Water under suspected floor and rotten joists

[NewbieOnHolidays]

We recently bought a 1930s house that had a fair bit of black mould around all windows plus during renovation we discovered that the corner behind kitchen cupboards was covered completely in black mould, joists under the kitchen were rotten and there was some water collecting under the suspended floor on concrete. We had multiple specialists coming to have a look, all offering different treatments (whatever they were specialists in they would try to sell it to us as the right solution). So we replaced the main water supply pipe with a new one, put new joists in, had cctv inspection of drainage, fixed gutters. Issue still seems to be there as when I open cupboards of our new kitchen it smells of damp and I’m worried mould will soon grow on new joist s and new kitchen. we had yet another specialist coming in and saying we need a new DPC with injections into the voids between wall and plaster, they said plaster was put on top of old DPC and water collecting between plaster and DPC. Quoted us for £1500. I wonder what if it doesn’t solve the issue. What else might be causing the dampness?

Have you had a drain survey? Old cracked drains can cause problems.
Sedited - sorry didn't spot that you have already done this.

Did you strip the damp bits right back to brick before you put the kitchen in?
Where is the damp proof course? Is it above where the concrete is on the internal floor? Are there any pipes near the damp bits which could be leaking?

If you can smell damp then it sounds like the problem hasn't been completely fixed and will need some extra work.

Was there actually a leak in the main water supply pipe?

We are not sure, but the old one was very old, lead type and we were told getting a new bigger one would improve water pressure

What are the exterior walls like, is water coming in from leaking gutters or something? Has the property just not had time to dry out?

I wouldn’t spend on any treatments until I was 100% sure I knew where the water was coming from.

We are not even sure if there is a damp proof there, but the last person to be here said that it’s there just that the rendering was put above it and water collects in the void between dpc and render.

the pipes were all fixed as far as we can tell

How deep is the void between the wooden floor and the concrete slab? Do you have enough air bricks and they clear and working?
A 1930’s house will have a DPC.
A couple of pictures of the exterior brickwork would help the hive mind. I would guess that a damp/wet problem as you’ve explained would take a year to properly dry out.

Adding a few photos

One more

And another

My bet would be on the render being blown and letting water in. None of the damp "experts" would have suggested this because, as you say, they all decide the problem is the one they can "fix"....there is a book called The Warm Dry Home by Peter Ward, would be worth a read before you invest any more money

Those airbricks do not look that clear. Did you identify if the dpc is about level with the top of the blacked render or the top of the airbrick? If I top of the airbrick, then your ground level is too high. Anyway, they are talking rubbish about the injections, they won’t help. Where the render has been knocked off on the corner, that looks pretty good brickwork.
I’d say you need to investigate that the drain is working correctly and that stack pipe also is not cracked below ground. If it was me, I’d get those slabs removed along that wall and expose pipe work by digging it out a bit. Does not need to be a wide trench. All being well, but I suspect you’ll find an issue, you can backfill the trench with stones/pebbles so any water drains down.