Resilient Bar Ceiling Airtightness

[MortarThePoint]

I'm trying to understand resilient bar installation. For it to have any acoustic benefit, it is essential to avoid short circuits like a screw going through the plasterboard, resilient bar and into the joist above. It's all about isolating the mass of the ceiling from the joist.

 

 

"Where Resilient Bar is being used for ceilings the bars are fixed at right angles to the underside of the joists as close to the perimeter of the room as possible without touching the walls" (link)

 

In the video below they use a silicone type sealant at the board edges, but it doesn't look very convincing from an airtightness perspective. I will have areas above the ceiling near walls that are exterior vented. I have some questions that anyone who has considered this before will likely have worked out:

1. Airtightness: How best to airtight the ceiling at its edges with the wall? This could be done at joist level, so maybe I need a membrane above the resilient bars.
2. Wet plaster: Can we just wet plaster into the ceiling corner and is short circuiting the ceiling to the wall is less of an issue?
3. Plaster cracking: Will the plaster crack at ceiling corners as it is possible the ceiling may shift relative to the walls slightly?

 

 

[Mr Punter]

Why does this ceiling need to be airtight?

 

For sound attenuation, the walls will make no difference.  It is the sound vibrations from the floor above that you are trying to minimise.  You also need to avoid flanking sound through gaps between the ceiling and the wall, which is what the mastic and plaster will do.

[MortarThePoint]

1 minute ago, Mr Punter said:

Why does this ceiling need to be airtight?

 

58 minutes ago, MortarThePoint said:

I will have areas above the ceiling near walls that are exterior vented.

 

Even with the top alternative insulation below, it may be difficult to get the space below airtight if not achieved by the ceiling.

[Mr Punter]

It is sometimes a good exercise to draw in where the airtight layer will be, then consider how it will work at all the junctions.

 

Your airtight layer could be polythene or plaster but it really needs to be contiguous.

 

The first option looks easier to achieve for insulation and airtightness.  The bottom one looks pretty flaky.