Victorian fireplace hearth - dig out structural cement or just replace cracked screed?

[Bill510]

Not a wizened DIYer so please forgive naivety and incorrect terminology.

I have a couple of fireplaces in my ground floor Victorian flat, both with approx. 2cm of old (cracked) screed over approx. 20cm of cement (lots of large stones in this lower mix). This all sits on a rubble filled, brick lined stack - which descends about 1m into the sub-floor. The front and sides of the top of the stack are lined with joists, in good condition.

The screed was heavily cracked at the sides of the hearth where the structural cement below did not reach the joists (below the screed here was just rubble, which I have pulled out). It's as if the cement was poured in but didn't reach the sides). I've since pulled up a bit more of the screed, as visible in the pictures.

I am not planning to use the fireplaces, just want to get them to a decorative state. Is it viable to remove all the screed, pour cement into the cement gaps abutting the joists (lining with plastic rubble bags) to the level of of the historic cement, then re-screed the whole thing? Or does the structural cement need replacing wholesale?

If I were planning to use the fireplaces would it be a different story?

I have full access to the sub-floor at the moment.

Any advice appreciated greatly! Pictures attached from one fireplace (joist position marked in red).

 

[JohnD]

the rubble and hearth have no DPM so are naturally damp. this can cause the chimneybreast and adjacent walls to be damp.

this did not matter much when a fire was lit every day to keep the hearth and chimney warm and fairly dry

if you are working on it, dig right down and take out all the damp rubble. you can knock out a couple of bricks enabling free ventilation to the subfloor void.

clean, unplastered, ventilated brickwork will only let damp rise up a couple of courses

You can make a new hearth slab with dwarf honeycomb walls and a couple of paving stones, or cast one.

If you will not have an open fire again you can let the subfloor void ventilate up the chimney if you want (the flue must also be open at the top so damp can escape) and you can put in a wooden floor instead of a slab.

If you want you can put in a hatch or a floor safe

 

[Bill510]

Apologies for the very delayed reply. Thank you very much for the reply @JohnD