Why Not Asphalt?

[Rudeboy 152]

Close to half the vibration damping/noise mitigation threads on other forums are debates about using asphalt based materials as a vibration damper. I’ve spent way too much time during the last 5 years typing and re-typing responses to these questions. Let’s keep it in one place to reduce litter and redundancy.

This topic was my introduction to aftermarket “sound deadening”. I had a noisy car, wanted to quiet it down and started to do research. This was 2005. Several respected “authorities” were vocal advocates for asphalt. Part of this came from the belief that products like Dynamat Xtreme were part of a conspiracy to fleece consumers. Part of it was the often repeated “fact” that roofing materials and vibration dampers sold specifically for aftermarket automotive use were exactly the same thing. One cost pennies per ft² and the other dollars so it was worth investigating.

Some of you may remember that Sound Deadener Showdown used to be a testing and review site. Since I wasn’t able to find any conclusive answers on the forums, I decided to buy small quantities of every product I could. Two things were immediately apparent:

1. Nobody had ever had their hands on all of these products at the same time or they would have seen the obvious differences.
   
2. The people claiming that Dynamat Xtreme and roofing materials were exactly the same thing didn’t know what they were talking about.
   

I discovered a few other things very quickly. Many sellers were making outrageous claims. Some were wildly overstating obvious physical characteristics like thickness and mass/area. Others were either claiming outright that their asphalt products were butyl or were using intentionally deceptive descriptions like “rubberized compound” to describe their adhesive layer. Nobody seemed to be drawing the right conclusion from sellers’ attempts to hide the fact that they were selling asphalt.

For several years the argument was about durability. Asphalt had an unhappy tendency to melt or fall off. At the time, there were no reports of butyl adhesive failure – that had to wait a few years until one seller decided to re-purpose some low quality butyl roofing material. I spent a lot of time trying to figure out why this was happening. All of these materials are asphalt with some sort of rubber added to increase heat tolerance. The generally accepted melting point for these compounds is 180°F. That seemed high enough for use in a vehicle, so what was going on?

Our perception of the heat these products are subjected to was wrong. We thought in terms of air temperature inside the vehicle, maybe 140°F-150°F? It turns out things are very different at the sheet metal. Park a car in the sun during the summer, south of the Mason-Dixon line and you can easily get to 180°F+. That explains immediate failures in hot climates.

An insidious part of this problem is that many failures were reported during the second or third summer, many in fairly mild regions. The explanation was pretty simple. The rubber added to asphalt deteriorates over time when exposed to temperatures much lower than those required to melt the fresh material. As the rubber deteriorates, the melting temperature drops. Suddenly it doesn’t take much heat anymore.

The durability question has been answered to my satisfaction. Many high profile asphalt devotees, including some who went to almost insane extremes to install the material “properly” have had their installations fail over the years. A few of the brave ones have come forward and made their results public.

The pennies vs. dollars argument still nags. What if you plan to junk your vehicle after a few years (worse, plan to trade it in and don’t care what problem you are passing on)? Is asphalt a reasonable choice when durability isn’t a factor? Nope.

There are two main reasons people believe they can substitute asphalt roofing materials for CLDs:

1. They look alike – shiny on one side, black and gooey on the other.
   
2. They don’t understand how a constrained layer vibration damper works.
   

See: Caddy Shack, swimming pool scene for all you need to know about point 1. Point 2 needs more consideration. I used to believe that vibration dampers work by adding mass to a panel and lowering its resonant frequency below the audible range. This is completely wrong. They work through a fairly complex sequence of events that occur in the adhesive layer and between the adhesive layer and the constraining layer and substrate. I won’t go into the details here, please see:

Vibration Damping

By Ahid D. Nashif, David I. G. Jones, John Phillips Henderson

The important point is that everything depends on the material property viscoelasticity. Basically this describes something that can be deformed and will then return to its original shape more slowly than it was deformed. The strains created during these events account for the conversion of vibration to heat that we’ve all heard about. Butyl adhesives formulated for vibration damping are viscoelastic. Asphalt isn’t – it doesn’t need to be to seal a roof.

