Cleaning Fireplace Stone

[Superduner]

I'm lucky enough to live in a 400 year old stone house in France.
When we moved in 5 years ago we installed a woodburner into an existing fireplace/inglenook which was covered with many, many years of burned on soot. This summer's main project is to clean up the stone.
I've tried woodburner glass cleaner which takes off a lot of the worst of it onto a paper towel (but is very expensive on paper towels), and
Amazon will deliver today a foaming product that is supposed to be good, but has the potential to be a very expensive solution. The stone is mainly limestone, but there are a few more absorbent ones dotted about - maybe sandstone.
I had a go with a small hand held steam wand, which also helped a bit, but was wondering if anyone on the site had a quicker and/or easier way of doing it.
I really don't want to go through the hassle of clearing the whole room in order to needle gun or grit blast. We have pets, so strong chemicals like TSP are probably not a good idea either.
It's not realistic to expect cleaning to the original colour, but I'd like to get the stones as light as possible.

 

[Jacob]

Industrial paint stripper might do it. The gel variety which you can leave on for 10 minutes or so. Paramose or Langlows and others. They are supposed to be restricted to the trade but seem easy to get hold of.

 

[Fitzroy]

Most of the stone cleaning (granite) in Aberdeen is done with a strong acid to actually breakdown the top layer of the stone which takes the dirt with it, the stone comes up gleaming afterwards, it can actually be too aggressive and look too new. Not particularly helpful but that's what the granite city has found it needs to get rid of all the years of blackening, which I assume is mostly soot of one sort or another.

 

[Geoff_S]

We’ve got modern limestone fire surrounds and we were told not to use any sort of acidic cleaner. If we wanted to give them a clean from time to time we were told to use wet and dry sand paper with preferably water only although a mild soap solution could be used with care. Sandstone is very porous apparently so if it gets stained, it’s stained!

20+ years on, they still look just fine. Another 380 years, who knows?

PS how about some pics?

 

[MARK.B.]

Be careful with porous surfaces like sandstone covered in soot as liquid cleaners could just cause the soot to seep even deeper into the surface rather than removing it

 

[mikej460]

You shouldn't use acid based stuff on calciferous stone like limestone, marble etc. I would bet the only solution is mechanical removal. We had ingrained soot on our brick inglenook and the only method we found to work was sandblasting but it did take off the surface layer of the bricks. If I had to do it again I would try soda blasting or similar.

 

[woodieallen]

Mechanical removal. The stone is porous. Think wood. Would you add a thinner to try and remove a stain or something on the surface?

 

[Lorenzl]

You could use dry blasting - no longer sand - a video I was watching the other day was using baking soda as it isn't as rough and the pressure turned down.

Another product is CO2 and you don't have the problem of cleaning up so much. Similar to dry blasting but uses CO2 liquid which comes out as "ice" and "explodes" when it hits a warm surface.

 

[Fitzroy]

No idea if they can be hired but those new laser zapper things

 

[Superduner]

Firstly, thanks for all the replies to my post.
As requested, here are a couple of pictures of the fireplace back wall.
On "Fireplace 1", the left hand side was outside the fire zone. The middle, brownish bit has been given a once over with woodburner glass cleaner (but was like the right hand zone), and the black zone on the right speaks for itself. A closeup of the soot zone is in "Fireplace 2"
I'm going to get it all more or less soot free, and then maybe give it a quick dab of acid.
The Amazon cleaner, btw, was no better than the glass cleaner, but 4 or 5 times more expensive.

 

[Superduner]

And for anybody who is interested, the after picture.
5 rolls of kitchen paper, 4 bottles of bbq cleaner, a couple of wire brushes, a sponge, plenty of water, and 3 days of being bent over under the mantlepiece.
Not perfect, but as good as it's going to get without serious cost and mess.
You can just see behind the fire a piece of foil covered chipboard which hopefully will reflect some of the heat back and up to be blown into the room by the 2 heat powered fans on the flue.

 

[Fitzroy]

Great job, must be tired now! Looks splendid.

 

[Superduner]

It's very clear to see that the acidic soot has eaten into the stone in places (quite a lot of places), but overall the foaming bbq cleaner seemed to draw out the discoloration very well. If I went over it all again, I might be able to get it a shade or 2 lighter, but life is too short and my next project (replacing wooden terrace railing with a tensioned cable system) beckons.
If I don't keep busy on the more technical stuff around the place, I get relegated to lawn mowing duties!