Author Topic: MLV doesnt work  (Read 16139 times)

Robert Lawton

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MLV doesnt work
« on: December 12, 2003, 01:29:21 PM »
I bought 500 Dollars worth of MLV, put up two layers of it on a common wall in my NYC apt., then covered it with cork. It helps only a tiny bit. Maybe drywall would help but its unrealistic to buy and install in a rental apt. in nyc. This problem is really a nightmare and is driving me out of NY.

andyman91

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Re: MLV doesnt work
« Reply #1 on: April 06, 2006, 09:06:08 PM »
I'm replying because I've been looking into soundproofing options, and I haven't seen many testimonials, positive or negative other than from folks selling product.

My fear is that I, like you, would spend hundreds of dollars and get my hopes up only to find that all the work didn't really solve the problem.

I appreciate the advice I've read here, but I would love to read about results of MLV, Green Glue, or other product, from actual people.

johnbergstromslc

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Re: MLV doesnt work
« Reply #2 on: April 07, 2006, 05:04:06 PM »
Robert:

It doesn't work because you used it wrong.  
Here are the problems you face:

1. No structural decoupling.  Solution:  Convert the common wall into a staggered-stud, double wall or use resilient channels.

2.  No absorbtion in the cavity.  Solution: Fiberglass batts, filling at least 75%.

And since you have all that MLV, reuse it by stapling it to the studs before you start putting on drywall.  Also, make sure your seams are narrow (running them along the studs makes them easier to close) and seal and tape them up too.

3. Inadequate mass.  Solution:  Double (or even triple) up the drywall, after doing steps 1 and 2.

4.  Inadequate sealing.  Solution:  Seal the sucker up.  Any gaps, penetrations or discontinuities.

Then, mud, tape and paint.  

But be aware that some sound will still travel through the ceiling and floor structures, but a lot less.  

You fell for the 'bandaid' fallacy.  You thought you could just throw something up, with little or no effort, little or no construction/demolition and all your problems would be solved.  Doesn't work, does it?

Maeledict

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Re: MLV doesnt work
« Reply #3 on: April 07, 2006, 05:56:16 PM »
John,

I think you missed his point that installing drywall was not an option.  I understand that it's not optimum solution, but when you don't own the property your options are often limited.



I'm in a similar situation myself, so I'm curious if there is any way to get adequate results without rebuilding anything?



For example, using a double layer of MLV with criss-crossing seams caulked, taped or such, what STC rating are we looking at?  I understand that sound will travel through the floors and ceiling, but will there be a noticeable reduction?  Approximately?  Best guess, etc.?



Is there any benefit to using the MLV with foam backing vs the standard MLV?  



If the first layer is stapled to the existing wall and the 2nd layer is applied using only the sticky backing, will it be securely fastened to the wall?



I read that the MLV can be painted.  Does it need to be primed?  Can you use texture as a primer?



Thanks in advance.






johnbergstromslc

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Re: MLV doesnt work
« Reply #4 on: April 07, 2006, 08:07:05 PM »
Yes, I did miss that one.  I guess I was going by the category - there is a dedicated one for renters, and this aint it.  Also, I'm a tad tired today.  Sorry about that.

As for your MLV question, it wouldn't do much at all.  If you're thinking of using 2 layers of the 1 lb/sq.ft. MLV, it is almost the equivalent of putting up another sheet of drywall (2.2-2.4 lb/sq. ft.)  In that case, you will have 3 total sheets on the wall, an increase in mass of 50%.  Using the formula SPL=20 log(mf), you would get a theoretical increase of 3.5 points in the STC, but in reality probably less.  If we're talking lath and plaster walls here, with higher density, the increase will be even less - under 2 dB.  Most people can not discern a change in the sound level less than 3 dB.
The MLV with foam backing is better, since the foam holds it away from the wall and prevents a lot of the vibration transfer and provides a bit of decoupling from the wall.  It might be worth a shot.  And if it doesn't work, you have some nice underlayment for a future carpet/tile installation.  
As for the fastening and painting questions, I have no idea.  Never worked with MLV in that way, but I'm sure somebody else can answer that.

