Marks on new pre treated slate

[Raechel]

Can you help we've just had black riven slate fitted, we are grouting and sealing and we have used LTP Grimex to clean and waiting for it to dry before sealing, but we have these white marks - would anybody be able to advise how to remove? Or will the sealer darken these spots? Any help would be greatly appreciated. Thank you

 

[Tile Shop]

Seen these blotches before a few times. Last time i looked into one of these queries we narrowed it down to be a calcium carbonate deposit. Another previous experience was pyrite iron which had a more metallicy lustre to it.

Anyway. Both times, LTP Grout stain remover was the most effective. Its an acidic cleaner that breaks down both of these minerals. It will require a good scrub with a black emulsifying pad. This will take most off the surface but bare in mind there may still be some remaining within the slate that cannot be completey removed.

Go straight in with the neat solution. As soon as it comes into contact, it will fizz white. Scrub it, leave for 10 minutes, scrub again, rinse, leave to dry, repeat if required.

Once done it will need resealing.

Thats my method but @Lithofin BOB is a genius at this stuff and may have some other solutions.

 

[Lithofin BOB]

As above with Paul , my only comment is to test both the product on an unlaid slate to determine the suitabilty of the product to the slate ( doesn't matter If there is no salt build on it ) , it may remove the mineral salt build but may lighten the tile. Also test the black pad again on an off cut first as this can scratch some slates, try a stiff brush or possibly a white pad , let the product do the work. Ensure any product you use is specific to slate, above sounds good or similar😉