Back in the 1960s the former owners of the house I'm currently in decided to put concrete onto the 300 year-old, five-inch thick interior flagstones. It varies in depth and adhesion, from 5mm to 2mm. Some I can strike off using a mallet but much of it seems to be stuck fast. I can chisel it off but that is going to score the stone. Has anyone tackled this problem before? I've read that hydrochloric/muriatic acid can be used but I'm loathed to use this because of the environmental factors (e.g. what to do with the acid afterwards, etc.) Is there anyway I can remove this stuff?? :?
- Thread starter wolfpaw
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Hi Wolfpaw, welcome to the forum.
At 5mm to 2mm it isn't going to be concrete. I guess you mean cement but it is really too thin for that too. Is it some self leveling compound or similiar? A picture would be useful for comment too as it is best to work out what you are trying to remove before attacking it.
Anything acid is going to attack the limestone so you want to avoid using that.
At 5mm to 2mm it isn't going to be concrete. I guess you mean cement but it is really too thin for that too. Is it some self leveling compound or similiar? A picture would be useful for comment too as it is best to work out what you are trying to remove before attacking it.
Anything acid is going to attack the limestone so you want to avoid using that.
MdB said:
Thanks for the welcome
I'll take a photo tomorrow and post it on here. I have some of the flags lifted out at the moment as a waste pipe is being laid. If it's not concrete or cement then I've no idea what it can be. Parts of it lift away in large flakes while other parts are totally stuck. It's very dark in colour, almost black. Could it be a sort of glue? There was a carpet laid over the top of them when I moved in.
Edit: just been looking online and I'm wondering if it's something called 'thinset' mortar, a tile mortar made of cement and fine sand. Perhaps they laid tiles down at some point and used this stuff to stick them to the flagstones. :roll:
Anyway, will return tomorrow with a pic
benmc
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Is the black stuff sticky in any way?
I am wondering if it is Bitumen, used to stick something down before.
If so the heat will soften it or White Spirit will dissolve?
I am wondering if it is Bitumen, used to stick something down before.
If so the heat will soften it or White Spirit will dissolve?
essexbearhunter
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The small stone particles visible in the edge shot suggest some formulation of of cement (the stones being from the sand) rather than a levelling compound.
Perhaps the next question to ask is "What finish are you hoping for?" Unless there is a significant layer of oil/fat/wax on the flagstones (unlikely in view of the difficulty that you are having removing the top screed) then a "time-worn cathedral flagstone" smooth finish isn't going to be "liberated" however carefully you remove the coating. That is not to say that it cannot be created afterwards.
Unless you are lucky enough to rive/split the stone+concrete at the exact point of their meeting, you will inevitably remove a tiny layer of the stone - effectively recreating a new surface whether you want to or not. The use of some form of abrasive to remove isolated bits of cement would not be "out of order" unless it created deep scars. How deep the scars from this - and your actions to split the two layers apart - can go before they ruin the intended effect of the floor, depends on how you will be "processing" the revealed floor to create the finish that you want.
If you need to smooth (but not flatten) the surface to give a quietly undulating finish then extra sanding/scrubbing can mellow out areas that show evidence of your removal techniques.
Perhaps the next question to ask is "What finish are you hoping for?" Unless there is a significant layer of oil/fat/wax on the flagstones (unlikely in view of the difficulty that you are having removing the top screed) then a "time-worn cathedral flagstone" smooth finish isn't going to be "liberated" however carefully you remove the coating. That is not to say that it cannot be created afterwards.
Unless you are lucky enough to rive/split the stone+concrete at the exact point of their meeting, you will inevitably remove a tiny layer of the stone - effectively recreating a new surface whether you want to or not. The use of some form of abrasive to remove isolated bits of cement would not be "out of order" unless it created deep scars. How deep the scars from this - and your actions to split the two layers apart - can go before they ruin the intended effect of the floor, depends on how you will be "processing" the revealed floor to create the finish that you want.
If you need to smooth (but not flatten) the surface to give a quietly undulating finish then extra sanding/scrubbing can mellow out areas that show evidence of your removal techniques.
The bottom line for me is that they remain in the house. They have been here for 300 years and I don't want to be the one to ditch them. The amount of work that went into fashioning them was immense. They are in a 10'x15' entrance hall. I do have some replacements that I found a long time ago under a shrub and which must've been removed from the house before the cement-type stuff was added. Maybe I can reuse those. I'm tempted to take them all up anyway as they are currently on a bed of clay and I would like to add a scree bed for them to rest on. I could see how many I can salvage that are cement-free and then see what I can do with the others. It just irritates me that they have been damaged by some bumbling bodger who wanted to 'modernise' in the 1960s
essexbearhunter said:
Penners
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Judging from your picture, that looks very much like some form of concrete - there appears to be a gravel aggregate within it.
Have you considered turning the slabs over? If you're going to be lifting them anyway, have a look at the underside. If it's smooth, then the easiest route might simply be to flip them all, relay them and give them a good clean.
Have you considered turning the slabs over? If you're going to be lifting them anyway, have a look at the underside. If it's smooth, then the easiest route might simply be to flip them all, relay them and give them a good clean.
