Filling in Studio Walls

My Tracking room is as follows: Back Wall: 6"-7" airspace between sheet rock and concrete Control Room to Tracking Room Wall: 11-1/2" airspace between sheet rock Wall with Doors: 8" airspace between sheet rock The Back Wall I used Thermafiber 4" Thick 4psf. This left about 2-3" airspace between the Thermafiber and concrete. Control Room to Tracking Room wall I used Thermafiber 4" Thick 4psf on the Tracking Room side leaving 7-1/2" airspace. I plan on filling in the leftover 7-1/2" airspace with fiberglass and Thermafiber 2.5psf. Wall with Doors I used Thermafiber 4" thick 4psf. I plan on filling in the leftover 4" airspace with fiberglass. My question is should I not use the 4psf at all or is it ok since I am not touching the outside walls with it?

i'm unclear about what you are asking. is the thermafiber inside the cavity of the wall or inside the room as room treatment? and its hard to to picture what you are describing. have an image? do you use sketchup? from what i understand (and what i'm practicing) there is no point in using thermafiber inside a wall when the regular pink stuff works just fine and is cheaper. but if you are doing room treatments that's a diff story.

ah, saw your topic again. filling walls. ooops. yeah, just go with the pink stuff and insulate each leaf as you would a home.

So are you saying just add pink stuff or remove everything and replace with pink stuff? I'm more concerned with pink stuff against my concrete wall side. Even though it won't be touching, I have thoroughly covered the concrete with DryLock and I have a dry basement, I wanted to use mineral wool because of possible dampest.

i think mineral wool and fiberglass are both mold resistant. but honestly i'd make sure the waterproofing was sound first. mold or no mold excessive water/moisture is bad. a good product for "waterproofing" is xypex concentrate. i've used it twice with success. is this the drylock paint you are using? from what i know that stuff isn't nearly as effective. then again xypex is more difficult to apply. maybe you should wait for rain season before you close up the wall. serious. but i don't really understand what the concern is fiberglass or rockwool in a wall. what do you expect to gain from thermafiber?

cporro, Thanks for your input. I think you misunderstood my concern with my concrete wall. My basement is very dry compared to most homes where I live here on Long Island. I have only gotten a little water in my basement on a very rainy day only on the other side which is nowhere near my build. I have corrected the problem and after some very rainy days I have had absolutely no water at all. I have lived in my house for almost 10 years. My first year we had a small mold problem. This was due to hot humid summer months, unpacked boxes against one of the concrete walls and our dehumidifier not working. I now use 2 dehumidifiers and haven't had a mold problem in the last 9 years now. As far as fiberglass goes, take a look at this website... http://www.inspect-ny.com/sickhouse/FiberglassMold.htm I am no expert when it comes to what is better, but from my years working on houses anytime water got in contact with fiberglass it was never pretty ripping that crap out and replacing because it turned black and moldy. Whether mineral wool is a better choice, I couldn't say but I have read that it doesn't get soggy like fiberglass when exposed to water(unless you add soap). I don't plan on having a problem with mold or moisture but it is a basement and if water gets in your house somehow, thats where its going. My other concern was I didn't want the fiberglass to touch the concrete like most have advised on the forum and by using mineral wool it made it easier since its more rigid and stands straight. I have put it up on the concrete wall side of my studio(see above). Just would like to know since its 4psf and not touching the concrete am I losing isolation since its 4psf and not 2.5psf?

i think the difference between 2.5pcf and 4pcf in a wall cavity is going to be negligible. if you were using them as room treatments...well, there would be a difference in absorbtion but nothing huge to my knowledge. even if you leave the insulation out of the wall you aren't going to see dramatic changes in the STC ratings. i have a standard wall (2x4 framing, 2 sides of 5/8th" drywall) at an STC of 33 and one with insulation at 36. if you fill something with like 9" of insulation you will start to see a greater (maybe 10-14) reduction. personally i would not sweat what was in the wall, just put something in there.