John Sayers' Recording Studio Design Forum

Check out this 1974 civil engineering testing report of Mason Industries' FSN Floating Floor system. For those not familiar with Mason's FSN mountings, they're very similar to Kinetics' Lift Slab Floating Floor Isolator.

I found the test data fascinating. It's a "must read" for anyone considering floating a concrete floor. I think it's also useful for folks like me who wondered if their existing concrete slab can take the weight of a heavy soundproofed room: if a floated slab can take on so much weight, why wouldn't my slab on grade do better? (Meaning, I don't think I have to worry about crumbling my existing garage floor! )

I also find it interesting that on the brochure, it shows three purposes of a floating slab:

1. Vibration Isolation


2. Sound Isolation


3. Impact Isolation

I can't help but notice that in all of these examples, the illustrations are of isolating the upstairs from the downstairs.

Admittedly, the brochure does state:

However, it goes on to say:

This is all good food for thought in the "to float or not to float" debate... But what exactly am I eating here?

I've had a hard time getting as worried about this as Rod, for one thing he's at a corporate level where they absolutely MUST be over cautious or they will be sued for millions, even if no one is hurt at all -

I'm not saying anyone should "throw caution to the winds" here, but here are some real facts -

I had a slab poured in 2/3 of a pole barn a few years ago - 24' x 48' slab in a 36 x 48 barn. From the bottom up, the floor consists of
clay soil

4-5 inches of compacted 3/4" minus crushed rock

5 inch, 5-sack mix concrete slab, ZERO re-bar other than a "bobby pin" of #4 rebar thru each 6x6 creosote-treated pole, to anchor the slab to structure (the mix included fiber-mesh but no steel other than the previously mentioned "keys" - the "haunches" around the perimeter of the slab are about 10" wide and 12 inches high total - again, no rebar other than the keys thru the poles.

I had the contractor go heavy on the gravel to help avoid wicking from the clay (poor drainage) and have yet to see ANY signs of moisture thru the slab (no plastic ANYWHERE) once the cure was complete (did the thin sheet metal test a few times)

Kicker #1 - my backhoe (Case 580) weighs 12,500 pounds, of which about 10,000 pounds rest on the back tires - total "footprint" in both tires would be about 3 square feet. I've had the hoe parked inside the barn on several occasions - no sign of any cracks whatever. This equates to localized loading of over 3000 pounds per square foot.

Kicker #2 - I bought 2 full units of T1-11 5/8" siding about a year after the slab was poured, to be used to finish the rest of the barn once my old studio is removed and the other 1/3 of the slab is poured (and to re-side my house), and I wanted it stored out of the weather; so I set each full, banded unit (55 sheets each unit, IIRC) one on top of the other, on the rails of a "shop crane", otherwise known as a "cherry picker" or engine hoist; these have steel wheels, about 3-1/2" diameter (4 of them) - I "winched" this entire load across the concrete floor with chains and a "come-along", til it was out of my way near the rear of the slab - so there is approximately 5000 pounds of "plywood" (a stack about 6-1/2 feet tall) sitting on steel wheels with a total contact surface of roughly 3 square inches for ALL FOUR WHEELS against this same concrete slab - this translates to point loading of around 1600 pounds per square INCH - STILL no cracks. That stack has been sitting there for 3-4 YEARS.

Granted, I've not put one of these 1600 PSI "pucks" every 3 feet over the entire slab, but if I had this would equate to a total room weight of 36 such "stacks", or about 180 thousand pounds.

Granted, I didn't use the sleaziest "schmuck CON tractor" for the concrete work (sorry Keith) but I'm STILL wondering if there could be a real problem here - I'm too lazy to check back on ALL your posts, Keith - did you mention any actual DAMAGE to your slab (like cracking, upheavals, crumbling, etc)? If so, then I WOULD tend to worry... Steve

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Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...

Thanks for posting your "real facts," Steve. Very interesting indeed!

I'll try to keep most of the talk about my own project in my project thread so that this one can be focused on the strength of concrete and the merits of floating a concrete floor when isolating from adjacent space (the latter being the most curious and pressing question I personally have right now).


