Feedback please: Filling drywalled partition with concrete...

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I'm really desperate to completely block transmission of any and all sound between two adjacent rooms in my house. (Please don't ask me to explain why. I just have my reasons, believe me.) I know all the "proper" methods to go about re-constructing the common wall for accomplishing this. But I also know that simple concrete is very good at blocking sound. And I happen to have several bags of Post Haste (20 minute set) cement taking up scarce space in my garage that I wouldn't mind using, to this end, to fill the space inside that wall. I have actually thought it through a little deeper than just that. But for now I just want to see what others may think of the basic concept and if there's any reason to believe it cannot (or should not) be made to work. Obvious considerations include: the massive weight of all that concrete on the second-story wood floor supporting the partition to be filled with it; and water-related damage to the drywall from the concrete slurry during the 20 minutes it will take to solidify. (I do have a simple and I believe practical plan, though, for keeping all that heavy, wet concrete from pushing-out and bursting-through the fragile drywall that will have to briefly contain it.)
Thank you in advance for any helpful discussion, suggestions, objections, advice, criticism, ridicule, derision, hate mail, etc...etc... <g>
Guest987
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I wouldn't do it. Sounds like it could create a mess. I have used unfaced batt insulation between rooms. You could blow in cellouse..
TP
guest987 wrote:

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You've got a start: Weight, containing ability of drywall. Add: Moisture, electrical shorts, entombment of wiring in the wall, shri nkage cracks allowing flanking paths for sound.
TB
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My plan for the latter is to apply the concrete in small stages, say one bag's worth at a time, allowing to set, before applying another. For the weight issue, I was thinking of filling about half of the wall's width with 2 inches thick styrofoam insulation, thus halving the thickness (and thus weight) of the concrete.

I wouldn't dare pour in concrete before first taking care to isolate and seal off the electrical. I would install water-tight PVC conduit (plus associated switch and outlet boxes with heavy silicone sealing wherever necessary ) for the wiring.

Cannot these be prevented by putting wire mesh in before pouring the concrete?
Guest987
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This cannot be legit... NOBODY would go to this much trouble to pour a concrete wall using an existing drywall "form".
It would be easier to tear out and use a proper form to start with!
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In a previous post guest987 says...

Overall, this has got to be one of the dumbest ideas I have ever encountered. It would be easier to move to another location than undertake this kind of project.
--
Bob Morrison
R L Morrison Engineering Co
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hehehehehe I agree !!!
--
Bob Morrison
R L Morrison Engineering Co
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JerryD(upstateNY) wrote:

Really! Why not just replace the wall with a *real* soundproof wall that is made to do the job? And did you miss this part:
"Obvious considerations include: the massive weight of all that concrete on the second-story wood floor supporting the partition to be filled with it"
It's on the second story! And what is holding up that floor anyway? For all we know it could be 2x4's every 2 feet. Actually, there is no mention of _any_ wall beneath it, let alone a supporting wall.
--
Tony


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guest987:
My suggestion is that a concrete infill is not a good idea. The paper on the existing GWB will get wet and lose its strength, and the gypsum core material will soften. Ordinarily the GWB would dry out, but the real problem is the hydrostatic pressure of the water laden concrete. The pressure in the lowest 1 ft square area would be 62 lbs per sq. ft. times 8 for the 8 ft. wall. Thats an enormous force, and is sufficient to burst the GWB. Placing the conc. in small pours to allow curing in stages could work, but the hardened material at the top opening would be difficult. The existing GWB will warp when wet due to the pressure.
Instead, apply 1 or 2 layers of either 1/2" or 5/8" GWB to either or both sides of the wall with screws to located studs. That will be faster and stronger. One layer of 5/8" GWB on one side should give a considerable reduction of sound transmission. 3-5/8" of concrete would provide far more result than is really needed.
The fundamentals of sound transmission are simple. One, have no openings in the wall, e.g., duct terminations or convenience outlets. Place SPF in the wall around the J-boxes. Use acoustic caulk at the top, bottom, and side edges or the GWB panels, and tape the joints. Two, the mass of the wall determines the sound absorbing efficiency of the wall. In that respect the concrete is appropriate, however, its placement is difficult though not impossible.
Sound can travel in the under-floor spaces or above-ceiling spaces between joists. Mineral wool insulation between the joists can add mass and limit sound travel., and there are more than one ways to place that. SPF can be optionally sprayed in. Recessed lighting fixtures between the joists should not be covered with any type of insulation.
Three, carpet and pad the rooms on either side. That will lower energy of the frequencies of intelligible speech that may be transmitted.
If you have to use concrete, a retarder in small batches should extend the 20 min. working time. I'd pour only 6-10" at a time in each bay. Small drilled holes at measured heights or measured quantities of mix would work. Larger entry holes for a large funnel at 2 or 3 heights at each bay may work. I would use sand or gravel fines to make a mortar grout and no stone. Several materials can be used to reduce the weight and density of the mortar, e.g., expanded rock or microspheres. Use an exhaust fan to remove water vapor from the rooms and wall for 1-2 weeks. Several bags may not be enough, and the required volume would need to be calculated. If the cement is old or has ever been wet due to bags standing on a garage floor it may not work chemically and not harden. Make a small test batch. All in all, the concrete approach is messier, and that would ultimately require patching of holes. GWB, mud and tape may be less expensive than additional cement. A cost calculation may be in order.
Four. A different approach is to place SPF (sprayed polyurethane foam) in the wall cavities. That is an expensive remedy. That doesn't add much to the mass and doesn't lower the total energy transmitted that much, however, it would lower the transmitted sound frequencies making them less intelligible.
If a music room, for example, is being isolated appropriately add layers of GWB. One or two layers should work.
Ralph Hertle
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Okay. Consider the drywall-as-form idea tossed out then. (I didn't think this particular detail was workable anyway; just wanted to know more before completely ruling it out. Bear in mind though, "placing the concrete in small pours to allow curing in stages" was part and parcel of my idea; thus no need to consider the "enormous force of the hydrostatic pressure...". But thanks for that info just the same.)
Now, out of curiosity, what would you think of the concrete infill idea provided strong plywood be securely screwed over (or, if you prefer, in place of) the drywall?

