A comprehensive guide to sound-deadening a 2018 Third Gen Mazda3 Hatchback
This will function as a one-stop guide to sound deaden the 3rd generation Mazda3. I believe it will be useful for any previous or next-gen Mazda3 owner, or anyone with a CX-30, as these platforms share many components.
Like others undertaking this project, I did a ton of research on sound deadening, the process, and the products first before jumping in. I would encourage anyone pursuing the same project to read through the links I’ve included in this write-up as they should give you all the information you need to sound-deaden your car in a comprehensive, easy manner, without having to do the weeks of research I had to do.
Pre-reading:
If you haven’t already, read through this thread for background as this is a solid, comprehensive write-up.
https://www.mazda3revolution.com/threads/sound-deadening-my-17-mazda-3-bn.242072/
Materials Needed:
1. Butyl-based mat to apply first as your base layer
I used 72 square feet to do the entire car, including hood, wheel wells, full interior, rear hatch area, and all doors. I did not do the headliner.
Total cost: $200 CAD
I used 1 box of 2mm (80 mil) Kilmat, and 1 box of 2.5mm Amazon branded butyl sheets. I found the Kilmat had better adhesion and was easier to cut and work with, because of the smaller sheet sizes, so I used this for tight spaces and the doors. The Amazon stuff was great to apply to large areas such as the floor of the vehicle, because I would just stick one entire sheet down and be done with it. It’s also slightly cheaper than the Kilmat.
Other brands: Silless, which manufactures the closed cell foam, also makes this stuff for a reasonable price.
2. Closed cell foam as the second layer
I used 100 square feet.
Total cost: $200
I did a LOT of research and shopping around to find the best balance between price, value, and performance of closed cell foam. I ultimately landed on using Siless Liner 157mil (4mm) closed cell foam which I found on Amazon. Noico is also another brand that makes this stuff for slightly more cost. These come in boxes of 51 square feet for about $100. I thus bought two boxes of the stuff. I did end up with leftover product, which I have saved as it can be used to stick on anything else that causes noise such as a furnace, washing machine, etc along with the leftover butyl mat.
3. Rubber-based floor underlay as the final layer
I used a 100 square foot roll of Technoflex Underlayment Acoustic Membrane, 2mm thickness.
Total cost: $85
Alternate link: https://technoflexintl.com/en/product/technofloor-acoutstic
Other products I considered, but chose against as the Technoflex is thicker
- https://www.rona.ca/en/product/mono-serra-zito-200-ft2-15-mm-blue-high-density-foam-underlayment-for-vinyl-floors-fm-906-84666069
- https://www.rona.ca/en/product/selitbloc-griptec-subfloor-underlay-pressure-resistent-foam-48-in-w-x-25-ft-l-100-sqft-15-mm-thickness-blue-gold-a64305-05075003
In Canada, you cannot find mass loaded vinyl. My goal was to find something relatively cheap and functional. I went to underlay because it’s sold in bulk and there are many products out there to compare effectiveness. Flooring underlay also has specific requirements in order to carry a particular sound deadening rating. It’s also rubber-based, like vinyl, so I figured I would just double up on layering as I had enough product to do so. I did end up doubling up the layering in most places and had leftover product.
Please note, this product is not adhesive. You lay it down like a blanket and you need to cut it to fit in tight spaces. Thus, I did not use it in vertical areas like the doors. I only used it on the floor and trunk of the vehicle. I am not technically inclined enough to adhere or screw it on the doors, but there are other people in the links on this thread who have done so, so depending on your skill level it is certainly possible.
All Tools Required
- Socket set with 10mm socket and a Phillips screwdriver. I purchased a full socket set because I did not have one and found one on sale.
- E-torx socket size 12 to remove the front seats. I just purchased a set of 8 for $20
- Trim removal tool and plastic clip replacements, approx. $20. Extremely useful!!
- https://www.amazon.ca/dp/B0BVQNVXPZ
- The metal trim removal tool is worth its weight in gold. Trust me, there are a LOT of plastic trim pieces to remove, and this tool makes them very easy to remove properly without breaking anything. All cars nowadays use plastic trim, so it’s a worthwhile purchase if you’re ever going to do work on any future car as well.
- I purchased the set above because it came with a whole array of trim removal tools as well as a huge variety of replacement plastic trim pieces. I ended up using a couple pieces that broke when I did the doors. The kit has everything you may need for most vehicles, including our Mazdas.
- Rubber roller, $12. Useful for rolling down the butyl mat and closed cell foam.
- Do yourself a favor and get some gloves. I used my bare hands for about 50% of the time, and they were sore, and had little nicks and cuts all over them by the time I was done. Much easier with gloves.
Skill Level
I have a general interest in cars but the most technical work I’ve ever done are oil changes and tire swaps. This was the largest and most technical project I ever embarked on. I work an office job, so I don’t even work with my hands a lot. If I can do it, so can you (as long as you set aside the time and have the proper tools).
