Neoprene rubber under bottom plate

Hello , I have a question about decoupling the bottom plate of the inner leaf from the concrete slab. I am building in my basement and i have read it here before where it was recomended to just build the new stud walls directly on the concrete slab. My question is 1)How much isolation do you lose from the flanking path that would be created by doing so,since the rest of the house is connected to the slab in some way? 2) I found a rubber company near me that i could get 1/8'' thick neoprene rubber that they are willing to cut 3'' wide for me,is this a good thing to use to decouple the inner walls from the slab? Or does the rubber has to have a certain specification like x amount of pounds per square inch etc. 3) Green glue company sells a product call Joist tape is that a better solution than all the above? Or am i going over board about sound transmitting thru the concrete slab to the upper floor? The studio is going below my family room and kitchen and i am building independent walls and ceiling with 2 layers of 5/8'' gyp board with green glue. Also i already beefed up the cieling joist with 2 layers of 5/8'' gyp with green glue and caulk w/backer rod. I dont have any drawing i am building from Johns small syudio in 3d that is posted on front page . Thanks

I'm sure you'll get differing opinions, but I prefer to have the (treated) bottom plate sealed against the slab. Limits the potential for flanking sound under the plate.

I would not worry about this - first off - the slab is sitting on a surface of earth - which tends to act to damp it - 2nd - the mass itself, there the is the fact that you are going have to penetrate your rubber isolator to attach the bottom plate to hold it in place....... That aside - yes it take a certain material - with a certain density - which has to be calculated according to the weight of your assembly - and I have done this for studios sitting on the 1st floor of a building - not using rubber but using special isolators made specifically for this purpose - and believe me when I tell you that it is not what you think it is - the materials have to be sized (by this I mean the hardness of the materials) for all of the various loads imposed on them to work - if you use super doors as a part of your construction - then the loads can run anywhere from almost 300 pounds to as little as 60 pound in corners - and there is no one material that will cover that wide a range of loads... critical for is to work is that the compression of the should be more than 25% and less than 75% in order to reach the materials center frequency (which should be 10Hz or less) if you over compress you have a transmitter instead of an isolator - and if you under compress you (again) have a transmitter........ Save yourself a bunch of aggravation and a whole lot of money (to get it right) and forget trying to solve a problem that really isn't going to be a problem........

Thanks guys So Rob and Ted,what do you suggest? What should i put under the bottom pressure treated plate, nothing at all? Could one of you point me to a thread here with the sequence ala the drywall/caulk sequence i think Kingfly posted ? What if i put down a bead of caulk under the bottom plate,would that make any sense? Thanks for the quick response and certainly you Rob for the other 100 quetion you took time out to answer for me.

Rivernile wrote:

What should i put under the bottom pressure treated plate, nothing at all? What if i put down a bead of caulk under the bottom plate,would that make any sense?

Yes it would. Consider 2-3 "S" shape beads running the length of the underside of the bottom plate. You would also be sealing the bottom edge of the drywall (between floor and drywall) after installation for added seal protection.

I was talking to a guy and he suggested that that i use homasode (in 3'' strips) on the top of the pressure treaded wood ,then build new walls on top of that. He said the Homasode will reduce the flanking path and act as a decoupler. Just thought i would throw that on the dart board see what you guys think of that idea

I use 13mm (1/2") foam rubber available from any rubber/neoprene store. It makes up for any variation in the level of the concrete. http://www.johnlsayers.com/Guruland/Pages/page2.htm

There's two aspects of this situation. #1 Sealing. There is the need to seal the underside of the bottom plate to guard against flanking. If the floor is smooth, sealant as previously described will work great. If the floor is terribly uneven, perhaps it should be leveled first, then sealed. #2 Decoupling. As Rod clarified, this isn't worth considering. It's intuitive that there may be some goodness to be had, and it's in our human nature to want to deploy more products, but in reality, there will be no practical benefit.