I'm not clear as to what you are saying here.

And here, are you somehow referring to this wetness and pressure occurring even when "placing the concrete in small pours..."?

Would you happen to know what the weight/mass per square foot 5/8" GWB is these days? (I say, "these days", because I've read that GWB mass density --and therefore its sound absorbing capacity-- is today about half of what it was 30 years ago. See http://www.extremesoundproofing.com/RC_Page.pdf , page 250.)

I know! That's precisely what made me think of it. <g> (BTW, I was planning on only about half that thickness of concrete, using dense styrofoam to fill in the rest of the space.)

I've studied the subject seemingly to death already. I'm confident I have a good handle on the principles of sound transmission abatement (not that I'm unwilling to learn more as I come across more info).

Why should I want to extend the working time? I don't understand.

Yes, I agree. Let me clarify what I posted earlier about the bags of Post-Haste cement I have: this product is premixed (i.e. has the aggregate in it already). So when I said I'd pour "one bag's worth" at a time, I was talking about approx. 12 liters worth. (See product guide at http://www.targetproducts.com/catalog/specsheets/posthaste.pdf .) Given the length of the wall is about 10 feet, that would be close to your 6-10" in each bay. .

The Post-Haste has pea sized pebbles plus sand/gravel fines in it.

I had considered mixing my own concrete using just what you are talking about here (expanded rock/microspheres/etc.) as my first choice. But I came up against an abrupt dead end when I phoned around to try and locate where to buy the materials. Nobody in the various concrete (or plaster and stucco) businesses that I talked to (around my area, of Vancouver, that is) admitted to even hearing about such.

Okay I'm obviously missing something crucial in my concept of how concrete works. You mean not all of the water that goes into mixing concrete becomes _chemically_ incorporated/tranformed into solid concrete compound/s when the concrete has set?

Well I might consider supplementing with something like this if I choose to overcome my present overwhelming urge to do something ASAP, and instead wait a few months until I can properly afford to acoustically modify the wall and pursue methods which, in fact, were my very first choices (i.e. staggered-stud frame reconstruction of wall; plus 1/8" thick lead sheeting sandwiched between two layer drywall shell [or alternatively, single layer of lead-lined "radiation shield" drywall shell --can order lead component thicknesses up to 1/4"], followed by drywall suspended on Gold Bond [aka "hat track"] resilient furring channels.).
Thank you for your civil and informative response...
Guest987
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guest987 wrote:
[clip]

Too much work. Just use GWB.

I was referring to the excess material hardening where ever it splashes, and I should have added that the initial pour could leak onto the floor adjacent or the the ceiling and walls below. The concrete handling is messier than the GWB and would take more labor.

The GWB will immediately soak up water from the concrete. Possibly 25-50% of weight in water added to the GWB.

Read "Walls & Ceilings" magazine for the phone numbers of the GWB makers. That's an excellent technical pro-free enterprise publication, and its free to the trade. Try online for advertiser's phone numbers.
The mass is what governs. There may be something additional said for the modulus of elasticity and rigidity of a material, but higher would mean more efficient transmission at the higher frequencies.

