Hollow Block walls, should i fill em with sand?

Hello my dear fellows So im back, and about to embark on another studio project, my Clients in Surrey were very happy with the studio i built for them there and having run it for them for abut 18 months now , im realsed from contract and time to move on, I plan to buy a commercial space in a basement and fit a 2 control room i live room 2 booth layout, and i was wondering about as im in the basement using hollow concrete blocks to build the walls out of, if i fill them with sand will the STC rating go up much then leaving them empty? i looked em up on the chart on here and they seem very effective hollow agaisnt Dry wall and stud for cost , but would a sand filling make em even more soundproof? cheers steve

adding sand will increase the mass of the block and you'll get an increase in STC but filling with concrete will give you more and painted with two coats either side will give you even more. i.e a plain hollow core block = 48 STC hollow core painted both sides = 53 STC hollow core sand filled and painted both sides = 56 STC hollow core, masonary filled and painted both sides = 60 STC. hollow core, masonary filled and plastered both sides = 63 STC.

HI john thank you for kind and detailed reply, im amazed at the improvement of just painting the blocks!! would you say its cheaper in time and materials cost to go block and concrete, over stud insulation and dry wall? i can see an advantage in less Green glue, less caulking and less chance of builders not getting the overlaps right and so forth. best steve

hollow blocks are very porous - they absorb water if used externally without a proper eave and not painted. The paint seals them airtight. I suspect with all the angular construction and lintels for windows etc a stud wall with a double layer of 16mm drywall )Greenglue not required) would be cheaper, and faster to build yet return a similar STC.