What would you plaster these internal blockwork walls with?

The walls divide off from the main living area the downstairs toilet & shower (wetroom), as well as another room which is the Utility/plant room housing GSHP & Hot water Tank, MVHR unit, washing machine, UFH manifold, and a utility room sink.

We have built them in block to add some more thermal mass inside the insulation layer, thought it would be better for the shower cubicle/wetroom tiling, better for fixing some of the kit/pipework in the utility, and to provide a bit of added support to the staircase.

Transmission of noise is probably the main consideration (but I don't want go to the lengths of resilient bars).

These internal blockwork walls could be plaster-boarded and skimmed, or sand & cement plastered, or any other suggestions? I could also do a different finish on each side, e.g. wet plaster inside the shower room, P/B on the hallway and stairwell face.

The external walls of the barn are all IWI insulated with 100mm PIR and so will be plaster-boarded and skimmed, so if we were to P/B these as well all the skimming could be done at the same time.
I'm not sure if soundproof plasterboard would help much in this situation?

Any thoughts?

I guess the noise you would be most concerned with is that generated at night. MVHR are quiet certainly mine is except when on boost so basically leaves the HP could that be soundproofed on its own?. Seeing the electrics is surfaced mounted I would plasterboard over as if you wet plaster the walls the skim coat over the trunking the plaster will be thin will show through or crack. My plant room is next to a bedroom a kitchen on the GF and en-suite and part bedroom over. It houses boiler MVHR manifolds TS etc and we are not disturbed by noise but we have resilient bars for the ceilings and any timber stud dividing walls. You may be over concerning yourself as DJH says you have some deadening mass. Make sure if you mount anything that can generate noise on a wall, you put on anti vibration pads/fixings/isolation to avoid transmission.

Thanks for the tips. I could do resilient bars on the ceiling of the utility.

I could go wet plaster on the inside of the shower cubicle /wet room (better for tiling?) and also wet plaster the inside of the utility (better for fixing pipes & cables?)

Then plaster board on the hall face and the stairwell face to keep the sound transmission down.

I wouldn't plaster the outside, internally, wet plaster c&s and skim

Just for clarity the hall is on the left in the picture, the first doorway in the blockwork is the shower and W.C., the second doorway is the utility, the opening at the end of the hallway goes through to the single storey kitchen at the end.
The stairwell is on the right (with the stairs drawn on the blockwork in pencil), the lounge is behind me / to the right with the open staircase in it.

Posted By: jfbhave you got a sound attenuator on at least the supply side of the MVHR?

yes flexible silencers and rubber duct couplings.

Posted By: revorif you mount anything that can generate noise on a wall, you put on anti vibration pads/fixings/isolation to avoid transmission.

I think this is a very important point, thank you.