Are you talking about brick acid? Check the last review here <10% concentration of Hydrocloric acid.wolfpaw said:Unfortunately the undersides are very uneven
So is the hydrochloric option out of the question? :shock:
We used a bit on some of our floor bricks that were really badly stained with cement. I wasn't massively impressed with it's effectiveness above giving a thorough clean. You could try a test but I wouldn't bet much on it working well enough to remove that stuff.
I appreciate you're commitment to the floor having spent a lot of time salvaging mine, it's a labour of love. You might want to check out your local granite suppliers, monumental masons etc. They may be able to advise on how to remove the cement stuff or offer a suggestion about refinishing the undersides of the flags. The guys who installed my kitchen work tops told me they would have been able to cut my floor bricks more quickly, cheaply and effectively than we managed with a masonry bench saw we hired.
Penners
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What are the slabs? Are they limestone?wolfpaw said:
If so, then any acid would be a risky proposition.
Acid = acid. Limestone = alkali.
Combine the two and you can get a pretty violent reaction.
AMc's experience is on floor bricks, which are clay. That's rather a different proposition. His acid was also quite a weak concentration.
Maybe you should try some hydrochloric acid (a weak concentration initially - maybe 10%) on a small test piece - perhaps the underside - of one of the slabs. Just see what happens. If the stone appears relatively unaffected, then try a test on some of the concrete skim.
Carol
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Looks just like the self levelling compound liberally spread over our flags in the seventies -the barbarians! We had success levering off large chunks with initially anything that came to hand, including fingernails and some was carefully chiselled away. Some was removed with HG stuff (chemical, but can't remember what) designated for flags, but some is still in situ but not noticable as it has weathered/dirtied to similar colour to the flags! (It's not a pristine house!) We have found the last bits have begun to disintegrate with footfall so perhaps this is a possibility.
Good luck with attacking yours, it is well worth it in the end.
Good luck with attacking yours, it is well worth it in the end.
Penners
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Well, I suppose it could be, but personally I've never come across a levelling compound with gravel aggregate in it, and those photos do appear to show this.Carol said:
There was a levelling compound on top of the tougher layer. I managed to chisel the levelling compound off using a mallet and chisel. I've been trying again today. I just don't know what to do really. I've worked out that I don't have enough spare flags to replace the ones very heavily coated in this cement-like stuff. I'm going off the chemical option as I can't see it eating through up to 5mm of the cement. This leaves two options: remove the slabs and replace them with a cheap modern imitation (I can't afford to replace them with ancient ones) or try and chisel off the cement by hand, millimetre by millimetre, inevitably damaging the surface of the stone in the process. I think what I'll try next is to use one of them as a test piece and see how badly damaged the surface gets by taking if off by hand. I don't see any other options at the moment.
The fact it was done at all though makes me good and mad! :x
The fact it was done at all though makes me good and mad! :x
Carol
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I couldn't see gravel! Just sheets of nasty grey stuff.
Sounds a little like the weathering of kimberlite (the mineral substrate that diamonds are found in in South Africa) that on the surface is yellow and soft/easy to work "yellow ground" where it has been oxidised/weathered but at depth is unaltered "blue ground" that in the 1870s was too hard to work and made claims almost worthless until lumps of it that had been blasted out at huge expense with newly discovered dynamite and then abandoned on the surface started to breakdown over time and reveal diamonds.
I guess that was a very roundabout way to encourage you to continue at it and the diamond in the rough will out eventually!
MdB said:
:lol:
If I do proceed with the 'chipping it off with a chisel' approach does anyone have some suggestions on how I can eliminate the inevitable scratches to the flagstone surface? What sort of sanding, etc. should I use to remove them? As another poster said, I too am not interested in getting a perfect finish as it's an entrance hall in an old farmhouse. I don't want it looking like it's been hacked around though. :?
JoceAndChris
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For finishing your flagstones and eliminating scratches, you could try fine wire wool soaked in soapy water and rubbing away over the course of a day or two. There are different sealers and floor waxes you can buy that would fill in scratches, for example the Liberon system. (which I haven't used yet, but plan to)
http://www.liberon.co.uk/flooring/stone,434,464.html?&args=Y29tcF9pZD0zMDQmYWN0aW9uPWxpc3RlUHJvZHVpdHMmaWQ9NDAmfA%3D%3D
Good luck, it sounds like a horrible job. Can I ask about the shape of the flagstones - are they all the same shape or have they been cut differently to fit peculiar little spaces? (I wouldn't be able to rearrange flagstones here as they've been laid for that specific spot) Just wondering if you could lift the lot, get the cement off, and put the attractive ones round the edge with a nice rug in the middle. As Penners said, there might be one or two that look better flipped over, even if they are uneven.
http://www.liberon.co.uk/flooring/stone,434,464.html?&args=Y29tcF9pZD0zMDQmYWN0aW9uPWxpc3RlUHJvZHVpdHMmaWQ9NDAmfA%3D%3D
Good luck, it sounds like a horrible job. Can I ask about the shape of the flagstones - are they all the same shape or have they been cut differently to fit peculiar little spaces? (I wouldn't be able to rearrange flagstones here as they've been laid for that specific spot) Just wondering if you could lift the lot, get the cement off, and put the attractive ones round the edge with a nice rug in the middle. As Penners said, there might be one or two that look better flipped over, even if they are uneven.