How much sand to use for floating floor?

Posted: Tue Aug 05, 2008 4:58 pm

I'm going to ask this one final question before I finalize my decision on whether to float a floor or not. This is what the space looks like:
http://recording.org/ftopict-47256-.html

Originally I asked my contractor if it's possible to have sand filling between the 4" x 6" floor joists (with neoprene pads underneath), and he said 4 inches of sand will be too heavy to be safe, since during spring and autumn, the humidity will make it quite heavy.

His suggestion was to use joists that are half the size so there's 50% less sand, and he also suggests mixing the sand with dry concrete to counter the humidity problem. His suggestions sound good in idea, but will it work? Just how much mass does a floating floor need in order to achieve desired sound isolation? Would I even be close to the required mass?

Posted: Tue Aug 05, 2008 8:36 pm

Lunatique,

something has gotten very screwed up in the translations here -

you do not build floating floors with joist and sand fill - I don't know where you ever got that idea - but it is completely wrong.

You can build a deck - and damp it with sand - but this is really only usefull with concrete below - it would not work well with wood framed decks.

If you put down pads and then fill with sand - the sand will run below the frames and make the load transfer to it as well as the pads - and in the end it will all end up turning the deck into a sound transmitter - not an isolator.

The weight has to transfer directly to the pucks them self - and it has to be very considerably in order to get the frequency down around 10Hz - which is really what yuo need.

I explained this pretty much in my book - so I am a little confused by the direction you are heading in here.

That aside - this is not going to work at all - neither will his idea.......

Read all about this in Chapter 3 of my book - I devoted quite a bit of time on this very subject - along with some info on wooden "floating" decks.

If yuo want mass it has to be concrete but it sounds as if that is too heavy for your space.

Rod

Posted: Wed Aug 06, 2008 12:05 am

Thanks for explaining!

So based on the specs of my room (all concrete apartment on the 8th floor), I should just do a normal wooden floor and not bother with any kind of isolation on the floor?

Posted: Wed Aug 06, 2008 7:26 am

No - again you should read that section of my book - or if you don't understand it tell me what is confusing you - a wood floor will act like a drum head - and may even increase transmissions at some frequencies -

it won't solve your problems - and mayincrease them.

If you want to do something to take impact out of the picture try this:

Use 2" of 703 covered with 2 layers of plywood (placed inside the walls of your studio - it will not carry the weight of the walls). Make certain the screws do not fully penetrate the 703. the should not be more than 1" into it.

Make certain to over lap the plywood on the edges at least 2' and use green glue between the layers.

Then caulk the edges where it meets the walls.

If you are carrying a ceiling on your walls it would then be worthwhile to float the walls as well.

Rod

Posted: Wed Aug 06, 2008 7:18 pm

Well, what's confusing me is that it's hard for me to tell based on the text (and in forum posts) what kind of floor structure is recommended for people who live in high-rise apartments. Most of the situations described are garages, basements, typical American wooden houses...etc, and don't usually touch upon multi-floor apartments. And then there's conflicting information all over the web--enough to confuse anyone who tries to dig a little deeper.

So when you say put 2 layers of plywood on 2" of 703, do you mean to leave out the wooden joists completely? Just lay them all flat on the existing concrete floor? I doubt that's what you mean? So with 2" of 703, I assume the joist should be 2x4 or 2x6 and laid down flat?

I dunno, I'm a pretty smart guy, but it seems the more homework I do on this the more confused I get.

Posted: Wed Aug 06, 2008 8:12 pm

Lunatique wrote:

Well, what's confusing me is that it's hard for me to tell based on the text (and in forum posts) what kind of floor structure is recommended for people who live in high-rise apartments.

They are discussed all the time. At most, the construction Rod described.

What are you isolating from with the floor? It is your second floor in your apartment, as you posted on JLS RSD.

It is hard to help you when you keep cross posting.

Andre

Posted: Thu Aug 07, 2008 4:55 am

Luna,

This isn't meant as anything other than a bit of sincere advice, ok? And forgive me if I hijack your thread for just a moment.

Andre' brings up a good point about cross posting to different fora.

This is a fairly small community of good folks who offer advice and help out in the area of acoustics. Most of them are very passionate about what they do, so, they have a tendency to find all the different forums out there.

IMVHO, there are really only about 2 or 3 forums that are worth visiting on a regular basis. Oddly enough, I have discovered that Rod, Andre (both of em'), Ethan, Bob, Glen and Eric, regularly post and offer invaluable help in all 3 of "my top recommended" sites.

What I found was that by posting in multiple forums, I was getting the same answer, from the same people... and only a bit of other viewpoints from a FEW others that don't visit but 1 or 2. Posting to one primary forum concentrates all of your answers to one location... which also makes it easier for the guys who know their stuff, to become familiar with you and what you are hoping to accomplish.

