Natural slates changing colour

[Trimble]

I am hoping to get some advice!

I am building a house which I had slated with blue / black Spanish natural slate last October. When the slates were put up I was delighted with everything. Recently however I've noticed a lot of the slates on the Southern side of the house in particular are changing colour (about 1 in 10) to an earthy brown (reaction to sunlight????), . There is also some evidence of orange rusting, even though copper nails have been used throughout. I have seen two other house where the slates were used and they are now experiencing the same problems. Again these slates were fine when first put in place but are changing colour. None of these people have approached the supplier yet.

What I need to know is: why are the slates changing colour?
What are my rights when I go back to the supplier? And what can I get him to do bearing in mind I have paid for the slates in full?

Any suggestions / ideas would be most welcome. Thanks!

 

[puffin]

Would it be possible to let me know who supplied your slates. We have been looking into getting spanish natural slate as we thought they would be of good quality and not change colour. I was shown many slates by a Capco rep and he assured me of their quality. The only thing was some colour change (green)on North facing side due to our weather conditions and shading. Their Spanish slates looked pretty good where I had seen them but they were only couple years old.

 

[Roundy#]

Pyrites can be found in some natural slates, especially the poorer quality ones - like small specks of iron - with the onset of rain they will rust and cause green streaks to run from them.........

 

[Trimble]

Thanks for your replies!

The slates I used were not from Capco.

I was aware of pyrites and had asked the supplier about them. As I said there is a small bit of rusting but the main problem I have involves the complete slate changing to a earth/brown colour!