Joined: July 2004
||Posted: 04 Oct. 2019,09:36
It's natural iron colouration/mineralization within the stone, and there's nothing you can do about it.
There is natural variation in most stones and, in the case of Kandla Grey, there are some seams or beds that have this higher density of iron minerals. Once exposed to the damp of the British or Irish climate, the iron becomes a rust, which then discolours or 'stains' the stone.
It doesn't affect every piece of stone. It may affact an entire flagstone, or it can appear as a patch or a small stain, and it's largely unpredictable.....but not entirely unpredictable.
What we see is that the top brands exhibit far fewer instances of this phenomenon than the bargain brands, which indicates that, somewhere along the supply chain, some gadgie with a keen eye is hiocking out the suspect pieces to create a 'first class' stock with few, if any, suspects, while the stocks intended for those buyers who are concerned only with price will either not be scanned and selected, and may even be 'bumped up' with the suspect stone taken from the 'first pick'.
While a good quality rust remover will shift the staining for a while, it more than likely *will* return. So, that leaves you with two options: either learn to live with the natural variation of the stone and accept it for what it is, or get the naff pieces replaced.
Site Agent - Pavingexpert