So, I decided on picking Recording.org for my studio build diary. Why? Because a site called recording.org should be a place to find information about acoustics and there just weren't too many builds here... actually, there weren't any full builds being documented here. That, and the fact that there isn't 5000 builds being posted here kinda' means you get a bit more attention to detail from the guys who offer their assistance.

I like our little corner of the world here, and personally hope you'd choose this place for your build thread. As you mentioned, most builds are "typical" basements and bedroom conversions. I would think that yours would be a valuable asset to our community.

[end of hijack]

We apologize for the previous interruption. We now take you back to our regularly scheduled question, already in progress...

Rod really does literally mean put down a 2" layer of OC 703 flat on the floor. Then, lay two layers of plywood on top... no 2x4's, no 2x6's...

I'm going to guess that two layers of 3/4" would be a good choice from a mass standpoint. (tongue and groove subfloor if you can get it) Laying each layer perpendicular would probably be best. That way you minimize seam overlap where sound can (and WILL) get through if not caulked properly.

I guess the best way to think about it is MAM...
Plywood deck (Mass)
OC 703 (Air)
Concrete Floor (Mass)

By not letting the walls touch your plywood/703 floor, the walls are free to vibrate completely independent of the floor. The only problem with this is that while you have reduced impact noise through the floor, your walls are now capable of introducing flanking noise to the concrete that they are resting on.

If you are not expecting to have a very loud music environment, you could possibly use a high durometer neoprene membrane under the wall plates to reduce flanking noise...

You just need to be sure to match BOTH the durometer of the neoprene and it's thickness, to the mass of your walls and ceiling load. You don't want to over or under compress the membrane. Either condition is going to result in less than optimal isolation.

You may want to review Rod's book - pages 52-54, and go through it a coupla' times. I too was seriously fraught with confusion over this "floor" thing.. What helped me was something Eric wrote in another thread... Just keep breaking it down to what is mass and what is air and keep all your assemblies to a simple MAM design... anything else is a waste of time, energy and money.

Posted: Thu Aug 07, 2008 8:30 am

MadMax - I apologize for cross-posting at 3 different forums. I started doing it out of desperation, as early on, I just wasn't getting the help I need, and often my posts will sit there unanswered for weeks at a time, and each day I spend looking for answers, each day the construction of our house is pushed back, and we absolutely must finish the house in October because we have to travel abroad for a few months to deal with some immigration legal issues, and we'd rather not pay rent on our temporary apartment for all those months. It's best to get the house done so we can at least move all of our stuff in before we leave.

I wasn't aware that a lot of the same members visit these forums--I was under the impression only a few guys like Rod did, and I know how busy he can be, so I thought if he missed my post at one forum, he'd find it in another. I really am completely desperate here and I need all the help I can get--especially trying to do this in a city like Fuzhou, and working with people that have no idea what the hell they're doing. The money I'm sinking into the construction is from a loan. I cannot afford to make an expensive mistake. I'll do a quick comparison and see which forum has been the most helpful thus far, and I'll to just that one from now on.

Back on topic.

Wow, so let me get this straight, The 2" insulation lays flat on the existing concrete floor, with 2 layers of plywood (tongue and groove preferred, and joints staggered), and then the finished wood on top . No studs/joists at all, not even at the perimeter to secure the whole thing in place? I think other than leaving a gap to decouple from the walls and then caulking, I'd need to fill the gap with something? Maybe put neoprene pads between the edges of the plywood and finished floor?

I do plan on putting some kind of anti-vibration pad under the walls--some kind of neoprene padding, but I have no idea how to calculate what the optimal load is vs how thick/flexible the pad should be. The people who sell these things here are clueless too--they're just here to sell stuff to make a buck, and they don't know a damn thing about the products, and often you cannot track down anyone who does, and even if you do, the manufacturer usually don't even have test data. If I try to import stuff from outside of China, I'd run out of money before I even finish construction.

That part about mass/air/mass is very helpful. I looked into using sand because I was concerned about the whole resonance thing, as it's been mentioned before that the entire floor might act like a giant drum head. But with Rod's suggestion of not using any joists, I think that problem is taken care of?

Believe me, Rod's book is like a bible, and I've bookmarked a lot of pages to refer to whenever I need to refresh my memory on something. In a perfect world, a book will address any possible situation, but that's just not possible, and that's why I'm here.

I really appreciate you guys helping me out. I hope my experience with this whole thing will turn into a great example that can help others in similar situations, and I hope I do not fail.

Posted: Thu Aug 07, 2008 11:31 am

avare wrote:

What are you isolating from with the floor? It is your second floor in your apartment, as you posted on JLS RSD.

You did not reply to this. From what I can figure out from your various posts, floor isolation is not needed. IOW you would be wasting your money.

I haven't written the following for over a week.

