Mortar a good way to soundproof round MDF window liners?

[ChrisKingston]

I've made some MDF liners to go around PVC window frames and have a gap of between one and two inches between liner and the bricks of the wall (there's a lip on the final layer of brickwork). I've built the liners around the frames so they shouldn't be too difficult to replace.

My main concern is noise from a fairly busy road. A surveyor suggested I fill the gap with mortar for soundproofing, but the plasterer said just use expanding foam.

Any ideas? I don't really mind from a time point of view and neither way is expensive. How about a couple of inches of mortar and then the rest in foam? Would that be the best of both worlds?

Thanks, Chris

 

[stevethespreader]

i think you will find that the sound proofing qualitys of mortar or render is next to zero