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Warning: ***DO NOT JUST STICK THE TUBE IN AND START SPRAYING UNTIL YOU SEE FOAM.*** Take a minute and read the product's instructions. I've read the horror stories about using expanding foam and it bulging out your body panels or it overflowed and got onto something and ruined it so you need to be careful and use the proper techniques when doing this. 1) To fill a space, you only need to spray in 50% foam needed to fill it when spraying and let it expand to fill the other 50% over time. 2) You need to insert the tube as deep as possible (or get a longer tube if needed and start with it, you can't change tubes mid-project), spray just enough to fill the space and then start to pull back as you continue to spray if you are also filling a channel as we will be doing on this project. 3) If you have to fill a channel with two open ends, stuff one end with poly fill, open/closed cell foam, fiberglass insulation, newspaper, etc ... so that it doesn't expand out so fast, make sure to push whatever you use in further and let it be pushed out some by the foam. 4) If you need to fill a really big space, go slow and do it in two sessions, cans are one time use only and will seal itself off in a few minutes so buy 2 cans. Knowing how much to use or how far to go with these techniques takes practice and of course, these can be applied to other parts of the car. Before you use foam, THINK about what can go wrong, PLAN what you are going to do and in their steps and THINK about it again because there is no undoing this or cleaning up mistakes once they are made. You need to pay attention to trunk locks, cables, wiring, etc ... and plan accordingly if you need to keep foam away from them. Be ready with the rags and acetone to clean as you go, this stuff is messy.

Materials Needed:
1 can of "Great Stuff - Big Gap Filler"
1 can of "Great Stuff - Window & Door"
Painter's Tape
Acetone (or Gas) to wipe off excess foam, once the foam sets, it's there so clean as you go.
A bunch of rags (I bought a roll of disposable towels at Home Depot)
Plastic drop sheet (DO NOT EVEN THINK ABOUT NOT USING ONE!!!)

OK, on with the show .... At first I was only going to apply deadener to my trunk's exterior panel and the shaded areas show the best that you can do to the exterior panel of the trunk due to the small limited openings. All I could get access to was near the panel's bend which is already stiff so I decided to do the job right, I needed to get to the flat panels so deadener alone was not nearly good enough so I decided to find out about using spray foam (aka Great Stuff) to fill the large pockets and channels.



Holes taped up in the section we will be doing first with drop sheet in place and because of the big/thicker spaces I will be using Great Stuff - Big Gap Filler here ... your mileage may vary. Leave tape on for 24 hours.


We will first be doing the part of the truck lid that is vertical when it is closed so I tied a rope to it and something heavy to hold it in a position that the foam would be going down into the spaces, once I got done spraying, I closed the lid to get the foam as deep as possible. Once you are done with this section, let it set up overnight and start on the other section the next day.


On to the other part of the lid, tape all holes except those that you plan to use to spray foam into. Notice the two holes that the red arrows point out, no foam got to that section so if you have foam leftover after this step, shoot some in there if you need/want to, you might as well use it up. Beside each hole I'm going to use, I placed a piece of tape to cover the hole after foaming it. I will be using Great Stuff - Window & Door to fill the smaller/thinner sections and channels.


Instructions per section numbered on picture. 1) Spray toward the center and rotate clockwise the tube to the outside, then pull back to fill and tape hole. 2) Spray towards the section you just did and rotate clockwise and then rotate back counter-clockwise pulling back slightly, tape hole. 3) Shove the tube (you might need a longer tube, but start with it on, you can't change it mid-project) in as far as you can to try to fill the channel, then pull back as needed. 4) Shove the tube in as far as you can to try to fill the channel, then pull back as needed. 5) You can skip this section or add some if you want to, you can't put a bunch here anyways and really don't need any because there is some factory adhesive there already. Move to the other side of the lid and repeat and leave the lid open for at least a few hours and leave tape on for 24 hours.


Foaming done and don't forget the two other areas pointed out by the read arrows if you have extra foam.
 

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excellent work and tutorial !
I had good results in my wagon with gapfiller. I dynamatted where possible then used the gap filler in areas that I couldnt access or where the 2 sheets of metal were close and could possibly vibrate.
 

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Thanks y'all, the trunk is solid now .... Just go slow, take a practice spray to see the flow rate and think about what you are doing and do not go overboard. Like Jon mentioned, there are some nasty spray jobs out there ... Hey Jon that is Damplifier Pro you see in there, i'm pleased how it's working in the rest of the car. Sam that was my concern too, those panels are really close so Hello Foam! :-D

I still feel the lid is going to need some weight, so i'll more than likely use the Damp Pro on it to add some weight to it.
 

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Discussion Starter #7
For smaller gaps, there is a low expansion version of great stuff.
That is what I used in the 2nd part of the lid and even have it listed in the materials needed ... "Great Stuff - Window & Door"
 

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Discussion Starter #8
I would have added this to the first post but it appears the edit button disappears after a period of time. :/


Even after the foaming, you need to add CLD material to help deaden the trunk lid .... My trunk lid is solid.
 

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First post here... I'm sorry, I'm totally new to this (I want to learn though!) But what is the goal of filling in the empty space with foam?
 

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Discussion Starter #10
The outer skin on the trunk hatch was not accessible so I could not apply the dampening tiles to it so I used the inner trunk's strength (due to it's bends in the metal) and the foam to fuse them into one.
 

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Discussion Starter #12
Cool deal, glad to help .... BTW there is a "Thanks" button in the first post if you would like to use it :D
 

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This is my first post and I am a new member. I am putting a new system in my 2012 elantra and the first time I cranked it up I thought my car was going to come apart. Now I haven’t been into car audio in over 15 years and we didn’t have cool sites like this to refer too. I had good results by using both the spray and regular insulation you find in your local hardware store using a long stick to push the insulation deep into the channels then closed the gag with metal tape that matches the paint. After I got all the channels good and sealed off I used 80 square ft of dynamat extreme to finish the job, the only visible sign of the mat is on the torsion bar. I followed this up by putting dynamat in the doors. Now my car rocks without any rattles or road noise.
 

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hate to rain on your parade, but foam is not a deadener. It is an absorber. In order to deaden, you need to add weight. Great write up though. My trunk is filled with foam and makes a considerable difference. Been that way for 7 years.
 
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