Good studio building is 90% design and 10% construction. The question is not if you can afford to to it right, but if you can afford to do it wrong.

Andre

Posted: Thu Aug 07, 2008 11:40 am

Lunatique wrote:

Wow, so let me get this straight, The 2" insulation lays flat on the existing concrete floor, with 2 layers of plywood (tongue and groove preferred, and joints staggered), and then the finished wood on top . No studs/joists at all, not even at the perimeter to secure the whole thing in place? I think other than leaving a gap to decouple from the walls and then caulking, I'd need to fill the gap with something? Maybe put neoprene pads between the edges of the plywood and finished floor?

DO NOT PUT ANYTHING BETWEEN THE WALL AND THE DECK

You don't want these to touch (the fiberglass is ok - but nothing should touch the wood decking)

Just place them carefully and use backer rod and caulk when you are finished -

BTW it is easier if you do the walls first - finish the drywall taping (with the perimiter caulking of course) and then place the floor inside of that - which gives you an extra seal at the wall bottom.

Rod

Posted: Thu Aug 07, 2008 11:43 am

avare wrote:

What are you isolating from with the floor? It is your second floor in your apartment, as you posted on JLS RSD.

You did not reply to this. From what I can figure out from your various posts, floor isolation is not needed. IOW you would be wasting your money.

I haven't written the following for over a week.

Good studio building is 90% design and 10% construction. The question is not if you can afford to to it right, but if you can afford to do it wrong.

Andre

Sorry about that, I was going to answer it then got sidetracked.

The apartment is 2 floors, and I'll be on the second floor. There will be neighbors above me, but not to the side of me as far as I know. I'm mostly trying to isolate from structural noises like people banging on stuff (people are still moving into other units in the building and they'll be doing construction too, children running around in the living room, wife chopping meat in the kitchen...etc. Also, there's a pregnant woman upstairs so I'd rather not bother her with whatever noise that might come out of my studio flanking through the floor.

Posted: Thu Aug 07, 2008 11:46 am

MadMax wrote:

I'm going to guess that two layers of 3/4" would be a good choice from a mass standpoint. (tongue and groove subfloor if you can get it) Laying each layer perpendicular would probably be best. That way you minimize seam overlap where sound can (and WILL) get through if not caulked properly.

On the laping of joints this is correct - on the 3/4" T&G it is not.

I don't know anyway you wouls ever be able to install 3/4" T&G and then beat it together with a sledge hammer and block without destroying the 703.......

That plus when I did my calcs for compression of the material plus live loads - the double sheets of 1/2" worked fine.

So stick with 1/2" square edge plywood = you can apply metal tape (like they use for duct work) over the joints in the base layer before placing the green glue - and make sure you lar the seams a minimum of 12".. 16" would be even better.

Rod

Posted: Thu Aug 07, 2008 11:47 am

Rod Gervais wrote:

DO NOT PUT ANYTHING BETWEEN THE WALL AND THE DECK

You don't want these to touch (the fiberglass is ok - but nothing should touch the wood decking)

Just place them carefully and use backer rod and caulk when you are finished -

BTW it is easier if you do the walls first - finish the drywall taping (with the perimiter caulking of course) and then place the floor inside of that - which gives you an extra seal at the wall bottom.

Rod

Got it. Thank you so much for helping out! I think your new floor design idea will be quite popular in the next edition of your book, since I can see many people with similar situations like mine would love to use that option. Great thing about it is that it's actually less work!

Posted: Thu Aug 07, 2008 11:54 am

Rod Gervais wrote:

On the laping of joints this is correct - on the 3/4" T&G it is not.

I don't know anyway you wouls ever be able to install 3/4" T&G and then beat it together with a sledge hammer and block without destroying the 703.......

That plus when I did my calcs for compression of the material plus live loads - the double sheets of 1/2" worked fine.

So stick with 1/2" square edge plywood = you can apply metal tape (like they use for duct work) over the joints in the base layer before placing the green glue - and make sure you lar the seams a minimum of 12".. 16" would be even better.

Rod

Unfortunately, I may not be able to find Green Glue here in China, and importing them may or may not work--I'd have to check with customs here. What do I do if Green Glue is not an available option for any part of my construction?

I don't understand what "lar the seams" means. Construction lingo?

Posted: Thu Aug 07, 2008 11:57 am

Understand of course that it is not the same as installing a floating concrete slab and will not give that type of isolation..........

the idea here is to cut out any impact noise - plus the sheathing and green glue do help to an extent in isolate air borne transmissions.

What yuo do underneath in the lower level room is going to be the biggest help for you.

This is also another option - but I am not certain if the materials or experienced labour are available in China - and that is an assembly using a special rubber mat along with lightweight gypsum concrete (which is installed between 3/4" to 1" in thickness and only adds roughly 7 psf of load to your floor).

Rod

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