Negative, other than a couple of hairline cracks, and some not-so-hairline cracks in "all the right places (i.e., the scored expansion joints where the cracks are supposed to go). The floor is straight and level (except for the intended slope of about 1/8" per foot over most of the entire surface).

Bottom line: I'm no longer very concerned about my existing floor taking the load of a floating concrete floor. I'm simply back to "prove it to me" on the issue of whether or not it is necessary, given that my project is about horizontal containment, not upstairs/downstairs containment: I'm not trying to keep the area below the sound room quiet, since there's no living space in the clay muck under my slab.

Could be you're right; only REAL concern is if your room were going to be sitting on the SAME slab as your neighbor; then, I'd be floatin' fer sure. You WILL get quite a bit of flanking thru your concrete, so your "horizontal" iso won't be super between garage and house unless there's a break in the concrete that completely separates house structure from garage structure... Steve

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Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...

Thanks, Steve.

Are there any published reports, or even published specs by the floating concrete isolator makers, that demonstrate the effectiveness of floating a concrete floor for TL in adjacent spaces?

I'm trying to apply everything that I have learned about what soundproofing is and what soundproofing isn't to this concept as well, and it's been challenging.

We know that three- and four-leaf walls are inferior to two leaf walls, even when the same aggregate amount of mass. We know this because there are test results that prove it. We also know how severe the inferiority is from the test data. From that, we conclude that two leaves are good and three leaves are bad and four leaves are worse. Lord knows we've seen this enough times!



However, I'm not finding any of the same types of data cited here about the benefits of floating a concrete floor for TL in adjacent spaces. I agree that it stands to reason that floating a concrete floor is "better" as it would address flanking along the outer floor. However, again, I'm not seeing the test results that demonstrate "how much better," what factors come into play (e.g., thickness of the original concrete floor), etc.

I would think that if floated concrete floors were so superior to "not," the makers of the isolators would be "front and center" with test results to prove it. The same makers are not shy about other types of test results -- why the apparent silence on this issue?

I took the Auralex U-boats off my list because of their lack of published specs and their subsequent deafening silence on the subject when pressed for more information. As a result, I've taken EPDM off my list as well: no specs, no proof: no use.

EDIT: I just found this document, which does provide more information. Unfortunately, it is not linked from the product main page or the U-Boat Spacing FAQ or the U-Boat Weight Support FAQ. In fact, the latter link illustrates my "no specs, no proof" point the best.

I don't want to make the same mistake in floating a concrete floor if it isn't necessary -- and if it is necessary, I'd like to know how necessary.

I know that I am not the only person here contemplating the "to float or not to float" dilemma. It sure would be nice to have something concrete (no pun intended! ) to demonstrate its effectiveness... And if there is no such thing, then maybe we're just making a lot of well-educated expensive assumptions.......

In closing, I'll share something I exclaimed when Mike and Dan and I got together weekend before last:

"Where are all the people who didn't float a floor and regret it?"

I should also reference Dan Fitzpatrick's "Estimating Flanking thru Concrete" thread on studiotips.com. I referenced it in my own project thread, but it's very relevant to the discussion here as well.

Does this mean since I have a control room I should float no matter what happens with Keith. Dans post on studio tips have alot of points against the floor. But its even more confusing than my posts( to me). How cutting the slab. There was alot of talk of that, but I think one person said if your slab is connected to the outer walls and continuous through the structure you cant. Was that just a theory or a definite "nono" for me.

to briefly summarize the thread sharward mentions above ...

TL for a 4" slab at 63hz is 37db (see thread for references).

The folks on studiotips assure me that flanking TL will be AT LEAST 37db perhaps 41db or so at that freq

the rule of thumb provided by IR-754 (pg 3/pdf pg8) says that as long as the floor performs 5db better than the wall, the wall performance will not suffer from flanking

so, the wall has to provide at least 36db TL at 63 hz, preferably more. above 36db for the wall flanking will start to have its effect, until they are equal at 41db, when the apparent TL will be 3db less.

i've just realized i've had this backwards until now, i've thought that the wall had to be better than the floor. if the wall is "better" the flanking through the floor will dominate.

only once you exceed that wall performance wil the flanking prevent your room system from getting better.

of course, this assumes 63hz data is similar for other frequencies, but 63hz is the lowest freq there is data on.

hope that helps

dan

EDIT: my focus on the low frequencies here assumes that this is all that matters. however that might not be right ... see June 8 post here.

