Has Anyone Actually Used Hydrochloric Acid to Clean Flagstones? (and other queries...)

[Rich1972]

I've seen it posited as a possible solution for removing cement from flagstones but has anyone actually tried it? Is it possible to do it with the flagstones in situ?

I have a flagstone problem in that I don't have a complete floor of them. The kitchen area has about one third remaining original 18th century flagstones that had been covered up with a thin layer of cement/concrete and/or a plaster-like finish to make the floor level. [:'(] The rest of the floor is concrete, with a foot-wide channel hacked through some of the stones when they put a water main into the house [:(] I really want to keep the few flags that remain, about twenty in number, and which measure about 2.5ft by 18 inches. They're part of the house and part of its history and are wonderfully worn in places. I can't afford to take the floor and up and replace the entire area with reclaimed stones, incorporating the ones I've already got, but I don't want to ditch mine either.

So I want to clean them up as best I can but I'm not sure I can use hydrochloric acid with them still on the floor (the stones are resting on stone pillars, creating about a 12-inch void underneath before coming down onto the bare earth). I've thought about taking the concrete up and having a DPC put it.

Do people who move into stone houses automatically put Damp Proof Courses under the floors? I've read conflicting reports about them e.g. they can push damp up into the walls but they also provide decent insulation, etc. etc. I'm coming to the conclusion that allowing the house to breath through the walls and floor is part and parcel of living in a stone house, in which case DPCs aren't necessarily a good idea. If I did take the existing flagstones up then how would I do it without breaking them (or breaking my back!). Has anyone restored an original (partial) flagstone floor?

Any views welcome

Rich [:)]

[Alan Zoff]

I tried the hydrochloric (muriatic) acid on some old thick floor tiles and it was no help at all with the removal of cement/concrete stuck to the bottom of the tiles. (I had lifted them all and was hoping to re-use them.)

It fizzes (and takes off the pattern if spilt on the painted surface of the tiles) but removes only the tiniest bit of cement. It would take gallons of the stuff to clean all the tiles - but I wonder if the tiles were made from a similar concrete to the stuff used to bed them down that I am trying to remove and they have almost become one.

[TroisChatNoir]

have you tried very gentle pressure against the affected areas with a coarse grinding disc on a small 115mm grinder? I use this method on stone work or stone flags that have been stained by cement based products with good results but be gentle! you could then polish off with a floor polish to buff them up if required. try & lift them with a big crowbar after cutting out the mortar joint all around they should be laid on a sand/lime mix which will lift up with them, this should be taken off before relaying, your floor sounds as if its been built on the pillars to allow airflow

and stop the capillary action of dampness coming up through the soil

into the floor a bit like honeycomb walls for floor joists before the

onset of concrete foundations and DPM arrived

I never put a damp course into stone buildings unless its a new cavity construction, older houses were built in different ways to combat dampness using  air gaps & impermeable or robust materials where necessary, sealing them off with DPC's & double glazing then installing central heating radiators etc doesn't allow the natural products to "breathe" and often creates more problems than it solves, better to use a wood burning stove/range somewhere in the house to draw the moisture out of the walls and out through the chimney than to try & stop it happening in the first place.

you are quite right stone houses have character and are a joy to live in as long as they are treated for what they are.

 

[Rich1972]

Interesting replies, thanks!

I think the acid idea will go on the back burner for a bit until I've tried other options, including the grinding disc. The flags aren't totally covered in 'black concrete', although some are worse than others. The house seems to have all sorts of floor surfaces. Concrete is in all rooms to some extent or another. The raised flagstones are in the kitchen and the sitting room just has one-inch deep irregular flagstones over most of it, resting directly on the bare earth. This is the room that concerns me the most, even though these stones would be much easier to lift than the large ones in the kitchen. All the old linoleum I've taken up was damp to the touch underneath, which just proves that the plastic was preventing the humidity from evaporating. Either way, I won't be dealing with the floors until next year. I think only by living in the house for six months will I get a good idea about what needs doing, especially after I've had the roof and chimney stacks done (which leak), and replace the badly cracked lime rendering on the outside walls. When I moved in last month the house had been empty for six weeks and the smell of damp was very apparent. But with me here now, using the house every day, it seems to have got a lot better. I really don't want to lift the concrete floors unless it's absolutely necessary but reinstating the remaining original flagstones is a must.

[BIG MAC]

Is lifting them and having them sandblasted an option?

[Postie]

I don't think there's easy solution. It might be possible to carefully lift flags & turn them over. You'll loose your "well worn" look but will probably get a "cement free"  surface on the other side. We do this quite often when restoring furniture.

Postie