View Full Version : Solution Found: DIY Sound Insulation & Body Panel Stiffener

A1 A2 German
09-28-2010, 08:42 PM
Some pictures are not for the faint of heart, and most certainly a: Function over form , application.

6 months ago I had posted on Vortex regarding sound deadening my car, and got a lot of very helpful information

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Pat @ Pitt Soundworks

There are three types of deadener products, each with different objectives and results.

1) CLD: constraining layer dampeners
These are a foil liner placed on top of a viscoelastic layer, typically butyl or asphalt based. The rubber base is to help absorb vibrations and the foil layer creates another layer of metal on top of the stock piece which you are applying it to. This has the effect of stiffening the panel, increasing the resonance frequency. It does not eliminate it and only marginally reduces it. It does NOT block sound.

This is your dynamat, fatmat, ss damplifier, peel & seal, etc products. For the most part, these products are worthless. They ad extra weight without any real benefits.......
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Picking up a pair JL 2 12W6V2s created a horrific can of rocks sound emanating from the rear of the uni-body. I was some what surprised after gutting the trunk of the carpeted molds that there was absolute NO sound deadener, insulation or layering of any kind separating the ~17 Gauge sheet metal unibody from the outside world, including the trunk lid. Knocking on the rear quarter panels and deck lid created ting, ting, ting with a very hollowess sound.

Considering just to do the trunk with a CLD would run in the ball park of $300 minimum, and understanding it wouldn't create a solution I held off. Then I recalled a show covering:
Innovations Of The Modern Car, which explained is was a lot more then just the electronics that are making cars leaps of progress, showing how just different welds could take effect, etc . Running down the assembly line showed the robotic arms filling all the voids with an expansion foam, A, B, C pillars, unibody and frame voids and figured, hell, I'll give that a shot. Investigating the voids behind the carpet yielded huge voids, with absolute no structural reenforcement, so, went out and got expansion foam:

Red Arrows Are The Foam Itself
Green Sections Show The Depth Of The Void Sucking Up All The Foam Filling Top To Bottom

Silver Door sized holes opened to quite large voids that would suck down an entire can.
Located in this mess is the infamous Audi Goose Horn, it turned it from a Honk to a Quack http://i41.photobucket.com/albums/e259/Blakelikesfood333/Great%20Stuff/AudiGreatStuffFiller003.jpg
~$3.50 A Can, I use it for everything
See, here I am running naked through the stuff
The width of my hand, also shown in the green, reveals that depth of hollowess voids in the trunk lid which created huge distortion problems from the exterior of the vehicle
The masked X represents the nearest fill point (void) where the expansion foam could be inserted. Removing the rubber garment, left pointer finger, I expected to still find a large void where in turn I could insert the application straw and fill it out. As far as the distance was, removing the garment reveled the entire void filled up all the way to the back of the garment on both sides of the trunk lid, truly expansion foam.

The stuff dries hard, and has structure, yet light as a feather.... here some one dried a large clump of the stuff and carved the head of Rosie Odonald.


The result............................................ ............................................is huge. Knocking on the undone C pillar above the rear quarter panels reveals the tinging that has been problematic. Knocking on the deck lid and rear quarters seriously does not sound like metal any more, not at all, but a hard wood, it's very solid. Solved all the problems, hell, could even make the car cooler in summer.

Draw backs? Just avoid sealing in wiring harnesses but I can't see any others. It's kinda discouraging spraying the stuff as it can be quite a mess, and you'll have to tell yourself function over foam. But as nasty as the stuff can be, I guess it really doesn't matter what the stuff is, when it's truly 100% out of sight as seen here:


There's no visibility of the stuff anywhere once all the carpet went in. And no, it did not separate the weld seams of the car :what:, lol, my car is not bulged or appearing to look like sack of potatoes attempting to work there way out the sheet metal. If I had a more modern car would I still do this?

Yes, but then I probably wouldn't have to since the factory did it.

09-28-2010, 09:32 PM
i like this thread, keep up the good work!

09-28-2010, 10:15 PM
Great write up! Lmk if you want this posted in the DIY section.

09-29-2010, 05:58 AM
Unfortunately that is not structural foam. That is mearly an insulating foam with obvious uses around your house etc. It in no way will stiffen your chassis. They do make 2 part epoxy foams which you can pick up made by several companies that will stiffen your chassis. Oems use it all the time in pillar areas etc. It expands a ridiculous amount. I think fusor and other vehicle sealants companies have their own version. this was something the import world liked for a while and was in all the magazines. Although those voids may be filled there is no strength in that foam. it may however take care of your noise issue. Ill try and find a link to the real stuff.

09-29-2010, 06:52 AM
I know that the skin on the once dried foam is water proof, but I wonder if it will absorb moisture after time.
If it does, then you may have created yourself a future rust problem, similar to what is going on in our front quarter panels.

09-29-2010, 07:07 AM
Very interesting idea. Was just thinking of an easy solution to solve all the rattling..

09-29-2010, 02:37 PM
About how much more weight is added the foam or the structural foam that lotus is talking about?

A1 A2 German
09-29-2010, 06:56 PM
Hello, guys, stiffening the chassis was not my intention, but to stiffen the sheet metal which did a great job at.

I'd be insterested in seeing the real stuff so if you have a link post it up.

As far a water, this stuff wouldn't make it to the housing market if it created all those water problems and would of raised hell with millions and millions of home owners.... especially around wood. But on another note, I stayed away from the drains...but I didn't have too as I live in Arizona.