Im looking like you in your new picture right now from reading your last post, Dan. Are you saying I want my walls to be 5db better or worse than the floor? If the walls exceed the floor, than all you will have is the flanking,right?. than that kinetics underlayment and a cool floor on top could maybe hide that.
If the walls are less than the floor you wont hear the flanking because your walls are suckin, right? thats seems worse,right?

yeah that's one of those areas where my brain starts to stall out.

it's like this.

you can make the wall "better" than your floor, but you will waste your time because of the flanking. the system will not exceed its weak link, the floor.

you can make the wall "equal" to the floor, the performance of the system will be 3db less than what you'd expect from the wall -- or the floor -- by itself. because the poor performance of each combine together.

you can make the wall "worse" than the floor (~5db), in which case the performance of the wall will be about what is expected of the wall.

so you're better off making them equal, but the return on investment between a 5db worse wall and an equal wall is not very good. you're building a wall 5db better but getting a 2db improvement.

make sense?

dan

ya, but did you read this


its here http://www.johnlsayers.com/phpBB2/viewt ... 7147#27147

If that ends up being it would you make walls better with that in mind?

Also, if I make "equal" walls and say an underlayment product and flooring helps some with the floor. Would I possibly shift into the floors into being better and not lose that 3bd so id get the 5db from (instead of 2db) back from the walls.

Huh??!?

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Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...

Simple.
If I think Im gonna float a floor within my walls. Do I have to build the walls to be equal to the floated floor ?

The second part is if I build my walls equal to the slab foundation as dan suggested and then add a simple floor like an iso foam underlayment and flooring on top. That should make my floor a little better then the wall. If the floor is better than the wall I will no longer lose 3db from them being equal. My theory is this makes his walls less than floor approach and brings it up 5db, or you can look at it as a way to not build an equal wall(5bd better than less "wall") and only get 2db better performance.

Sorry,

It doesn't logically lead to your conclusion.

Your slab on grade could very well be placed over poorly compacted soil in areas......... with a slab itself that was never made to carry that load.

The analysis by a structural engineer on the slab of the studio determined that it could take the loading with a 2' square grid.

In other words - a structural engineer examined the existing construction - I promise you that they did non-destructive testing to determine the size and spacing of the reinforcing within the slab, and - after a careful analysis determined what the slab could safely carry.

And from this you have enough information to determine that your slab on grade won't have a problem?

Just to give you a picture of what a 5 1/2" composite slab can be capable of - I headed the design team for an expansion of a national museum at a military base in CT.

We decided that we wanted to maximize the space within the library - so we designed the slab with the intent of installing movable compact storage (we did the same within the archive storage area).

The slab was designed for a total long term loading of 400 psf.

Let's see now - the typical residence is designed for 40psf of loading in family rooms, living rooms, dining rooms......... and 30 psf in bedrooms.

No loading is even considered for slab on grade in either garages or basements for residential construction. They just pour a 4 or 5 inch slab - maybe with a little reinforcing (typically a roll of 6x6 light gauge wire).

Even slab on grade for commercial construction is based on 100 psf for assembly use group - 125 psf for storage - 50 psf for business - etc.

Please don't jump to conclusions that you have no data to support.

I've said before - it would be a pain to get an entire room finished - and all of a sudden have one section of an elevated slab crack and drop because the slab beneath it dropped a 1/2" or so.

That would be one heck of an expensive fix.

BTW - Steve,

You can't consider your situation - 1st off - the construction technique was above average - 2nd you oversaw the operation.

Most people never see anything having to do with their slabs except the tops. Not quite the same thing.

Hey peeps - you can draw your own conclusions - in all honesty - there probably would not be a problem with one in a thousand slabs - the problem is I can't tell which one is the problem slab from here...............

Sincerely,

Rod

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Ignore the man behind the curtain........

Rod, thanks as always. Your words of wisdom are not always what we want to hear, but they are surely what we need to hear.