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-   -   Encase PVC pipe in concrete for sound control? (http://www.diychatroom.com/f7/encase-pvc-pipe-concrete-sound-control-178145/)

toddmanqa 04-26-2013 01:03 PM

Encase PVC pipe in concrete for sound control?
 
I am in the process of renovating my two-story, plus full basement house, and all the walls and ceilings are open.

There is a second-floor bathroom above the first-floor kitchen, and I am concerned about sound transmission when someone flushes the toilet on the second floor.

The 3" PVC drain pipe for the toilet runs about two feet horizontally between the second floor joists (doubled/tripled 2x8s) before dropping down vertically into a chase on the exterior wall of the house (2x4, furred out to 2x6).

I don't want to rip out the new PVC plumbing that has been put in, and replace it with cast iron, which I've read has much better sound insulation qualities. I've looked into pipe wraps, but they seem to be quite expensive.

Beyond the additional weight considerations, does anyone have any thoughts on the following plan:

On the exterior wall, add 1/2" to 1" of rigid or spray foam to separate the chase cavity from the exterior wall cladding. Starting at the bottom of the vertical chase, add blocking/caulk to make the cavity mostly air-tight. Then, pour concrete in 1' sections around the pipe until I reach the top of chase, and repeat for the two foot horizontal section. The 9 vertical section would rest on the top of the basement wall.

I understand that I will have accessibility issues in the future if there are plumbing problems, but I don't think they would be much different than a PVC pipe buried in a basement slab.


Any comments are appreciated.

TheEplumber 04-26-2013 01:16 PM

The PVC will not be able to expand or contract when embedded in concrete. I would fill the cavity with insulation or buy pipe wrap if you don't want cast iron.

toddmanqa 04-26-2013 04:11 PM

Expansion Issue
 
Thanks for your reply.

I looked at the expansion value of PVC and found that it expands 0.9" per 100 feet for a 25 degree temperature change. I'll likely be installing it in 70 degree weather.

My vertical pipe will only be 90" long, so that means it would expand/contract 0.000675" for a 25 degree temperature change, or about 1/1500 of an inch.

0.90 / 100' x 1 ft/12" = ( 0.90 / 1200 ) * 0.90" = 0.000675, or ~ 1/1500 of an inch if the temperature changes by 25 degrees.

Even if the temperature drops down to -5 degrees (and which seems unlikely if the furnace is working), I'd only be looking at a 1/500 of an inch contraction.

Just to be careful, I will change my plans and I will wrap the pipe in a 1/8" sill plate gasket foam (like what they use on a foundation sill plate).

Oso954 04-26-2013 05:44 PM

I'd just spray foam the entire cavity, or fill it with cut pieces of the 1" rigid foam. It will not only quiet down, but give you better insulation.

If filling chases with concrete was a good idea, other people would be doing it.

jagans 04-26-2013 07:44 PM

Try wrapping it with foam rubber carpet padding and duct tape or zip tie it, and see how that works, you can usually find used stuff for free. :thumbsup:

Javiles 04-26-2013 07:59 PM

Quote:

Originally Posted by toddmanqa (Post 1167759)
Thanks for your reply.

I looked at the expansion value of PVC and found that it expands 0.9" per 100 feet for a 25 degree temperature change. I'll likely be installing it in 70 degree weather.

My vertical pipe will only be 90" long, so that means it would expand/contract 0.000675" for a 25 degree temperature change, or about 1/1500 of an inch.

0.90 / 100' x 1 ft/12" = ( 0.90 / 1200 ) * 0.90" = 0.000675, or ~ 1/1500 of an inch if the temperature changes by 25 degrees.

Even if the temperature drops down to -5 degrees (and which seems unlikely if the furnace is working), I'd only be looking at a 1/500 of an inch contraction.

Just to be careful, I will change my plans and I will wrap the pipe in a 1/8" sill plate gasket foam (like what they use on a foundation sill plate).


applies only to pipe not fittings your not calculating temperature of the mix during the curing proses and pvc is petroleum base those expansion values are good for about 3 years.

wkearney99 04-29-2013 08:41 PM

It's the vertical part, replace it with cast iron. You're wasting effort trying to half-ass something else. Just bite the bullet, rip out the PVC and replace the stack with cast iron. Lordy, it's EASY to do this now when the walls are open! PVC is cheap, it's not like you're wasting a ton of money ripping it out.

AandPDan 04-29-2013 09:27 PM

/\ This!

Replace it with cast iron, problem solved.

I have PVC drains in my house. They are noisy compared to cast iron. I insulated the walls around the pipes using batts, it doesn't do much to help.

Another thing, it's not only the air temp that causes expansion/contraction noises, it's the noise when hot water goes down the drain after cold, or vice versa. That's more than a 25 degree difference, closer to 60 in some cases.

Your math is wrong by the way.

.9" per 100' = .9/100 or .009 per foot of pipe. You have 90" of pipe or 7.5 feet. .009*7.5 = .0675" of expansion in your run, just over 1/16".

Seattle2k 04-30-2013 06:09 PM

Quote:

Originally Posted by AandPDan (Post 1169766)
/\ This!

I insulated the walls around the pipes using batts, it doesn't do much to help.

What kind of batts? Roxul / Rockwool? That's what I'd opt for, as that's one of its common uses...sound deadening.
And then, I'd install Quietrock or a double layer of 1/2" drywall, if possible.

AandPDan 04-30-2013 06:35 PM

I used the JM Acoustic Insulation, it's a fiberglass batt product.

Don't get me wrong the stuff works well. You can't really hear any "noises" from using the bathroom, but when the pipes expand it does so with a "snap" noise.

wkearney99 04-30-2013 06:53 PM

No amount of insulation is going to help when the reverberating material is hard-mounted to the framing. The sound just rings through. Whereas with cast iron the material itself does the absorbing. Trying to stuff insulation around the pipe won't get to the noise that's transferred directly from the plastic to the wood.

The simplest answer is usually the best. RIP OUT THE PVC NOW WHILE IT'S OPEN.

AandPDan 04-30-2013 07:26 PM

Quote:

Originally Posted by wkearney99 (Post 1170277)
No amount of insulation is going to help when the reverberating material is hard-mounted to the framing.

And that's the problem. It needs to be supported somewhere.

Put in the cast iron!!!!

Ghostmaker 05-01-2013 06:58 PM

I like the concrete idea. How will you now handle the extra weight?


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