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Thread: Sand filled walls

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    Henrik's Avatar
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    Sand filled walls

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    Hello,
    I'm currently making plans for building something that remotely resembles a professional recording studio. My studio construction consultant came up with the idea of filling the studio walls with sand instead of mineral wool. His point was that this would be an inexpensive way to make the wall construction dense, and thus more soundproof. Of course, getting the sand in there is a bit more difficult than mineral wool. He also suggested we don't use gypsum walls since we could have a disaster if something crashed into the wall and broke it...

    Not that I doubt his skills (he's been building studios for Swedish Radio for 25 years), but I still wanted some comments on this approach, since I've never heard of this construction idea from anybody but him (and I've been doing quite some reading). We have an idea for how to get the sand in there, and all the way up to the ceiling - but what do you think about the sound transmission loss compared to the good old gypsum walls filled with mineral wool?

    Cheers
    /Henrik

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    sheppard's Avatar
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    you need to use kiln dried sand if you decide to do it that way.you also need to keep it completely dry,so you dont end up with mold growing in yer walls.
    it is not un common to fill the underside of a floating floor with sand,but i think i would go with the rock wool for my walls.
    sheppard

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    Michael Jones's Avatar
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    I'd be concerned about the structural integrity of a sand filled wall.
    It would be very heavy, to say the least, and I wonder how the shear stresses from the sand would act on the base plate, top plate and truss system. It would be kind of... top heavy, and if the wall was even slighly out of plumb.... well, you get the idea.

    I'm not saying it wouldn't work, it just seems the shear stresses would be very high.

    A regular wood frame wall that has a brick facade would seem a much more practicle way to go.

    Or, if you're interested in inexpensive mass, maybe look into a "rammed earth" wall system:

    http://www.durango.com/rammedearth/

    http://www.earthhomes.com/rammedearth.htm
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    are you in a basement? better question- is the space in question built on a concrete slab on grade- or are you on an upper level- sand is a good idea if your carefull (moisture definately an issue) - Mr. Jones- are you structural engineer by any chance (sounds like you might be so correct me if im wrong) your wall- assuming its a 2X4 stud wall (3-1/2" thick + sheathing both sides) and assuming that the density of the wall is consistant throughout the cross section of the wall (good assumption since its sand) would have to be out of plumb by 1-3/4" of an inch top to bottom for the forces of nature (vector force of gravity acting in a downward motion from the center of gravity) to cause an eccentricity at the base capable of tipping the wall.

    Moral of the story use an accurate level- problem solved. Unless I missed something Michael? without accounting for dynamic loads (someone or something running into the wall)

    I would reccomend not using gypsum board as your first layer over the studs- plywood or equivilent (particle board 1/2" thick min.) You can put gyp. board over that for a finished look and additional STL.

    Back to the concrete- shear stress will be present where the bottom plate meets the floor- so long as the floor is concrete- 4" thick or better and over solid substraight- sheer should not cause you any problems- if its over a framed wood floor- 2 scenarios- your wall is over a bearing wall below it- or its not- if its not then the problem may be the floor system taking the weight of the wall. If your directly over a bearing wall its not an issue

    Not sure where Michael was going with the top plate and truss system comment- sand is heavy- gravity acts downward- period-

    If youre in a basemnt- maybe consider using concrete block and filling the voids with sand or concrete- would give you a better STL (7-5/8" solid thickness vs. 4-1/2" solid thickness- For a finish just anchor furring strips to the wall and hang drywall over it- tadaaa-

    I hope this is helpfull- (i havent sat through a structures class in a while so hopefully Michael can confirm or deny)- Rammed Earth is an intrigueing concept- worth looking into-

    Jeff

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    John Sayers's Avatar
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    if you fill a stud wall with sand, where do you place the noggins - i.e. the horizontal pieces of 4 x 2 that act as a brace for the frame?

    I go along with the block filled suggestion but the stud wall with sand idea is a bit over the top IMO. I would have thought for a wall of that weight you would need and equivalent support in the slab, as if it were a brick wall. Jeff??

    cheers
    john

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    as long as your block wall sits on a solid conc. floor with a solid substraight- (look for cracks anywhere else in the area- basement whatever- some small cracks=normal, large gapping or alot of cracks = maybe not so good) AND- your new wall will not be more than floor to ceiling (or slightly above ceiling) and carry no load from above (i.e. a floor above) im not an engineer- im an architectural tech- with focus on architectural engineering applications- If your concerned, consult with a local lisenced engineer-

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    Henrik's Avatar
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    Great, thanks for these replies!

    We would definitely use sand that has been burned to get rid of moisture and possibly small creatures living in the sand...

    It's on a concrete floor in a basement-like warehouse storage room (it's on ground level, but that's not what you're asking, right?). But there is an office on the floor over us, so most likely we'll have to make the rooms totally floating, with a new ceiling that is not coupled to the construction. So the sand filled walls would have to support this ceiling, and from what I understand from your comments, this may be the biggest problem with the sand idea. Right?

    So would you please explain a bit more what you mean by a concrete block wall filled with sand? (Language issue, me no be native English speaker ). Not least - won't this get a helluva lot more expensive?

    Of course, if the sand/particle board isn't possible, then I guess we're back where we started, regardless of cost.

    Thanks again. You guys are the best.

