Cement residue removal from sandstone

[willyboy]

Hi all

I've laid about 45 - 50 m2 sandstone this week in my garden. Some of the barrows of mortar we mixed was a little wet and inevitibly I have got a fair bit or residue now on top of the slabs.

I tried to jet wash it off but only the really light stuff comes off. I know that acid is supposed to be a no no so was looking for some help or guidance on how to remove it. I haven't pointed the joints yet.

I have scrubbed up one or two tiles with a wire brush as I read that this would be OK and it seems to remove the reside but I have a hell of a lot to do.

Firstly, Is this a safe way to remove it? And secondly, is there a quicker way? Oh, and should I definitely remove it sooner rather than later, Ie before I do the pointing?

Many thanks for any help and advice

Chris

[RAPressureWashing]

Phosphoric acid, do a google search for Tiling Logistics, as they sell it. It is sandstone safe.

[willyboy]

Many thanks for this response - I have sent them an email and hopefully will hear back soon.

Would this be applied by spray for example and i assume i will still have to scrub it on/off? - if so, is the wire brush ok to use or will i mark the sandstone?

Also, should i do this before grouting/pointing or should i get all the pointing done, then let that harden for 6 weeks and then use the phosphoric acid on the whole lot? being a bit of a novice in this area, I assume i will probably make a mess pointing as well

Many thanks for you help and advice.

[RAPressureWashing]

Many thanks for this response - I have sent them an email and hopefully will hear back soon.

Would this be applied by spray for example and i assume i will still have to scrub it on/off? - if so, is the wire brush ok to use or will i mark the sandstone?

Also, should i do this before grouting/pointing or should i get all the pointing done, then let that harden for 6 weeks and then use the phosphoric acid on the whole lot? being a bit of a novice in this area, I assume i will probably make a mess pointing as well

Many thanks for you help and advice.

NO to the wire brush, use a nylon one, you could spray it on, but you have to dilute the chemical anyway, read the instructions and follow them to the letter. I'd get the residue off that you have now to start with and try to keep the pointing as neat as possible and clean-up as you go along.

[willyboy]

Thanks for that. When you say no to the wire brush, can you say why? I tried it on a small area and it seems to have been fine? Appreciate you are the knowledgable one here but just wanted to know what negative effect it would or could have had?

[RAPressureWashing]

Thanks for that. When you say no to the wire brush, can you say why? I tried it on a small area and it seems to have been fine? Appreciate you are the knowledgable one here but just wanted to know what negative effect it would or could have had?

Because there is a chance you could scratch the paving, plus you will be using an acid, if you go the phosphoric route and you are best off using a nylon brush they wire etc.

[willyboy]

Thank you for confirming the reason why.

However, this is contrary advice to that in the link below about removing cementitious stains? It also says that mechanical use should be tried prior to any chemical use?

http://www.pavingexpert.com/stains.htm

Is Indian sandstone not one of the harder sandstones though as i have used it and no scratching seems to exist? I did try and use a few other rather hard bristle brushes but none of them seemed to do any thing to the cement marks apart from the wire brush.

I have bought a Brass wire brush yesterday and therefore non ferrous metal to hopefully prevent any rust marks or anything - do you think i should not just go carefully with this first ?

i know i probably sound quite annoying to the the professional people on here so i apologise.

kind regards
chris

[RAPressureWashing]

The brass brush is a better option then a steel wire brush.
I did actually give you a safe option for the chemical usage for the staining you have, the problem is as soon as you say "use an acid" most folk or idiots use hydrochloric acid aka brick acid and this is where the problems start.