I have a wall that I have soundproofed by adding a few layers of soft caulk (to create small air gaps), foam paneling, and extra layers of drywall. It is now fairly quiet. However, the bottom 1-2 inches were not made thicker because the wall is ~98" tall, I worked from the ceiling down, and I used 8' (96") plywood and foam sheets. I also don't want to put drywall in contact with the floor because of a) thermal expansion and b) possible spills.

Now most of the sound comes through the bottom of the wall which is 1) trim (on the other side), 2) small air gap under the drywall on the other side 3) 4" of a 2x4 that is the bottom of the framing and now 4) A few inches of air underneath my new thicker sound-proof wall.

What is the best material to use to fill this gap before I put the new trim on my side of the wall? I was thinking of small custom-made sand-bags? Or spray foam? Something else?

  • i would cut foam into strips and stuff them in the gap. The best to use would be dense/heavy latex, think dynamat w/o the expense. Cheap vinyl-coated flat pool rafts are usually dense and heavy. Maybe yoga/gym mats, garden pads, or workshop anti-fatigue mats would fit the bill as well. – dandavis May 16 at 20:24
  • Thermal expansion of drywall?? I can't even imaging that being an issue. – isherwood May 16 at 20:58
  • Thermal expansion of the floor (concrete w/ radiant) that drywall might be resting on. But mostly spills. I never see drywall in contact with the floor behind floor trim, and assume there is a reason for this... – mankoff May 16 at 21:35
  • Rock wool acoustic insulation would be one choice. – Ecnerwal May 17 at 3:25

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