Common Wet Pour Issues
The Yellowing Phenomenon
Unfortunately with all MDI based, aromatic binders, that are mixed with EPDM synthetic rubber products, there will be a yellowing effect to a greater or lesser extent.
After a period of time however, depending on the intensity of UV/sunlight, this yellowing will disappear. The time scale could be, in our experience, from 6-20 weeks.
What actually happens is that with both factory-made playground tiles and in-situ playground surfacing, there is a very thin film of binder on the surface of the finished product. As the binder is straw colored it tends to darken and appears to change the color of the EPDM, albeit temporarily. The colors most affected are usually light blue, beige, grey, eggshell, purple and white.
Nevertheless, once this “film” has been burnt off, the colors will return to their original shade, but this may take time, as already stated, several months depending on the UV strength of the sun.
Furthermore this “yellowing” does not affect in any way, the integrity of the tile or in-situ installation and is a totally different subject from EPDM color fading.
For clients who do not wish there EPDM surface to go through this “yellowing” phase or if the surface is located in an area of uneven UV exposure, aliphatic binders can be used which are not affected by this phenomenon. There are quite major cost implications with this option as aliphatic binders can be 3-4 times more expensive.
Chalking occurs when the wet pour surface is exposed to UV/Sunlight over time. The surface may appear to have a white coating or the colour of the EPDM may seem faded, but disappears when wet. The chalking may also be more noticeable in areas where the UV exposure is uneven.
This will happen on all coloured EPDM surfaces as a result of natural aging and sun exposure.The extent of the chalking varies however, depending on the EPDM granules used, the binder used and environmental conditions.
- EPDM – Each EPDM manufacturer has their own formula for producing the EPDM granules typically found in wet pour applications. The pigment types used, polymer content and quantity of fillers used can all have an impact on the degree of chalking.
- Binders – Most wet pour surfaces are installed using aromatic polyurethane binders, these binders absorb UV light strongly and undergo photo-chemically initiated degradation which can lead to yellowing as discussed above but also chalking in the long term. Aliphatic polyurethane binders can be the answer to this as they do not absorb UV light, however, the cost is often prohibitive.
- Environmental Conditions – These include pollutant exposure, how exposed the site is to various other weather conditions and the number of hours each year the site is exposed to UV/sunlight. As an example, a surface in a sunny area in Spain will generally chalk much faster and to a greater extent than the same surface in a sunny area in England.
When considering which brand of EPDM to purchase for a project it is important to check if the granules have been tested with regards to UV exposure, this is normally done in a QUV machine to show accelerated aging but can also be done naturally outside using cast tiles of EPDM and binder.
If you would like a copy of our QUV test results, please request one via the contact page.
De-lamination, Crumbing and Hard spots
These type of problems generally stem from too little/ too much binder respectively and can be exacerbated if the wet pour slurry is poorly mixed.
It is essential that short-cuts are not taken in this regard and the correct amount of binder must be used in the wearing surface, we recommend 18-20%, and that it is properly mixed in a forced action mixer.
Shrinkage is the appearance of gaps between joint lines on the top wearing surface or between the top wearing surface and concrete border kerbs. It is important that all cut surfaces need to be primed prior to closing up with another colour to ensure the newly cut area has the “key” to hold strongly at the joints.
Migration of the plasticizers can cause shrinkage over time so it is essential to ensure the wearing layer is laid at a reasonable depth. 15 to 20mm is normal practice in the industry, the thinner the wearing layer the more prone it is to shrinking.
Please see the gallery below for examples of the issues discussed.