Asphalt adds mass to a panel. It may stiffen the panel, but since stiffening raises resonant frequency, the two mechanisms are offsetting and reduce effectiveness even further. Those who claim to have used it and had good results aren’t giving you the full picture. These claims can be better stated as:

I used asphalt. It was better than nothing. I haven’t used a proper purpose designed vibration damper so I have no basis for comparison. It hasn’t failed yet.

Sometimes the endorsement is explicitly stated:

I used asphalt and it hasn’t fallen off.

Not falling off is a pathetically low standard of performance. Testing I’ve done has convinced me that it takes between 6 and 10 times as much asphalt to achieve something approaching the same result you will get with a real vibration damper. This puts the pennies/dollars question on its head. Add the durability concerns and the huge amount of extra work required and the answer is pretty obvious.

I’m sure some will want to argue the points I’ve made here. If that’s you, please stay away from “I used it and it worked for me”. That’s how we got into trouble in the first place and doesn’t make any more sense than concluding that cigarettes are good for you because your grandfather smoked a pack a day and lived to be 90. If you want to go there, please show us some evidence.

[Julian 641]

Great post Don.

[Kanaworm$ 292]

Sticky!

I vote Don to be on the SSA Tech Team dedicated to the Sound Deadening Forum.

[Aaron Clinton 2,372]

Sticky!

I vote Don to be on the SSA Tech Team dedicated to the Sound Deadening Forum.

Stuck!

[Duran 387]

Or moderator of this section! Excellent post Don, we're all lucky to have such a knowledgeable asset to the forum.

[altoncustomtech 773]

Don, that is a fantastic write up. I enjoyed reading it.

[Rudeboy 152]

Thanks guys.

[Sir-Lancelot 216]

Nicely done Sir.

Thank you.

[Robert.Metzel 4]

Great read! And another point to mention, Asphalt based "dampeners" smell like a freshly paved road. Not something I wanna smell every time I am in the car. Real hot days and the smell is even worse! I don't care what they claim. When I had some the smell never went away!

Don is the man and I use his products! Wont use anything else as long as he is around!

[jcarter1885 995]

Great information man and the last paragraph/analogy was killer, keep up the good work man.

[padoras_box 0]

this was really awesome....it helped and made me watch caddy shack to figure out what you were talking about. anywhay i wam thinking of using something for my car to help with the vibrations and sound. we havent started it yet, but i want to know as much as i can before i start.

[Aaron Clinton 2,372]

Everyone better +1 for this topic.

[stevemead08 752]

its funny how those of us that grew up in the dynomat era dont have a clue as to what a real deadener/barrier really is. atleast myself. back then everything was the same. now we have some great products to chose from. Cheers to Don at Sound Deadener Showdown!

[emh9009 199]

Good read makes me want to learn more about this stuff.

[cedartowndawg 3]

Good read, very informative without being boring. +1 to you, sir.

I do have a question but I'm not sure how well it would fit into this.

Weather stripping?

I'm not sure if it's asphalt based or what but I've heard of a few people using this with supposedly great results. But it seems like it would only add mass since it's not meant for this line of business and like you said, raise the resonant frequency.

Thoughts?

[sefugi 166]

for you sir!!! Look forward to using some of your products in my next build.

[Impious 1,476]

Good read, very informative without being boring. +1 to you, sir.

I do have a question but I'm not sure how well it would fit into this.

Weather stripping?

I'm not sure if it's asphalt based or what but I've heard of a few people using this with supposedly great results. But it seems like it would only add mass since it's not meant for this line of business and like you said, raise the resonant frequency.

Thoughts?