PSF is a bad idea. Again its a lot less work to simply apply layers of GWB.

More power.

You don't want to run out of working time for the time to mix, handle, place, and clean up.

Times the several bays.

Calculate the amount of material on hand and needed. Would GWB cost less than the additional concrete required?

Fine.
Lightweight concrete materials would be used in the floor slabs of high rise buildings. They would probably supply it in the pumped in mix. Check with those suppliers for materials or mfrs. They also use gypsum additives along with the Portland cement.

The GWB will uptake a lot of water before the concrete cures. Not all the water goes into combination with the cement, and would dry out later through the GWB. The excess water needs to be removed and the materials dried out prior to painting.

That's a valid concept to limit higher frequency transmissions - it lowers the rigidity of the wall; but its necessary to also have a high mass.
plus 1/8" thick lead sheeting

That would work OK, but GWB is a lot less expensive per unit mass.
Is the building structure below sufficient to support the additional weight, e.g., no archways, or too weak 28 ga. metal framing?

GWB.
Ralph Hertle
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[...]

Okay, got ya clear this time.

Well my hesitancy with the idea of relying on additional GWB alone stems from personal experience living in basement suite where two layers of 5/8" GWB were installed on the ceiling and all walls. I recall helping my brother -an experienced drywaller by trade, in those days- with the renovation. The result on sound transmission was that there was some muting or dulling of sounds from the people upstairs (i.e. my brother and his family) and between adjacent rooms. But the people who lived in the basement (which included myself for a couple of years) were very frequently annoyed by noise emanating from loud human activity upstairs and/or elsewhere in the house.

The framing is wood. There are no archways, but the weight of the partition rests entirely on the suspended plywood floor. (I.e. there is no supporting or load-bearing wall directly underneath.) I do not know whether the partition rests directly over a joist, or between joists, though. But if the floor was built to standard, I see no reason to believe it could not easily support the additional 160 to 320 lbs. of the lead. (1/8" lead sheeting weighs 2 lb./sq. ft. The wall area is 8' x 10' (approx) = 80 sq. ft.; 80 sq. ft. x 2 lb./sq. ft. = 160 lb.; Double that for the 1/4" lead 320 lb.) Afterall, our livingroom/dining area floor supports two pianos; one upright and one grand. And these have got to be hundreds of pounds each (not to mention that all of each piano's weight is being _concentrated_ at its 4 small wheels [to be exact, only 3 small wheels on the grand]).
Guest987
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Before you begin this, have you throughly analyzed the load-bearing capacity of the supporting structure? The weight you're talking about will far exceed any normal design loads. While immediate failure <may> not be the result, certainly long term the result is most likely going to be ugly, expensive, and perhaps dangerous.
Besides, how are you going to abate the direct transmission path, anyway? You've never described the noise source (and I <think> I've read each of your posts) so I'm still not convinced it would actually solve the problem, anyway.
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Duane Bozarth wrote:

Plus, this is a concentrated load...
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I now have a clearer understanding of the challenges inherent with the concrete infill idea and how, rather than it being an 'as simple as it is crude' down-n-dirty-quick remedy that I had first assumed, it would in fact be a complicated, risk laden adventure at best. I definitely will NOT be trying it.
Guest
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Forget about that hairbrained idea.
Install a layer of homosote board on the wall then a layer of gyp board on resilient channels.

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Listen to Mr. Fritz. The homosote (i.e. fiberboard) - drywall sandwich is the practical and effective way to do this. The concrete is not.
P.Fritz wrote:

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BTW, insalling PVC conduit in walls is illegal in most areas. You would have to use steel conduit.
Please be aware that you are NOT suppose to run romex in conduit either. You use individual strand wires inside of conduit. PVC conduit is normally used outside when dealing with electric.
Tom
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I was aware that romex is not used in conduit. I had no idea it was NOT supposed to be. Is there some kind of safety issue involved here? I recently ran some wiring through conduit in my yard, underground. I used individual strand wires in the conduit. But when the lady of the house suddenly changed her mind as to the numbers of flood lamps, garden lamps, fountain water pumps, power outlets, etc, I realized the wire I had used (12.2) might not be able to supply peak current demands. So instead of trekkting back to the store and buying more single strand wire, I chose to additionally thread through a length of romex (10.2) I had on hand (providing for an additional circuit to connect to). Was that wrong? (<g>)
Guest987
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guest987 wrote:

Unless is was UF, definitely, and if it wasn't I would recommend removing it (eventually, at least) before it degrades--which it will as there will be water accumulated in the conduit...which, if I read you right, if you used conduit the whole run isn't a real good idea, either...
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