How does Green glue work you ask? I'm glad you asked. Green Glue is a product designed to dampen 2 wallboards (such as Drywall or MDF or OSB) when it is sandwiched between these 2 rigid surfaces. Now buy damping the walls ceilings or floors, you are actually removing the resonant frequency characteristics from the wallboard itself. In other words the drywall for instance will not be able to vibrate with the passing sound and will hence be incapable of passing the sound. Lead and Mass Loaded vinyl and even manufactured soundproof drywalls like Quiet Rock or Supress still can readily pass certain frequencies thus allowing the noise to pass, not all noise, but certain frequencies. Green Glue on the other hand damps the wallboard (drywall) and thus stops all frequencies even the low under 80 Hz frequencies. This is precisely why Green Glue is the latest revolution in soundproofing, but enough of that, lets talk about soundproof floors and Green Glue.
If you are soundproofing a floor above from the neighbors below, you have many options to choose from however for the sake of time we will talk specifically about the Green Glue Method of soundproofing.
Your first order of business is to sweep and completely clean the bare sub floor. For this application we will be talking about a ' plywood sub floor, but the Green Glue method can be used with Gypcrete or solid concrete floors. The next step is to cordon off 4' X 8' areas where the Green Glue will be applied. In other words, using a chalk line, you will snap lines that are 4' X 8' (which are the dimensions of drywall, MDF and OSB) You will need to do the entire floor this way. Then you will take the tubes of Green Glue and load them into a quart size caulk gun and will then apply the Green Glue in a 'S' or figure '8' pattern until the entire 4'x 8' area is covered with the Green Glue. You do NOT trowel or smother out the Green glue, you simply apply a layer of OSB (oriented Strand Board) atop of the Green Glue and screw the OSB down as tightly as possible, always use screws not nails for this installation.
Now once you have the entire floor layered with the OSB and Green Glue sandwich you come to a crossroads. If you need to build up the floor to a certain height then you would repeat the process over top of the previous layer of Green Glue and OSB. If you choose this method and will be using multiple layers of OSB and Green Glue then 2 tubes of Green Glue per each 4'x8' sheet of OSB will be fine, however, if you are only using 1 layer of 7/16' or 5/8' OSB then it is highly recommended that you use 3 tubes of Green Glue per 4' X 8' area.
Once you have completed this phase of the soundproofing, you are ready to lay down your finished floor. This finished floor can be engineered hardwood, Carpet and Padding or even ceramic tiles. It doesn't matter with the Green Glue method what finished floor you install, the soundproofing has already be accomplished at the sub floor using the Green Glue. A little hint, Green Glue is a great sealer as well however it should never be a replacement for Acoustical Caulking. When you purchase your Green Glue for the floors, always remember to order 2 or more tubes of the acoustical caulk to seal heating and HVAC duct registers, light switches and electrical outlets.
The Green Glue application can reduce the Impact noise by up to 60% and it can reduce the airborne sound by as much as 75%. I hope this has helped you in your quest for the best and most effective floor soundproofing methods on the planet, thanks for reading and learning with me, this is Dr. Bob.... out!!