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Discussion Starter #1
I have my headliner torn out and had to scrape off the factory stuff glued to the roof. Before I put in the new headliner does anyone have any ideas for a material I can glue to the roof to act as a sound deadener. I figure it would sort of have to be waterproof since there could be condensation. I know about that Dynamat stuff or whatever it is called but it just seems way over priced. I was thinking about the type of material used under the carpet, the 1/8 inch black stuff but don't know where to find it. Any ideas? Thanks
 

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You are right to be worried about condensation. This is a subject I know something about but will refrain from too much technical stuff because even HVAC engineers have a difficult time with it. Ever heard of sick building syndrome? Vapor barriers in the wrong place can cause it.

If air can get to the surface area between the insulation (it can) and the inside of the roof and there is enough temperature difference between the inside air and the outside air (colder outside than the dewpoint), you will get condensation in between the inner roof and the insulation. If the insulation is absorbent, it will get waterlogged. if not, you might just end up with water trapped between the roof and the insulation causing potential rust and or mildew and or water stains. If it was my car, I would have left that original crappy factory stuff where it was. Since that is not a good option here, I might try roofing repair tar spread thick on the total roof area where you have access followed by glued on insulation sections that will not hold moisture. Should be O.K. that way. You might not get everything covered but it should be a satisfactory job. By the way, the same goes for door panels and other places so think before you put any aftermarket stuff in there right up next to the exterior surface. Folow the factory design! Good luck,
-Mark.
 

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Discussion Starter #3
Thanks, the thick tar stuff did cross my mind and that may be what I go with. Although I didn't want the tar stuff to get "liquidy" and dripping onto the top of the headliner if I had the car sitting in the sun in August. If its the same stuff I am thinking then I don't think it gets any thinner but I still didn't want anything falling onto the headliner. I have had my headliner out for a few months thinking about this and wasn't going to tear down the original stuff but animals made a nest at some point and ruined some of the factory stuff. After thinking about it I had to rip it down but didn't think I would have this hard of a time finding a replacement that I felt good about
 

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The dripping down stuff would be a bummer if it happened. The roof on top of your house gets pretty hot too. I doubt it drips off the roof much. Insulation glued to the tar would make me feel pretty good about it. The tar stuff is a decent insulator for sound and temperature by itself as well as being moisture proof. The factory used it in the doors for that purpose and because it makes the doors less "tinny" when closed. Doors get moisture inside all the time. They put holes in the bottom of doors for that very reason. Maybe someone else has a better idea. Good luck,
-Mark.
 

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I don't necessarily have a better idea, but rather a concern about having the inside of the car smell like tar.

What about coating the underside of the roof with POR15 then putting the self adhesive Dynamat on?

------------------
Bret Copsey
'68 Camaro base coupe
'92 Caprice wagon
'98 Malibu
 

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Dynamat makes spray-on sound deadener. You can buy it in aerosol cans or in a gallon size if you have your own compressor. I think the gallon comes with a hose and nozzle to spray with, but not sure. I was going to use the spray on stuff in the doors.
 

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My son bought the spray on Dynamat in an aerosal can. He used it on the inside of the rear inner wheel wells (inside the rear quarter where the windor mechanism is), and on the floor beneath the rear seat on our 67 coupe. It doesn't go very far and was pricey if I remember right. The other thing about it is doesn't spray on in a smooth manner. I think if you sprayed on too much it would end up as a rough uneven surface, almost like under coatings do. I would be concerned about that stuff possibly flaking off or creating bulges beneath the headliner. We were going to use it when I replaced the headliner, but didn't. I finally just replaced the headliner, and didn't tear out the old insulation or put anything new up there.
 

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The Dynamat spray does create an uneven surface if sprayed on thick. I used it on the sheetmetal under the package tray area and under the rear seat and did spray it on thick. Since these areas are covered, the irregular surfance doesn't matter.
 

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Discussion Starter #9
Boy, people's opinions really make you think. I love this board. Stingr69 made me feel good about the tar stuff then using insulation because the tar would be moisture proof. Then bretcopsey brings up the point of the smell, which is a good one if the car sat in the sun on a hot day. I probably wouldn't go with the Dynamat spray because I think it is over priced. I guess there is no perfect material. Dynamat is probably the best but with the roof being about 5 ft by 5 ft or so it would take about $200 worth or Dynamat. I'm determined to find a cheap alternative. Thanks for the suggestions!
 

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residential carpet pad.- 3/8 to 7/16 thick, breathable and installed with latex carpet glue using a 1/16" trowel. anyone know why this wouldn't work? I did this to a different vehicle I have had for five years and it is still there, though I havn't looked to see if there is any rust, I just know it stuck very well.
 

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Discussion Starter #11
I used to install carpets so I thought of that one too. I was thinking of the old style "hair and jute" (sp) padding but they all collect moisture.

How about this to combat the worry of condensation. Applying a good contact cement and gluing sheets of tin foil to the roof. Use a roller to make sure there are no air pockets. Then glue the insulation to the tin foil. The tin foil wouldn't rust but would it create condensation on it also in this situation? How about clear plastic. It sounds like a terrible idea because it will hold the moisture but if there was no air between it and the roof would it? I'm going home, I think I'm tired. Have a good weekend!
 

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You don't want to use anything that is foil backed, as that will hold the condensation. I'm going to use a product called "duct liner" available from HVAC fabracators. It's lightweight and can breathe, preventing condensation buildup. I'm going to glue it in with 3M spray adhesive.
 

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Moneypit, that sounds pretty good to me. The thick mastic glue would coat the metal and have some insulating ability then the carpet pad, which is probably closed cell foam would not allow much air to exchange between the roof and the pad. "Dead air" bubbles are not a problem but air exchange between roof and insulation can be. Unreal, I think the duct liner will give you trouble personaly. Water vapor in the air can pass through to the metal surface. Think about a nice cold glass of ice tea sitting on a picnic table in the summer. The outer surface of the glass represents the inner surface of the roof. The air outside the roof can get colder than the inside of the car. The car has warmer, moister air inside (outside the glass). You wrap a napkin (duct liner) around the glass to insulate it from the moist hot air and it absorbs moisture as it condenses on the cold glass because the material will pass water vapor. Now the napkin (duct liner) will be wet. You have the insulation contained inside the headliner. How long will it take to dry? Just some things to think about as we re-engineer our cars. I like the thick glue mastic coatings idea best. All you need is a small amount of insulation between air/vapor and steel to prevent condensation. Then it just about sound deadener.

-Mark.

P.S. - duct liner works well in A/C ducts because, while the air inside the ducts is at 100% relative humidity after leaving the evaporator coil, the air outside the duct is warmer than the air inside the duct so nothing will condense inside. The insulation is there to prevent heat from passing thru to the inside of the metal duct from the conditioned space (room). If that were to happen, you could have a condensation problem on the outside of the duct. That is exactly why the duct liner is installed on the inside, not the outside. If you insulate the inside of the glass of ice tea, you don't get condensation.
 

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take a look at jcwhitney.com...part number 25ZX0705N
this might be what your looking for..it is mildew resistant and marine approved...could be a cheaper alternative...

Brian
 
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