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Thread: Why Not Asphalt?

  1. #1
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    Why Not Asphalt?

    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 ft 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 180F. 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 140F-150F? 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 180F+. 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.
    Last edited by Rudeboy; 08-19-2010 at 11:31 AM.

  2. #2
    gyroscopes and infrared FoxForce's Avatar
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    Quote Originally Posted by Rudeboy View Post
    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.
    Sadly, so did I. I can't even count the times i've read on car audio forum (sometimes written verbatim): "it's just mass loading, that's all there is to it." As a result, I was forced to devise a patent-pending duct tape and rocks deadener. Sadly, YTD sales haven't gotten above 0 yet.

    As nauseating as it gets, repeating the facts over and over does sometimes stick. I've seen many people drop the old, ineffective ideas and ways in favor of better, more valid and effective ways. But, just like anything else, some people are hell-bent on showing the world they apply stupidity with much more force.

    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.
    Cant wait for another solid laugh. The blind leading the blind shall rear it's ugly head again....

  3. #3
    I can't believe the smell of asphalt was not mentioned

    Having done one car with it, in an area with hot summers, I swore never again.

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    Quote Originally Posted by VP Electricity View Post
    Thanks - should have provided the link when I referred to it above.

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    Quote Originally Posted by VP Electricity View Post
    I can't believe the smell of asphalt was not mentioned

    Having done one car with it, in an area with hot summers, I swore never again.
    Same here. I used Peel and Seal in the trunk of my 97 Civic and it took nearly a year for that horrid smell to go away during the hot days. Then again, the smell may still be there, but I sold the vehicle in April, so I wouldn't know.

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    Odor is certainly a problem and I should have mentioned it. The problem is that enough people have reported that they aren't bothered by it to make the question confusing. Someone else comes along and takes the chance and isn't bothered by the smell, believe they have succeeded and make the rounds describing how well it worked.

    The really important thing is that it doesn't perform well at all. To get any result is going to require a lot of material and much more work - both of which destroy the value proposition that is the only reason to consider using asphalt in the first place. It may smell, it has a very good chance of failing but to even get to the point where those issues come into play you have to have already ignored the fundamental flaws that should have eliminated the material from consideration in the first place.

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    Founding Member imjustjason's Avatar
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    OK, let's look at this from a different angle for a minute. Say I already have close to 1,000 sf of Protecto Seal 45, both aluminum backed and the white, and I have three cars that need treatment. I'm pretty confident that it's asphalt based. Is there any way I could get some benefit out of this stuff? I know I could use it on my house's roof, but my neighborhood association might not like that. Could I, say; use SPL tiles for my constrained layer on the floor then go over that with several layers of the protecto seal making sure to seal off the top layer with foil mastic tape? The bad stuff would be under the carpet sealed off from the cabin.

    Just thinking out loud.

  9. #9
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    Quote Originally Posted by imjustjason View Post
    OK, let's look at this from a different angle for a minute. Say I already have close to 1,000 sf of Protecto Seal 45, both aluminum backed and the white, and I have three cars that need treatment. I'm pretty confident that it's asphalt based. Is there any way I could get some benefit out of this stuff? I know I could use it on my house's roof, but my neighborhood association might not like that. Could I, say; use SPL tiles for my constrained layer on the floor then go over that with several layers of the protecto seal making sure to seal off the top layer with foil mastic tape? The bad stuff would be under the carpet sealed off from the cabin.

    Just thinking out loud.
    If you lay down enough of anything with mass, you will eventually build a barrier. The question is: will it be a stable barrier? If you planned to use the vehicle for a few years and then junk it, it probably wouldn't matter. If there is any possibility that you will need to work or have work done on the floor, you'll have a problem. If you plan to sell the vehicle in the future, the new owner will likely have a problem. You really need to be certain that nobody will ever have to clean up the mess.

    I'm really sensitive to this at the moment. My car was a test platform during the review days of SDS. There are probably a dozen products installed, spanning my knowing nothing about this to knowing at least something about what I'm doing. I decided to remove the old stuff and do it right. I have good products and bad products in there, but no asphalt. Even so, working on it here an there, I have spent about 60hours so far and am almost finished with the trunk. The good stuff isn't terrible but there is more bad than good:


  10. #10
    Founding Member imjustjason's Avatar
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    I wonder if the stuff I have is actually asphalt based then. I used two layers of it in a vette I had for seven years. I took every stitch of it out before I sold it and I didn't have a mess anywhere near that. In fact it left behind barely any traces of it at all. I had to clean a few places here and there with lacquer thinner but my hand NEVER looked like that.

    I can see how you would be a little sensitive.

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