Finding a sound insulation flaw in a party cavity wall

[nobodynevercares]

We've moved into a new flat almost a year ago. Eventually we found that our bedroom party wall does not meet the 45dB requirement.

The wall is a 75 mm cavity wall made of 100mm aircrete blocks with pargecoat and plasterboard on dabs. We can hear our neighbors speaking or watching TV. The sound test says the wall only reaches 43dB.

We've been fighting with the builders for more than half a year now and they still can't tell what the problem really is. I've set up a mini page with lots of pictures of the wall with comments and also documents such as sound test report, regulations, blocks used and suggested remedial works.

http://www.kokybiski-baldai.lt/party_wall/index.html

I feel that the builders just try to experiment with random solutions without really knowing where the problem is.

I have questions which I can't answer myself as I'm a software engineer by profession :/ but I hope you would:

1) Is there anything obvious you can see that is wrong with the wall?
2) How should a concrete block be isolated within a cavity wall?
3) Can a party cavity wall stand stand on a continuous concrete slab as it seems regulation says it cannot.
4) How should the wall be connected to the ceiling and floor. I've heard something about flexible/soft joints.
5) The regulation says wall type 2.4 needs to have a step or stagger. What does it really mean so that a simpleton like me could understand?
6) Can plasterboard from the ceiling or adjacent walls touch the wall or should there be a gap?
7) Is it possible to nicely cover all the drilled holes in the wall used to inspect the cavity without obstructing the cavity itself? Will it affect sound insulation?
8) Should the parge coat be spread very evenly and nicely?
9) Is it really bad that the parge coat is only 2 - 4mm thick when the recommended minimum is 8mm?
10) Would the recommended solution help? In short it is to cover everything in more parge coat, fix the gaps with mineral wool, sealant and parge coat. And hang a sound blocking plasterboard on sound resistant steel studs.

Thank you for any answers or tips,

 

[Deluks]

10) yes. But I wouldn't worry about the large coat.

 

[joe-90]

The best tip is to stop listening to it - you'll never sort it. We've never in the history of the forum had anyone come back and say they've sorted it.

I live in a house that is next to - but not connected to a neighbour. He has a 9 inch brick wall - then a 4 inch air gap then I have a 9 inch brick wall - but I can still hear them walking about. It's all to do with sympathetic resonance between similar bodies.

You'll never sort it. Learn to live with it.