restoring slate flagstones

[stanleymanley]

We have a problem... we have uncovered a lovely old slate flagstone floor in our new house, the previous owners have filled in the joints with what appears to be a strong concrete mix inbetween and slightly over the joints of the flagstones. Our ultimate goal is to lift the Flags to insulate, damp proof and install underfloor heating. Could someone advise on how best to remove the concrete infill so we can lift the flags without damaging them

 

[Galena1]

Hi - How wide are these joints? I have cleaned joints out using a small angle grinder, fitted with a diamond disc, and a vacuum cleaner. The angle grinder is applied to the joint and the end of the vacuum hose is held close to the back of the disc to collect the dust. Do it a small bit at a time, too much and you'll create more dust than the vacuum can handle.
You will inevitably get some dust escape but this can be kept to a minimum with careful positioning of the end of the vacuum hose.
Only remove all of the joint from one slate. This should, with a bit of luck, enable it to be taken out. It depends on how/if they've been fixed down. With the rest, just cut right down through the joint. You can then take them outside to grind off the rest of the cement. Less messy than inside.
Make sure you wear safety glasses and a dustmask.
Also, get a plentiful supply of cleaner bags, they clog up with the fine dust from the cutting. The bags will clog up a long time before they are full.
Regards