How to clean concrete from flagstones

[whathaveidone]

Hi All,

Finally after many many months we have moved into our property.

First thing to be removed was an old stinking carpet along with its underlay.
The plan was to replace this with a vinyl, but to our delight, under the underlay were flagstones.

The previous owns at some time have "filled" some of the indents with a concrete based material, and the edges have had a latex type of levelling compound poured to get a smooth base.
We are keen to restore the flags, the latex is easy to remove, a small tap with a hammer and it shatters.
However the concrete is proving to be a bit more troublesome.
They have also applied a tar to some of the joints.

I don't want to do anything to damage the stone underneath, so looking for recommendations on the best way to this.

Thanks,

Paul

 

[paulc]

I've used hydrochloric acid (HCL) before now to clean cement residues off brickwork - You can often find it sold as patio & concrete cleaner.

A couple of words of warning. It gives off unpleasant fumes, so provide plenty of ventilation and/or wear a respirator. Keep a good supply of clean water close at hand, and don't splash skin or eyes (again, wear goggles & rubber gloves).

HCL will remove ingrained cement, but any lumps will need to be gently ground down. As always with any cleaning compound, test a small inconspicuous area first. That said, if the flags are limestone, acid will be the last thing you'll want to apply.

 

[Greg.Hobson]

The plan was to replace this with a vinyl, but to our delight, under the underlay were flagstones.

I have nothing of value to offer, but did ask myself whether I was the only one to do several double-takes at the above (my underline) and add the word "Caramba!" on either the beginning or end?

Sorry.

Back to topic . . . .

 

[GPHouse]

Hi

I assume they are Limestone flags?

In that case acid is bad idea I would imagine. The reaction between Acid and Limestone will be interesting... lots of fizziness...

Limestone + Acid -> Calcium +CO2 + Water

I suspect it will do more damage than good!?!
G

 

[GPHouse]

I did speak to a builder about something like this the other day.

While a WAY more destructive than I would ever use, he mentioned he had previously used a type of flail / Scarifyer which took of the top layer (in an irregular fasion keeping some character, and then he used a combination of belt sander and diamond polisher to finish the stones. Apparently it worked....

Not other ideas im afraid

 

[whathaveidone]

Thanks All for your comments.

At the moment I have been taking the hammer approach, most of the concrete breaks away from the flag, with only some stubborn bits remaining.
Not hitting it hard, so far I have not damaged any stones.

I had been thinking about the belt sander option for the harder bits, might look into this. I don't fancy using chemicals if I can help it.

Thanks

Paul

 

[Flyfisher]

A 'scutch' tool might be useful.