What fixings on these hollow bricks?

[Astronaut_elvis]

We've undertaken a DIY project to soundproof an upstairs bedroom party wall shared with our noisy neighbours. There's a window on the perpendicular wall so there's only approx 70mm before the party wall would hit the windowsill which limited options.

We decided on resilience bars, sbx boards (boards filled with sand) and a final layer of acoustic plasterboard (total depth 43mm). Unfortunately hit a problem when trying to attach the resilience bars to what we assumed was an aerated block wall but turns out to be some flimsy hollow blocks. Have been told by a friend they are 'pots' but not sure of the proper name. I can't find any further info from googling.
This is a picture of them in the loft and a close up of the middle of one of them where the hollowness can be seen.


The fixings for the bars are 6 x 60mm hammer screws but although it feels pretty solid I don't think I trust it has enough of a hold. The total weight of the sbx and plasterboard will be 30kg/m2.

I thought perhaps some kind of toggle or expanding fixing could work. As long as the blocks can even hold the weight.
Either that or a stud wall attached to the side walls/floor/ceiling but due to the lack of space it would have to be the slimmest wall possible while still supporting the weight.

Any suggestions on what the blocks could be? And the type of fixings that could be used? Or how the thinnest stud wall could be built?

 

[noseall]

European clay pots. Eeeeugh!
Fix into the bed joints.

 

[Astronaut_elvis]

European clay pots. Eeeeugh!
Fix into the bed joints.

Can’t see the joints in the bedroom where we’re fixing unfortunately unless we take all the plaster off.

If we were going to take all the old plaster off then would have gone for a glued system instead of fixings.

 

[tony1851]

Extruded clay blocks - hard and brittle.

Is it possible to cut 50mm wide vertical chases in the plasterwork (marking the lines with an angle grinder) at - say - 500 spacings so that you can see the mortar joints, and then screw vertical 50 x 50 battens to the joints. Then fix your resilient bars horizontally to those?

(Though might be difficult if they use a cement-based plaster?).

 

[robinbanks]

all the plaster off.

Pots will be a consistent enough size that you could measure from one bed you did find already?

Also, the difference in drilling clay vs mortar should be quite apparent..

 

[cdbe]

I would fix something like 200mm x 200mm squares of 18mm ply directly to the wall (remove the plaster) with a good quality "no nails" adhesive at each fixing point. I've just had a quick Google and one of the more expensive ones claims to hold 350kg/m. It's no wonder there is sound transmission if the party wall is built from them.