    /Henrik

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    My studio (http://www.toddejones.com/hugebuilding.html) is constructed from sand-filled cinder-block. That's an American term for a coarse lightweight oversized brick that has a pair of hollow voids. As you build your wall and alternate the blocks, the voids line up so that you could fill them from the top.

    This has resulted in a large mass and very affordable recording space. It has poor thermal insulation qualities, but I will build making lots of OC703 panels for sound treatment which should have considerable thermal insulative ability.

    I don't know about putting sand in drywall, but I'd worry about the pressure of the sand popping the drywall right off the screws. I'd consider perhaps putting a strong furring strip over the drywall where it lines up over the stud. The screws would go into the furring strip, then through the drywall, then into the stud. It would look weird, but at least it would work.

    Alternatively, you could pursue the approach outlined above, with cinder blocks.

    Cheers,

    -Todzilla
    Insect Massage Therapist
    HUGE sound generation & capture facility
    http://www.toddejones.com

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    Michael Jones's Avatar
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    kremitmusic - I'm a civil engineer. The EIT examination covers a broad range of general engineering principles. The P.E. examination however requires competency in a multidude of disciplines. It's been many years since I took the P.E. but you choose 4 or 5 disciplines from 8 or 10 catagories, and your exam is base around that. Structural was one of the catagories I chose. Both examinations are now required for professional registration.

    While it is true that a column of sand acts in a downward force, there are also competing lateral forces acting on the wall. If the downward force is greater than the lateral force, (which it should be because the wall is "pined" at the top by the truss system, and at the bottom by the plate), then the resultant of those two forces will be in a more downward direction and the wall will stay up! (Did you run a diagram to see at what point the lateral forces would exceed the downward force to come up with the 1 3/4"? Sounds like you did! Good job! I was just thinking out loud at the time.)

    But, what you're not taking into account are "live loads". Wind, rain, snow, and people can have a direct bearing (pun intended) on those lateral forces. Live loads are more difficult to accurately estimate, and that's why many times structural systems seem to be "over-designed".

    Think of it like this:
    There are 2 forces acting on a wall. We'll call them F1 and F2.
    Let's say F1 is a force in this direction:

    ----------------------->F1
    |
    |
    |
    |
    |
    |
    |
    \/
    F2
    And F2 is a force in that direction.

    As you begin to tilt a wall up, F1 is greater than F2. That's why its hard to lift it up.
    But as the wall comes into plumb, F1 diminishes, and F2 becomes greater.
    Like this:

    --->F1
    |
    |
    |
    |
    |
    |
    |
    \/
    F2

    Once you have the wall upright, its easy to hold in place because F1, in theory, goes to zero.
    But F1 never really goes to zero, because true and absolute plumb is unobtainable, it is however, greatly diminished. Now increase the force of F1 in the upright position due to the added mass of the wall, and you can begin to see how F1 becomes greater. F2 also increases, but all F2 has to do is bear on the foundation.
    An analysis of the "moment of inertia" for this system would be interesting to see.

    Add in live or dynamic loads like wind and snow, and you can really begin to see how F1 could be greatly increased over a conventional stud framed wall. Conventional stud framing, with its bolted base plate, and pinned or nailed roof truss, doesn't take into account this increased mass, and increased resultant force of F1 and F2, therefore; additional measures may be necessary to keep F1 in check.

    There are also a multitude of other forces acting on this wall. Most notebly is the force created by the "angle of repose" of the sand. Sand doesn't want to stay in an upright column. It "wants" to spread out in a conical shape. Thats known as the angle of repose. Therefore, the additional forces would look something like this:

    ....f<---| |--->f
    f<------| |------>f

    Where the sand is "pushing" against the sheathing. While those forces are greater at the bottom of the wall, they are still present at the top too, and that could have a small increase to our previously stated F1.


    If at any point in time any of the elements of the entire system weaken or fatigue, due to the increased mass of the wall, then a catastrophic failure could take place. That's true with ANY structural system, but conventional stud framing doesn't have the increased mass that a sand filled wall would.
    Again, I'm not saying it can't be done. It would just require more analysis.


    As far as the sand goes, even if you used kiln dried sand, I'm not sure how you could keep the moisture out of it. Even kiln dried and cured wood studs are not completly moisture free, neither is the sheathing. And during the construction process, any of the elements of the wall section could absorb moisture from the relative humidity of the surrounding air.

    John - In my area, stud frame, 2x4 construction, in a wall 10' high or less doesn't require "noggins" as long as the studs are on 16" centers.
    Last edited by Michael Jones; 01-25-2003 at 09:14.
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    Talking

    Henrik-

    Concrete block (in america anyway) is a modular masonry unit in a variety of sizes- typical here is a block 16"long x 8" tall x 8" deep (sorry not sure what the metric equivilent is) The block has 2 or 3 hollow voids that go through the height of the block- click here for a picture-

    http://www.readingrock.com/read2.htm

    The voids you see in the picture can be filled with anything you want- sand, conc, mortar, chopped up dead people (I dont reccomend the dead people ;-), for a better STL.

    This may cost a bit more- and laying block ( although ive never personally done it) sounds like its a little more difficult- but your also getting almost twice the wall thickness.


    Michael- any thoughts on the floor slab condition with regards to putting such a heavy wall on it- that wall needs to carry the ceiling above it-

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