John Sayers wrote:

I use 13mm (1/2") foam rubber available from any rubber/neoprene store. It makes up for any variation in the level of the concrete. http://www.johnlsayers.com/Guruland/Pages/page2.htm

John, I agree with this approach if the floor being uneven is an issue - this issues with sealing from air passage - (and works excellent in that respect) however it does little to nothing for decoupling.......... Rod

Rivernile wrote:

I was talking to a guy and he suggested that that i use homasode (in 3'' strips) on the top of the pressure treaded wood ,then build new walls on top of that. He said the Homasode will reduce the flanking path and act as a decoupler. Just thought i would throw that on the dart board see what you guys think of that idea

I tried to tell you before - and apparently failed to do so effectively - so I will try again, The original plate has to be attached to the floor - that would be a flanking path - on which you then place something meant to decouple (homosote is pretty much crap by the way) and then - in order to make the wall stable you still have to nail through your "decoupler" to fasten the bottom plate - which means you just re-coupled your wall......... As I mentioned - this is not a big deal - if you properly decouple all the rest of the room from the existing structure - this is not going to be a problem.......

Hello Mr Gervais, I hear you loud and clear sir! I have started to do the framing directly over the slab.I am going to use two or three beads of caulk along the bottom of the plate as Ted suggested. John, Thanks for the reading and responding to my post. And just to clarify,the floor is pretty flat and smooth from what i can tell so i don't think that's somthing i have to worry about. Thanks for uploading that small studio in 3d ,cause that's what i am building from i am just streching it to fit my space ecept i am shooting the speakers down the shorter side of room. The reason being, i would have to turn my back to the live room if i didn't and i dont like that at all. Thank guy and the other thing i am going to have a problem with is fire blocking on the top plate of my inner leaf. I am building 1'' away from the existing walls and ceiling,but i am reading through Robs book again to see if i could figure it out.

i am shooting the speakers down the shorter side of room.

Bad idea. Especially in a small studio like that.

The reason being, i would have to turn my back to the live room if i didn't and i dont like that at all.

Simple solution: Video camera in the LR, screen in the CR. Problem solved! Also saves you building a window, which is expensive and a potential source for loosing isolation if not done right.

I am building 1'' away from the existing walls and ceiling,

One inch isn't much. The MSM resonant frequency will be rather high! I guess you don't need much isolation for low frequencies? You normally need at least 4 inches, or you need lots of mass to make up for the missing air gap. So if 1" is all yo have space for, then you need to increase the mass of your walls (unless you don't need a lot of isolation). - Stuart -

Soundman 2020, Your'e saying one inche between studs is not much? I dont get it i thought that the Spring in MSM includes the space between the studs which in my case would give me S= 3.5'' +1''+3.5'' = 8''? And i am using two layers of 5/8'' gyp board with green glue which the test shows that it inproves the T/L in the low freq? And in addition to that i am using fluffy insulation(R-13) inside the walls which i was told by Mr Gervais that also outperforms the mineral wool in the low freq also. Note also that my existing structure was framed out using 2x6'' studs and i also added 1 layer of 1/2'' OSB and 1 layer of 5/8'' gyp board with backer rod and caulk on both layers. And as mentioned erlier that i beefed up the ceiling joist with 2 layers of 5/8'' gyp board with backer rod and caulk on both layers. With this info do you still think i won't get good isolation? Let me know cause i must have misundertood the 'S' in MSM. Also i know its not the best choice to shoot speaker accros shorter side ,but i had a room in new york which was 12'-1/2'' X 16-1/2' and we shot accross the short side and i was happy .The only difference there is the glass was in the front as opposed to the side like this room. And there where no angled side walls as i am planning in this room,only angled back corner walls. I await your views sir. Thanks

I dont get it i thought that the Spring in MSM includes the space between the studs which in my case would give me S= 3.5'' +1''+3.5'' = 8''?

Ahhh! OK. I though you were building inside-out walls! My bad. 8 inches with 2x5/8 on each side and lots of pink fluffy should give you plenty of isolation. Theoretically, your MSM resonant frequency is something like 14 Hz, so that should be pretty good. Sorry If I spooked you! That's what I get for thinking everyone here is building John's inside-out walls! :) - Stuart -

Thanks Soundman2020, You sent me into something there bro! Because i just got done framing today,and after reading your post,i went back downstairs and i just stood there for a while thinking :cen: . Then i went into a John Sayer forum Search panic :shock: And then you replied :yahoo:

What is the wall structure that is yielding a MSM resonance of 14Hz? A decoupled 8" insulated cavity with double 5/8" on each side? I'm trying out Eric's MSM calculator for the first time (thanks to Eric for making this available to us all). I'm getting 44Hz. Is it generally accepted to use a 25 degree angle in incidence in this calculation? Sorry for the hijack. Thanks for the help.