I guess I'm pretty biased, since I'm construction-oriented.  I can't recommend in good faith any of these 'bandaid' solutions.  They're look promising, and make for good marketing, but they don't work that well.  The problem is in the (acoustically deficient) construction.  That's what you have to change to get real, lasting, satisfying results.  Painful (and expensive) but true.

andyman91

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Re: MLV doesnt work
« Reply #5 on: April 07, 2006, 08:09:37 PM »
I figured he might not have done it right.

But your response raises questions still. I've read over & over that we only need to put MLV over existing drywall, seal it , then add another layer of drywall. Sounds pretty much like a band aid to me.

But now I read what i really need is staggared studs, channels, fiberglass batting, and maybe 3 layers of drywall. That's starting to sound a lot more complicated.

I'd still like to hear more testimonials from do it yourselfers.

johnbergstromslc

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Re: MLV doesnt work
« Reply #6 on: April 07, 2006, 09:51:16 PM »
Andy:

The theory with a drywall/MLV/drywall construction is that having the MLV in the center sets up a constrained layer damping system.  And it does, to some extent, especially if you can thoroughly adhere it to both panels and use a minimum of fasteners (zero would be ideal).  But if you simply slap it on top of drywall, it don't do squat, except add a trivial amount of mass to the wall.  If you were to put it on with contact cement and roll it out real good, you could get some 'free layer damping' going on, but it wouldn't be anywhere near as efficient as CLD.  
But if you want CLD, go with Green Glue.  It's designed specifically for the job and will kick MLV's a$$ in that application.  And it's cheaper - $30 per 4 X 8 sheet vs. $45 for the cheapest MLV.

What exactly is your project?  And what stage are you in?  What materials are you considering?

andyman91

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Re: MLV doesnt work
« Reply #7 on: April 11, 2006, 06:07:46 PM »
I haven't started anything yet, but I'm considering two projects, beginning in the bedroom.

1) My downstairs neighbor is fairly audible. It seems like MLV would be better for floors? We're considering getting rid of the carpet and adding a laminate or bamboo floor, and if we do, I'd like to tackle the noise issue at the same time (something that will hopefully help on her side, too, considering we're talking about getting rid of the carpet).

2) my next door neighbor snores at night. I'm thinking about the Green Glue (or MLV) and 1 more layer of drywall.

I'd like to do them both at once. But I don't want to go through that much work & money if it's only going to make a small difference. I'm not up for the channels & staggered studs, etc.

johnbergstromslc

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Re: MLV doesnt work
« Reply #8 on: April 12, 2006, 03:28:45 AM »
Andy:

Hard to say how much difference your alterations will make.  If you get rid of the carpet, you are decreasing the IIC (Impact insulation class) of the floor but if you use the MLV with the foam backing, it's pretty much a wash.  Airborne noise might decrease a bit, if you seal up all the seams properly.  Don't try to use regular MLV, w/o the foam.  It won't do any good.  Your downstairs neighbor will send a flood of complaints your way!    

To get added airborne attenuation, you might try to add some mass to the floor.  Installing Durock or other cement board before the MLV/foam would add 3 lb/sq.ft. (for less than a dollar a sq.ft.) but raise the height of your floor another half inch.  The transition from carpet to hardwood might be a bit harsh...

Adding another layer of drywall to the wall will definitely help if you use Green Glue.

andyman91

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Re: MLV doesnt work
« Reply #9 on: April 12, 2006, 05:41:21 PM »
I have some concern for my downstairs neighbor, but less than for myself! Also, we don't wear shoes inside, so my main concern is lessening what we hear from her.

I had been thinking about cement boards (I'm considering tile in the bathroom). How would they work without MLV?