Adding mass lowers resonant frequency, stiffening a panel raises the resonant frequency. So if you add some mass and lower the Fs a little, but at the same time stiffen the panel some which raises the Fs a little, then the net result is virtually no change in Fs If you add mass without stiffening, then Fs will decrease. It takes a 4x increase in mass to decrease Fs by one octave. If you stiffen without adding mass, then Fs increases.

As for results with weather stripping......Don has mentioned over the years as well as in this thread that the viscoelastic properties of the adhesive layer are going determine it's effectiveness as a vibration damper (in addition to some other things). My guess would be that a material designed for the construction industry is probably not going to utilize a compound ideally suited to vibration damping, and that's before we even discuss differences in the other important factors to CLD performance.

But Don could go into much more detail.

Great thread Don!! Sound deadening is one of the areas in this hobby that needs a lot more accurate information being presented and a lot less voodoo and mysticism about what works and why. Glad it was you who stepped up to fill that role extremely well for the past few years.

[Rudeboy 152]

Good read, very informative without being boring. +1 to you, sir.

I do have a question but I'm not sure how well it would fit into this.

Weather stripping?

I'm not sure if it's asphalt based or what but I've heard of a few people using this with supposedly great results. But it seems like it would only add mass since it's not meant for this line of business and like you said, raise the resonant frequency.

Thoughts?

I usually think of weatherstripping as self adhesive foam. Do you mean flashing tape? Some is asphalt, some is butyl and it all has a thin foil layer or no foil layer at all. As Impious stated, an adhesive designed for waterproofing is not going to be ideal for vibration damping. Even though the butyl blends are less likely to fall off, they don't perform any better than asphalt. It's really important to understand that "butyl" is just the base component of these adhesives. It is essentially a synthetic rubber. By itself, it would be a terrible vibration damper. Like rubber, it is almost purely elastic and will simply return any energy it receives. That's why claims of "highest butyl content" and highest rubber content" are silly. That's like claiming your mathematical formula is superior because it use more numbers or your song is better because it uses more notes.

Viscoelasticity is the key to all of this. If anybody is really interested, PM me with a shipping address and I'll send you a sample of a viscoelastic adhesive. There's nothing better than stretching and releasing a viscoelastic material to understand what is going on. Stretch and release it repeatedly and it starts to get warm. Light bulb moment.

I think you'll find that people using flashing tape and reporting great results haven't used a true vibration damper before. With no basis for comparison, a barely noticeable change can be perceived as "great", especially if you've just spent 2 days on the project and really want to believe it was worth the effort.

Impious made an extremely important point for anybody who believes it doesn't matter what you use since you are just "mass loading" - quadruple the mass to lower resonant frequency one octave. That for EACH octave - the second will require 16 times the original mass, and so on.

[cedartowndawg 3]

Ah, thank you for the clarification, Impious.

I guess I misunderstood the part about mass loading and stiffening.

And actually no, Don, I misrepresented, I guess that's the best way to put it because I completely missed the boat, what I was talking about. I looked up the stuff from the video I saw on it and it's called Peel & Seal. A quick search on Lowes tells me that it's aluminum roll roofing. I'm a bit unsure of that but a roll of three feet by thirty three and a half weighs in at only thirty two pounds. So at 32lbs / 100.5 sqft, less than a third of a pound per square foot.

So it seems that it would only stiffen and not so much add mass with that distribution, am I right with that?

Definitely doesn't seem like a good idea to me, but then again, I only now have a very limited understanding so feel free to correct if need be.

Here's a linky to it if you're interested;

http://www.lowes.com/ProductDisplay?partNumber=154032-81326-PS36&catalogId=10051&storeId=10151&langId=-1&productId=3090099

Edited October 1, 2010 by Nick_W

[Rudeboy 152]

Ah, thank you for the clarification, Impious.

I guess I misunderstood the part about mass loading and stiffening.

