Grouting and cleaning flags

[ToneAdo]

I have recently laid some Indian sandstone flags at the back of my house and now need to grout them. There are some marks on them from the cement we used as a bed, and I was wondering if anyone has any sage advice for how to approach removing these? Are there any good products on the market, or is good old fashioned elbow grease the only way? Also I have bought some Romex to use a a grout, and not sure if I should clean them and then grout, or the other way round?

Can anyone help?

[London Stone Paving]

I would clean them before grouting. You can remove the cement stains using lithofin builders clean. Its an acid based product so tread carefully. Dilute it strongly and if you need to increase the dosage do it slowly

[ToneAdo]

Thanks, that's good advice. What sort of dilution would be suitable - do you think 1:10 would be OK?

[London Stone Paving]

Start at 1:10 and increase if required

[ToneAdo]

Thanks. What could this product do to the flags if applied at too low a dilution? As it's acid based, would it permanently damage and mark the flags?

[London Stone Paving]

Indian Sandstone is hardy stuff. I have seen acid applied neatly before and cause no permanent damage but I wouldn't reccommend it. Stick with the 10% initially and increase by increments of 10% if required.

Just in case anyone else is reading the thread and thinking that acid based products can be used on all natural stones.... THEY CANT.

Under no circumstances use acid based products on any Indian dolomitic limestones, they will be completely ruined if you do. Always take professional advice before using any kind of chemicals on natural stone.

[ToneAdo]

That's fantastic - thanks for your help.

[lutonlagerlout]

always best to test any sealer or acid based cleaner on a spare flag or an out of the way area
LLL

[jonnyboyentire]

I agree with Steve. Good advice. One of my suppliers told me of a client who rang him recently, they supplied over a 100 m2 of black limestone last year. Client returned home after a break at the end of an extension project. Builder had left a note saying patio all cleaned and sealed for you now that we are finished. Client looked out of the window next morning to a blue patio

[London Stone Paving]

There are 4 Indian limestones readily available in the UK which acid will make a real mess of:

Black limestone as Jonny mentioned
Kota blue
Kota brown
Tandur Yellow

Also many of the European limestones which are used for interior tiles are unsuitable for exterior use because of the acid rain we get in this country.