Cinderblock wall - 2 leafs?

I'm going to be starting construction next week on my project studio. My outer walls are cinderblock that I'm guessing are hollow. Well, at least they sound like their not filled when knocking on them. If they are in fact hollow, would that be a 2 leaf wall? And if so, what type of wall should i build for the interior walls for isolation? Thanks

If they sound hollow when you strike them, then that same sound will be carried into the performance of the isolation. The best thing to do is to fill them with sand. Expensive? I don't know. I do know that that will avoid disappointment when you are finished. There is a forum for studio design here. Use it. Good studio building is 90% design and 10% construction. Andre

Thanks for the reply. Filling the already built cinderblock foundation walls really isn't an option either unfortunately :( Any other ideas?

Hey, I went through the exact same thing... 1st I was lead to believe filling the blocks with sand would be the best and only option. I even devised a plan to fill existing Cinder Block cavities with sand how ever... I think it was Eric Dessert (or another expert) chimed in some where here on the forum and stated that a Cinder Block wall is so stiff it will act as one leaf. The increase in mass from filling a cinder block wall will not be worth the effort (I was going to drill 2" holes, wild ass guess drilling near top of cavity just under solid cement header, funnel sand into the cavities and then re seal holes with cement, concrete adhesive and who knows what). SO treat the cinder block wall as the outer leaf wall. Build you decoupled inner leaf walls. It'll take some searching to verify in the threads on the forum. Marc

guitardad72 wrote:

Hey, I went through the exact same thing... 1st I was lead to believe filling the blocks with sand would be the best and only option. I even devised a plan to fill existing Cinder Block cavities with sand how ever... I think it was Eric Dessert (or another expert) chimed in some where here on the forum and stated that a Cinder Block wall is so stiff it will act as one leaf. The increase in mass from filling a cinder block wall will not be worth the effort (I was going to drill 2" holes, wild ass guess drilling near top of cavity just under solid cement header, funnel sand into the cavities and then re seal holes with cement, concrete adhesive and who knows what). SO treat the cinder block wall as the outer leaf wall. Build you decoupled inner leaf walls. It'll take some searching to verify in the threads on the forum. Marc

Hey Marc, Thanks for the info. Well, that gives me some hope at least. I was just thinking solid cinder block would be one leaf, and hollow would be two. I'll look a little deeper into existing threads too. Matt

Drastic wrote:

Well, that gives me some hope at least.

Give us some idea of how much isolation you want and what the entire wall system is. All is not lost, or at least potentially expensive. What type block (weight, %filled, classification) are you using that you heard a hollow sound from? Also, about what frequency would you guess the sound was centered at? I am now responding on two different websites to your questions. Please decide which website to continue on. Keep em coming! Andre

http://johnlsayers.com/phpBB2/viewtopic.php?t=4131&postdays=0&postorder=asc&start=195 Here is a link to my thread discussing the hollow block wall issue. I'm treating them as one leaf. http://johnlsayers.com/phpBB2/viewtopic ... 2428#52428

Thanks for all the responses guys. I had emailed Rod Gervais about this too. He also said to treat the wall as one leaf.