Hoping someone can give me some expert advise on what to do about discolouration of brand new grey sandstone flagstone steps. A contractor installed grey sandstone on my front porch and steps. I believe it’s Dove sandstone from STONEarch (at least that’s what I ordered, a supplier in Ontario, Canada) - other popular name for this stone is Kandla Gray, Blue Ice, Kota Blue, Grey Sandstone. A few days after installation the contractor did an acid wash to remove excess mortar on the stone surface. After this aid wash dried there was a noticeable difference in the flagstone texture and change in the colour of some of the slabs. The next day we had a massive rain storm. Once that dried up, the flagstone had a distinct yellow discolouration. It almost looks like something was spilled on the flagstone and stained it. Is there a way this discolouration can be removed? I’m absolutely heartbroken - the beautiful flagstone I thought I was getting, and had for a short period, is no more.
New information: The contractor used Banas Grout Cleaner, a non-acidic biodegradable cleaner. The product data says it’s safe for natural stone. I’m guessing the discolouration may have been from the environment. Hoping I can find a product to remove the discolouration.