Instructables

Auto sound deadening - part II - more matting and using expanding foam

In http://www.instructables.com/id/Removing-internal-auto-trim/ I showed initial steps I took to add some sound deadening to a diesel Ford Excursion. It's a loud car; the 7.3l diesel engine exhaust could definitely use some muffling.

In this -part II- I'll show how I laid self-adhesive aluminum/butyl mat over all the sheet metal in my car's cargo area. I covered that first layer of sound deadening material with a glued-down sheet of ensolite foam to absorb yet more sound energy.

I laid down a double sandwich of those same materials on the floor. Per advice from an expert, Rick McCallum of http://www.raamaudio.com, doubly covering the floor will help most with blocking out sound from under the vehicle.

I also used expanding polyurethane foam to fill in some huge and undoubtedly resonant voids inside my truck's body panelling.

I understand that most people who go to this amount of effort with sound deadening do it for car audio reasons. My primary intent with this project is simply to quiet the interior of the car.
 
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Step 1: After cleaning and prep (see part I) I laid down acoustic deadening mat.

Picture of After cleaning and prep (see part I) I laid down acoustic deadening mat.
I took out all interior trim up to the headliner, cleaned and prepped and then started covering all the exposed metal surfaces I could with acoustic deadening mat.

I used tools I already had on hand. I purchased sound deadening materials from http://www.raamaudio.com and my local Ace Hardware store - please see http://www.instructables.com/id/Removing-internal-auto-trim/ for a full tools and materials listing & some costs. So far the total spend is a bit over $400 and many hours of work.

Here are the sound deadening materials I applied...
DB287041 month ago

Thanks for the instruction. I am about to do something similar with my 81 1.9l turbo diesel AAZ swap VW Truck as well as my 77 TDI swapped Rabbit!
I beleive I may go with #2 marine foam, though.

dchall84 years ago
You can also use roofing patch material.  It's basically the same thing.  Get it at HD or Lowe's. 

You used far more foam than you needed to.  All you have to do is dampen the vibrations on the big flat(ish) metal panels.  The obvious big panels are the trunk and the hood.  The side and door panels come next and the roof if you can get to it.  The flooring is a big panel but it is usually formed to stiffen it.  All you need to do is stick a couple strips of of the aluminized tar paper or a couple lines of foam in an X pattern.  What you did will work but it's just a waste of foam. 

Another approach would be to use a heavy adhesive like that used to hold lineolium flooring down.  Apply it with a slotted adhesive trowel.  This would leave the panel covered with a pattern of stripes.  When they dry they will help damp the vibrations across the entire panel or where you can reach. 
kerns (author)  dchall84 years ago
Thanks for the comment - but with respect, roofing patch material is NOT the same thing. As you note, it's tar based- as a result, it stinks mightily and will melt & possibly slip around in very hot weather.

I agree that it could be used, as could tile mastic or other flooring adhesives, and I've read at least one writeup that mentions someone having used roofing tar sheets extensively. Probably would have been much cheaper than what I used...

But, but, but - the RAAMmat I used is specifically designed for auto sound deadening. There was very, very little odor, and it's tacky butyl rubber with an adhesive layer under soft aluminum composition won't melt and run or possibly even slide completely off in hot weather. We regularly have summertime heat reaching 110+ for weeks on end where I live, so that was a big consideration.

I hear the "too much foam" part of your comment tho, and I completely agree. :-\

 I was however trying for *as much sound prevention as possible*, and I think the overfoamkill and completely covering all panelling with at least two deadening mat layers is definitely accomplishing that. Panels and areas filled with it sound *solid* when knocked on now, versus a hollow echoing tap coming back from unfilled areas.

I'll run out of materials before I can get to it, but the roof and panels inside the engine compartment like the hood are likely suspects for future parts of this extended project.

Thanks again for your comment - good ideas and alternatives!
dll932 kerns2 years ago
I worked for an appliance store many years ago. Whenever they bought a new van, they'd apply mastic to the floor, then stick cut-to-fit 1/2" plywood to it. They did it to strengthen the floor, but I'm sure it quieted the vans down as well.
volksdad3 years ago
HILTI makes a foam product that might work better in this project. First it is hydrophilic, and cures by sucking moisture from the air. Second, you have about a month to use the can- instead of about an hour with the Dow brand. This means you can put layers down and not worry about buckling panels.

You can get it through Hilti, or you can get it at home depot. It's called cf116. Home depot only carries it on the shelves in larger stores. The other stores can order it through the pro desk or you can check home depot online.
expanding foam will just trap moisture and create rust i just had to replace the rocker panels on my truck because the previous owner thought great stuff would be somehow helpful inside the truck. the foam came out shaped like the inside of the panels and the panels fell apart in my hands. i was reading today about some marine stuff that they use for soundproofing motor covers on boats. something like that might work well. and be cheaper then the brand name automotive stuff.
trebornoom4 years ago
i'm interested in your sound deaadening project on the ford diesel.  i have a similar ford diesel.  it too is very noisy, 95dbs going down the highway at 60mph.  did you check the dbs of your ford before and after you finished the project?  i would really like to know how successful you were at reducing the dbs at free way speeds.  i'm not into doing the project myself and upholstery shops cost a lot and have no before and after comparisons.  i would really like to know it is going to help before i spend a lot of $.  regards bob  trebornoom@gmail.com
kerns (author)  trebornoom4 years ago
I can't offer before/after decibel readings, unfortunately - I don't have a sound meter.

Just doing the cargo area and rear side panels yielded "noticeable" results, if that subjective analysis does you any good. '-) I feel strongly that even the project so far has been very well worth the effort.

I haven't had time yet to complete the project with deadening under the 2nd row seating and forward; so far I only also have the left rear passenger door sound insulated. Given how much quieter the rear of the car is now I'm really looking forward to getting the remaining floor and doors done.

Watch out for keeping lock rod travel clear when doing doors... Mine is sticking somewhat on remote control, tho manual operation is fine, and I've got to get back in to free it.