Strange marks on brand new blue black slate tiles

[Pajohib]

I’ve just finished laying my first patio using blue black slate tiles from Nustone. When I’ve cleaned the tiles up before sealing, I noticed a few of them have strange circular marks and at a glance they look like silver spray paint, which I doubt very much but that’s the appearance.

I’ve scrubbed them for ages and there’s no way they are coming off with elbow grease so I was really hoping for an opinion on what they are and how to remove them.

I’ve taken photos but don’t see a way to post them on here. Then again I’ve just joined this forum and might be being a bit thick. I’d be more than happy to share the pics by email if anybody thinks they can help.

Cheers,

Paul

[KeburDave]

You'll really need to put some pictures up so it can be ascertained what it is, the only markings we've had with Chinese Slate is the appearance of Calcium Carbonate, limescale deposits, they can appear circular, whitish blotches over the paving. If this is what it is we use a product called Drytreat Eff-Ereza to remove them, dilute it down, spray it on and it fizzes away, scrub then remove with water.

[Pajohib]

Thanks for the reply, I’ve added photos here:

https://drive.google.com/open?id=10uAYjpBHY8DkbBGs0TctQMKU4443jmZn

Hopefully they can be accessed? Now, perhaps naively I’ve sealed the tiles in the hope that the sealer would hide the marks to some degree at least. I realise that probably wasn’t my best idea ever. If I have to live with the marks I will but I’d rather not given the effort that’s gone into creating a good patio!

[KeburDave]

Yes that's definitely calcium carbonate (limescale) the product I said would have removed these marks, unfortunately sealing it, I don't think you'll remove the marks without stripping the sealer first, what product did you seal the slate with?

[Pajohib]

I used Lithofin Stain Stop & Colour Enhancer to deal it, is it worth trying the product you’ve mentioned anyway or am I likely to cause a right mess!?

[Pajohib]

Seal not deal!

[KeburDave]

Not sure, the Eff-ereza will possibly strip off the Lithofin sealant, so you might need to re-seal after, I've got a slab here with the calcium carbonate on it, ill run a little test of putting Drytreat Intensifia (Colour Enhancer) which is a similar product to the Lithofin and then apply the Eff-ereza after and see if it removes the stain. If it works you might want to test one slab first apply the Eff-ereza, if it fizzes away, agitate, then clean off with water. Then once dry apply the Lithofin sealant and see what the result is.

[KeburDave]

Hello Paul,

I've just ran a small trial here at Kebur and after applying the impregnating Intesifia sealer to the slate with the limescale deposits I have then applied the Eff-erayza remover, it did fizz up so I've agitated/scrubbed the slab with a stiff brush, and removed with water and a cloth and the stain has gone so I think the Eff-erayza would remove your stains. The product is only around £25 so its probably worth trying it on at least one slab and see the results for yourself. Your pretty safe with slate as opposed to limestone's or some sandstone's in the fact that you will not etch or damage the slab. Cheers

[KeburDave]

My Webpage

If you click on this link it will show the before and after photos of the trial

[Pajohib]

Hi again,

I cannot open the link you’ve posted but I wanted to say thank you very much indeed for going to the trouble of doing a trial for me. That was very good of you and very much appreciated. I’ve never laid a patio or used slate in my life so it’s really great to get advice from somebody who knows what they are talking about!

I’ll give the Eff-erayza a try and thanks again for your help

[KeburDave]

No worries Paul, not sure why the ink won't open but if you wanted to email me at landscapedivision@kebur.co.uk I can send you over the pictures of the trial, cheers Dave

[George-Stone Gardens]

Sorry - jumping into this thread. Can anyone tell me if they think the 'ripple' effect in this slate paving is also limescale/efflorescence or just a character of the stone?

Slate Pic