And actually no, Don, I misrepresented, I guess that's the best way to put it because I completely missed the boat, what I was talking about. I looked up the stuff from the video I saw on it and it's called Peel & Seal. A quick search on Lowes tells me that it's aluminum roll roofing. I'm a bit unsure of that but a roll of three feet by thirty three and a half weighs in at only thirty two pounds. So at 32lbs / 100.5 sqft, less than a third of a pound per square foot.

So it seems that it would only stiffen and not so much add mass with that distribution, am I right with that?

Definitely doesn't seem like a good idea to me, but then again, I only now have a very limited understanding so feel free to correct if need be.

Here's a linky to it if you're interested;

http://www.lowes.com/ProductDisplay?partNumber=154032-81326-PS36&catalogId=10051&storeId=10151&langId=-1&productId=3090099

Peel & Seal is asphalt with a very thin foil facing. You really couldn't find a less useful material for automotive applications - good thing that's not what it is intended for Several people have resold it as sound deadener over the years and one well known brand still does.

[altoncustomtech 773]

I was wondering, in the original test I think I remember that RaamMat was your overall winner in the test results. I've learned alot about sound deadening with your answers to other people's questions over time but mostly originally discovered what it was, how it worked and what not from those tests. As a result I used and recommended the RaamMat for quite some time. Recent months have had me questioning it's true nature anyway. I was curious where it stands now. Is it still a worthwhile product, even if a little less effective, or is it like the many other less expensive options out there and not completely unlike the peal 'n seal.

[Impious 1,476]

I was wondering, in the original test I think I remember that RaamMat was your overall winner in the test results.

Damp Pro was the overall winner.

Raammat was listed as being a good alternative "value" deadener.

[j-roadtatts 1,129]

Would of been nice to see how the SDS compared to the rest. But we know that isn't going to happen.LOL.

[Rudeboy 152]

I was wondering, in the original test I think I remember that RaamMat was your overall winner in the test results. I've learned alot about sound deadening with your answers to other people's questions over time but mostly originally discovered what it was, how it worked and what not from those tests. As a result I used and recommended the RaamMat for quite some time. Recent months have had me questioning it's true nature anyway. I was curious where it stands now. Is it still a worthwhile product, even if a little less effective, or is it like the many other less expensive options out there and not completely unlike the peal 'n seal.

I didn't have any way to test performance when I did the review site. I was really trying to figure out which of the products were what they said the were. At the time, this was important since so many sellers were misrepresenting the absolute basics like what the product was made of, mass/area, heat tolerance and just about everything else. Remember, quite a few were simply taking Peel & Seal out of one box, putting it in another and calling it sound deadener. Some were calling it butyl sound deadener and others were being deliberately misleading with descriptions like "rubberized compound".

I relied on the consensus of forum "experts" and assumed that if many people insisted a product worked, it must. This was a mistake on my part. Getting to the bottom of the gross falsehoods was important, but that's still a pretty low standard to to which to hold products like these. This is what led me to start this business. I started working on an update to the site. I had learned how to test product performance, so that was going to be included. I quickly ran into a dilemma. There are plenty of good products out there, but very few that advocated proper application. I was faced with endorsing a product when the seller was recommending applying it in a manner that was to their advantage and not the consumer's. I'd had enough and decided to try and do better.

I don't want to get into specific competing products, but there are two absolutely critical components to a constrained layer viscoelastic vibration damper. The adhesive needs to be viscoelastic and the constraining layer needs to be capable of constraint No thin foil or no foil facing can do this adequately. That's not to say the constraining layer has to be foil, but since it almost always is, you get the point. Anybody designing a vibration damper should know this. It's safe to assume that if you are looking at a thin foil or Mylar facing, you are actually seeing a flashing material with a reflective facing intended to protect the material form UV damage. Another consequence of this is that the adhesive (butyl or asphalt) is optimized for waterproofing, not vibration damping.

[Aaron Clinton 2,372]

Show me someone from any other brand that has that knowledge and can explain it well to customers.