My first forum question (DIY) - hardwall on bonding?

[Af001]

Hi, got a question. I’m soundproofing a brick firewall in the loft. I did half in
Bonding before I realised hardwall is probably better. I need to put another coat on before multi finish, but run out of bonding - can I put a coat of hardwall on top of bonding, if I PVA first ? Or could I mix hardwall with MF as a first coat to flatten out, with a skim on top?

 

[S a plastering]

Soundcoat

 

[S a plastering]

Then independent metal frame 50mm acoustic insulation then 2 layers of 12mm soundboard then skim

 

[Af001]

Hi, thanks for the reply. Building control suggested it only needs 2x coats of render, not looking for full soundproofing, as the rest of the party wall in the house is just 9” brick with lime plaster. I also don’t have much room to play with as I have a staircase going in and if the wall comes out more than 30mm then it’ll kick the stairs out. I tried finding sound coat and struggled. Have already put a coat on - see attached photo - one half of a partition wall with bonding (left) and the other with hardwall. It’s the bonding that needs another. You can see there are still peaks where the brickwork from the wall (all over the place) is sticking out and low points where it still needs building up and levelling - in some places needs about 8mm which I’m guessing is too much for MF?

I’ve scratched it and plan to PVA before the next coat. What if I put hardwall on and then MF just as it’s going off??

otherwise I’ll need to wait until I can get hold of 1/4 bag of bonding.