Possible acid damage to real slate flagstones - Spoilt patio/pathway slate

[gardener123]

We recently had our patio/pathway replaced with natural slate flagstones which were laid very well but unfortunately the pointing was done in wet weather.

Needless to say the whole of the face/area of the flagstones were covered with a cement film the following day upon drying out. The Company didn't come back to clean this for around 7 days. They were scrubbed with soap/water but to no avail. They then used Grimex an ammonia substance. Didn't work. They then used a few days later a mix with 10% hydrochloric acid. They scrubbed and scrubbed the slates and they ended up much paler than the original which we didn't really like. We then sealed with a sealer only to find when they dried out it appeared that a white residue was bleeding through. Absolutely ruined. White patches all over plus the fact that it brought rusty streaks which don't look very good. Presumably iron ore ?

We believe it's the acid coming through because we did manage to scrub 3 flagstones the day after they were laid and shortly afterwards sealed them. They had no chemicals applied at all. These have no white residue.

My question is. Any ideas what can be done now. The slates look dreadful.

Many thanks for replies.

[GB_Groundworks]

the milky white residue is general caused by moisture in the flag while sealing, have to have a long dry window to apply the stain and for it to go off.

edit: sorry typed staining instead of sealing multi tasking brain not in gear



Edited By GB_Groundworks on 1286481466

[gardener123]

Thank you for your reply. Apologies but don't really understand what you mean.

Is the white residue caused from the overspill cement staining, or coming from the actual slates, or have we sealed too soon? In either cases. Will it disappear with time ?

[GB_Groundworks]

sorry typo, white stains generally are caused by there being moisture sealed in by the sealer, either flags were still moist etc thats the most common cause of the milky staining, there is generally one person a week on here with same problem.

[gardener123]

Thank you for that.

Is there any way to overcome this or will it eventually disappear with time. Part of the patio is underneath a canopy/open porch.

[London Stone Paving]

You need to take some professional advice. The slate has now been exposed to cement, ammonia, acid and sealant. Thats a lot of chemicals. First of all stop using chemicals as you have no way of knowing how the slate will react.

Get in touch with extensive who are experts on stone maintenence.

Good luck

www.extensive.co.uk

[gardener123]

Thanks for the replies.
We are really disappointed now. We paid a lot of money for these slates and now they seem to be absolutely ruined.
We got in touch with the chemical suppliers and they told us to strip off the sealer via Grimex and then use their colour intensifier and stainblock. More chemicals !!!
We have used the Grimex and the slate is probably worse.Don't know whether to use the colour intensifier and stainblock. Any suggestions please ? Bradstone slate by the way.This has been a real saga and at the end of the day if the builders hadn't grouted/pointed in the pouring rain and left a huge amount of overspill cement on the face/sides of the slate then we wouldn't be in this situation now. Because they were pushed to finish they even laid the slate and grouted/pointed immediately after. This has cost us thousands of pounds.

[lutonlagerlout]

regardless of time no man worth a carrot ever points in the rain
i feel for you, all of us on here at one time or another have had a nightmare when a sudden shower occurs whilst pointing,but this sounds like a rush to finish
slate is well known for colour problems
roger oakey from R and A pressure washing is the man you need to speak to
do not apply anything untill you have had real professional advice from a man who can
link for R and A pressure washing

regards LLL

[seanandruby]

was wondering if a hot water jet wash might move the sealant.?

[gardener123]

Thanks for all replies and suggestions. We think the sealant is removed now that we re applied the Grimex but we're still left with masses of unsightly white blemishes. The slate looks nothing like the spares we have. They may have totally ruined them. Wish I could post you a picture for you to see the damage. Got the photos on computer but not really computer literate. You'd be amazed at the concrete spillages/overwipes. Scared to do anything more. Poor slates have been given a hell of a time ! and they're only thin slates i.e. 23 - 25mm thick so feel we can't do much more to them. May have to seek legal advice.

[London Stone Paving]

Mail the photos to me:

steven@londonstone.com

I will upload them on the site

[London Stone Paving]

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[London Stone Paving]

Its a shame because the installation looks good.

[cookiewales]

Its a shame because the installation looks good.

slate is not easy to point unless you know what your doing joints need to be smaller wrong coulour tone am sure roger could clean it dont worry if jointing comes out you could then use epoxy romex basalt ??? ps slate will stand up to a lot of abuse



Edited By cookiewales on 1286688731

[lutonlagerlout]

the installation looks ok ,joints are way to big
the pointing is rubbish
dont put anything else near it till you get proper advice
I know it may be tempting to have a go but dont
the bit mac looks a fair job
LLL