You might try scraping one of the green spots with a nail to see how deep it goes. Looks like they could be green paint flecks. Pick an unobtrusive spot before experimenting and wear eye protection.

Thanks for the replies. It is definitely not paint since it does not wipe or scratch off.

What did you use to clean the slate? It could be a mineral deposit either from the cleaning solution (if you used a chemical added to the water) or it could be a mineral deposit naturally in the slate that became apparant once wetted. I would consult with a stone expert before attempting anything further... but I have heard of oil being used to buff slate... it might have the ability to shine as well as make deposits like the green flecks either not happen or camoflague them by darkening the whole piece of slate... Ask an expert because I'm not one! Good luck.

The slate in clean form is the natural colour. Manufacturers cannot sell such slates with spots. So they polish the surface with coloured wax(black in this case). The finished product is a shiny polished slate. If you want to get back your original shade , just spray boot polish and buff the whole thing and after that apply wax coat and again buff it. Please use an electric buffing machine with a slow rpm of 4000 RPM.

Cheers

Naveen Nanda

DUBAI

I used Parker & Bailey Granite & Stone Cleaner to clean the slate, using paper towels and a rag. Interesting about the black wax @naveennanda57. There was a lot of construction debris around so I assumed this was all dirt coming off of the surface of the slate. I bought this tile and stone sealer: http://www.lowes.com/ProductDisplay?catalogId=10051&langId=-1&productId=50343102&partNumber=643486-71217-TSS+QT+6-1&storeId=10151&N=0

If I wanted to get the black color back, is there a product someone can recommend? Thanks.

Many cleaners are acids in diluted form, and if the surface is soft and reactive , will remove the surface layer of the stone. This causes permanent damage to the beauty of the stone/slate.

In order to restore the colour , you will need to apply an impregnating sealer which will darken the surface. NOTE there are 2 types of sealers- one which darkens the surface and second which leaves no trace on the texture/shade. These are wax based sealers , and if you buff the surface with an electric buffing machine , can restore upto 90% of original colour.

Cheers.

We regularly do these type of restoration in Dubai. A company in US called MARBLELIFE can help you out.

Navveen

It looks like if might be efflorescence. Aldon has a efflorescence treatment that works great.

I would look for an oil-based "enhancing" sealer at a local flooring store if you want a darker color. The sealer you have is probably a good general sealer, but is only meant to keep it from staining. If you've already applied it to the stone you'll also need to use a sealer remover(we use Aqua Mix sealer & coating remover) before trying the enhancing sealer since it won't be able to penetrate the original sealer. You should see it darkening right away, but it could need several layers to get more color saturation as the slate can absorb quite a bit of it.

Not sure how to treat the spots though. Efflorescence is generally white, your spots looks more like a patina on copper, which makes me think it's something in the natural in the slate reacting with one of the products you've already applied.

Yes ,because slate is a natural product , it has tendencies to have imperfections.These can be minimised by having a high gloss( shiny) finish.