage (catalyst level) and the volume of rain that has impacted the surface. If a resin bound surface is impacted by rain prior to curing then providing the strength of the matrix is undamaged, it is often possible to repair the whitening by applying a coat of StarScape RESTORE. This is a very hard-wearing product formulated to both increase the overall strength of the bound surface and level the surface by filling textured areas and micro-craters (fig3). Although allowing water to access an uncured resin bound surface should always be avoided, StarScape ULTRA is supplied with a nitrogen blanket and has been formulated to specifically and vastly reduce the chances of whitening.
Over three years of formulating and testing has allowed us to create our unique system which reduces the likelihood of whitening through a combination of moisture scavengers, index balancing and proprietary technology.
● Moisture Cure & Dew Point
Whilst moisture should never be allowed to enter the aggregate or components of an uncured resin bound surface, atmospheric moisture (often referred to as the dew point) actually plays an important role in the curing and strength of the system. An excess of moisture will result in a reaction that creates a urea and this will be white and brittle however, a small amount of moisture cure is actually beneficial to the full strength of the system. This is accounted for in the chemistry and as such, in normal temperature conditions (Above 5°c) atmospheric moisture cannot be too high. A correctly indexed system such as StarScape ULTRA uses atmospheric moisture as part of its back end curing to increase the full cure strength. Only a poorly formulated system would not allow for a small degree of moisture cure and allow atmospheric moisture (dew point) to cause whitening or blooming.
StarScape ULTRA will not suffer from whitening or blooming because of a high or low dew point in the UK.