discoloured / damp slate tiles

[Gezzamuzza]

My kitchen has slate tiles there are a couple next to the washing machine which are discoloured - see photo (top right tile). I'm worried this might be a sign of water underneath them, one of them is a bit loose.

I've checked the washing machine and there are no obvious external leaks.

Has anyone else seen this before? Or have any advice how to remove the marks?

Thanks lots

 

[Alastairreid]

View media item 12818
http://www.tiledoctor.eu/Slate.html

 

[Gezzamuzza]

Thanks Alistair, I'll be purchasing some soon.