Who do I need for this? A builder?

[LizTerrine]

The fireplace in the dining room was filled in by previous owners. The area where the hearth would be was filled with concrete. We've not touched it, except to have a specialist render over the top when we had the damp proof course in that room redone a year ago.

There now appears to be moisture leaching into the hearth/concrete from where the fireplace was. The plaster above is not damp - just the floor. It's spread out about five centimetres and has grown visibly larger in the last week.

I'm a bit baffled as it hasn't really been raining that much, and we've never seen it before. It's a party wall, so I guess worth going round to have a word with the neighbours. It's likely to be the chimney though, isn't it? :(.

Do I need a general builder, or someone more specialist?

50p says there is an old back-boiler pipe that is leaking.

Somebody needs to hack up the concrete to look.

A general builder can do it.

If not, you may need to dig out the old fireplace and find the DPC, and lay a new plastic DPM before refilling.

The old chimney must be ventilated to prevent condensation. If you are digging out the hearth you may be able to put in a duct so that air from under the floor goes up the chimney. This will prevent draughts in the room, and help ventilate the subfloor as well.