Feedback please: Filling drywalled partition with concrete...

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...

Guest987

Reply to
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:

Reply to
TP

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

Reply to
tbasc

Wrapping electric boxes in duct tape, gasketing electric face plates, sealing joints at molding, gasketing doors, instlling solid core doors, acoustic insulation inside connecting duct work. These are less dangerous that concrete.

TB

Reply to
tbasc

I think your efforts would go further to look at "no warp" foam. This is a soft white foam that does not generate the pressures that concrete will. One brand would be touch 'n seal:

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If your walls are 8' tall and you fill them to capacity, the hydraulic pressure at the bottom of the "forms" will be in the

1200 psi range. This is hard enough to do with form ply, snap ties, whalers, and stiff backs. Others have noted other reasons to not do this.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

Reply to
DanG

Are you a troll? Listen to what others have said. Commerical insulators have foam products that might be worth looking at. They would fill the voids, which apparently are accessible. Go google < foam "sound insulation" > and read through the 19.8K sites. If you look at the ads, you may even find some do-it-yourself systems. More research appears called for. Measure twice, cut once!

Reply to
royroy

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

Reply to
tbasc

No discussion, suggestions, objections, advice, criticism, ridicule, derision, hate mail, etc., Guest987 . . .

. . . just sympathy.

Jim

(I emphatize with your need, Guest987, for annonimity, but don't expect that to shield you from law suits or gun shots from your concreted-partition-contiguous neighbor.)

JL.

Reply to
lazenby

Oh come on, elaborate why don't you. You're posting anonymously, why not?

You're sure to get better results from masking the sound.

Reply to
John Harlow

not the least of it, but concrete isn't a good insulator for sound.

Reply to
Charles Spitzer

Really? :-)

Nick

Reply to
nicksanspam

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

Reply to
guest987

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!

Reply to
Noozer

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.

Reply to
Bob Morrison

I think you'd get as good or better sound deadening by filling with the wall cavities with granular mica (the little light colored bits in potting soil). It would flow nicely through a small hole and a granular fill would kill the sound better than foam board, concrete, etc.

Reply to
bill a

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

Reply to
Ralph Hertle

Forget about that hairbrained idea.

Install a layer of homosote board on the wall then a layer of gyp board on resilient channels.

Reply to
P.Fritz

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:

thickness (and

isolate and

Reply to
Heathcliff

psf, sorry.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

Reply to
DanG

I am dying to know: What exactly are you trying to mask with this, ahem, creative suggestion of using concrete in your walls? What exactly is the problem?

Reply to
Buck Turgidson

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