Sandstone fireplace turning to dust - ideas welcome!

[Jay]

Hi again lovely period property people!

Seeking ideas for fixing an issue I thought I had already fixed

Background house info in case helpful: West Somerset 17th century sandstone rubble cottage

I have a huge beautiful inglenook in the living room. When I got the house I noticed some of the stones in the fireplace were rotting completely into dust, there was just a huge pile of dust on the hearth in the back corner.

The fireplace had essentially been slapped all over with cement trying to masquerade as actual pointing, so I had all that taken off, repointed in lime, and repaired areas where stones had rotted out too much to be salvageable.

The areas where stones had been replaced are now fine, but some of the older stone (I think it's called the quoins?) is still turning itself back into sand, so the lime obviously hasn't fixed it.

I have no idea what is causing the issue. What would have been the fireplace recess on this side of the chimney belongs to next door, and they just use it as a cupboard.

I know for sure there's nothing but plaster on the other side of these stones, because my builder popped an endoscope through what we thought was a bread oven at the time and it ended up going through plaster and giving him a great view of their iron!

As per the title, please feel free to throw any ideas at me as I am pretty stumped on this one.

Thanks in advance as always!

 

[Cubist]

At the root the problem is caused by damp which can also induce salts trapped in the stone to crystallise. The cement mortar repairs in the past won't have helped either. I've never faced the problem myself but Indian Sandstone Sealant is often used to combat the effects. Hopefully others here can offer a better alternative or confirm the efficacy of the above. Good luck.

 

[Itchinfilth]

I was in the same situation with fragile sandstone mullions which were shedding a concerning level of sand following the removal of cement and concrete. I used the product Beeck Fixative Silicate. Dilute it with water as p/ instructions and simply brush on. I think I gave mine around 15 coats. Not a grain of sand has come off them since. I was genuinely amazed at how successful it was.