Results
I did not take before-after videos, as that has been captured by videos on Youtube as well as people who have measured the noise levels in the threads below. All I can tell you is that this does work. In my opinion, the project even for a newb like me is totally worth it. For less than $500, and a couple days of work, you can make your Mazda feel like an entirely different vehicle.
Now, sounds and vibrations are barely transmitted going over rough roads. The car feels so much more planted and stable when going over bumps. The audio system sounds better. The doors close with a rich-sounding ‘thunk’. By far the biggest improvement is getting a whole new level of isolation within the car, which makes long trips so much more tolerable and the daily commute so much more relaxing. I would 100% do this again.
The project
Okay, let’s get to the project itself! I’ve broken up each area of the car into separate sections. As the write-ups below are fairly comprehensive, there is no need for me to reinvent the wheel.
Doors
This link contains pictures and instructions, very clearly detailed, on how to do the doors. I did the rear doors first to get used to working with all the materials, then the trunk, then the interior of the car. I would suggest following these instructions.
https://imgur.com/a/2018-mazda-3-sound-deadener-install-vE1o9Hi
Before taking apart your doors, also read through this thread as it contains some more details and information that you will find useful.
This thread is also good to read as it is very detailed. It is for the previous generation, but the door design has not changed that much compared to our generation.
Wheel arches
Use these links and instructions for the wheel arches
https://www.mazda3revolution.com/threads/sound-deadening.126105/page-2
As well as the Imgur gallery from the Doors section for some more pictures.
Trunk
This is the easiest part of the whole project. If you’ve read the threads above, you don’t need any help with this. I did not do the hatch door. I do not think that is worth it, because if your trunk area is well insulated and you have your rear seat up, there’s not a lot of noise that’s going to get through the hatch door.
Interior
This is the part of the project that I had to figure out on my own, so I want to give several tips that will make it easier if you’re doing this.
~1. Removing the interior carpet:~
First vacuum the carpet.
You don't need to remove the entire console to get access to the majority of the floor. To remove the interior carpet, first remove the rear seat, then the front seats, then the interior plastic trim, and finally there are some pieces of Styrofoam in the front wheel wells. You can pull up the carpet for the left side of the vehicle as you work on that side, then tack it all down, and repeat for the right side of the vehicle.
~2. Removing the front seats~
First, disconnect the battery using the 10mm socket. This is recommended by the manufacturer to prevent accidental discharge of the air bags.
If you have the E-torx size 12 socket, removing the seat bolts is a breeze. I zipped them right off. Undo the back bolts, then slide the seat to its rearmost position, then remove the front bolts. Roll the seat onto it’s back to access the harness, undo the harness, then remove the front seat either from the front or rear door. It doesn’t matter.
Go to this site and download the PDF that Anchorman posted. That is all you need to know to remove the front harness. It took me HOURS of searching the web to find a resource this good – there aren’t even any good videos demonstrating what the PDF shows. https://www.cx3forum.com/threads/drivers-seat-removal.17234/
This was both the easiest and hardest thing about the project. Where I got stuck was removing the wiring harness from underneath the seat. Don’t be like me and stick a screwdriver in there, because that can damage the plastic. Instead, simply lift the white tab, press the tab underneath, and the harness comes off nice and easy. The link above with the PDF by Anchorman is what I WISHED I had at the start. I hope this will make it much easier for you.
Don’t be worried about the airbag going off etc. Using the diagram in the PDF, it’s just 1 harness and it comes off super easy and clips back in super easy too. It’s idiot-proof. You won’t have any trouble.
~3. Remove the interior plastic trim~
Again, watch this video https://www.youtube.com/watch?v=Aat4kUanm9w to see how to remove the trim and in what order. It’s actually quite easy and easy to reinstall as well. Just remember that the front and rear passenger scuff plates go on last. The other interior trim, does not matter what order you reinstall it.
Another tip, when removing the furthermost front inside trim (i.e the fusebox cover) and its equivalent on the front passenger side, there is a plastic nut securing that trim in place at the very front of it. It’s hard to see in there. Simply reach your hand in there, find the nut, and lefty-loosen it all the way until it comes off. Easy peasy!
~4. Remove the carpet~
You can pull up the carpet one side at a time. I recommend starting with the left side. In one area only, I cut through my carpet in order to remove it on the rear passenger areas, where it is affixed underneath the front seatbelt holder. This is not a problem. It was just easier this way, and because that area gets covered up by plastic trim, it doesn’t matter if you cut through it to make your life easier.
Once the carpet is lifted up, vacuum underneath it to ensure you have a clean surface that your butyl will adhere to.
~5. Do the driver’s side first!~
The front left side of the vehicle floor is the hardest to do because you have to contend with the footrest, reaching underneath the steering wheel, and the gas pedal. I removed the accelerator pedal – it is just held in place by two 10mm nuts, and then an electrical harness that easily clips off. Remove it and set it aside. Then, lift the carpet and remove the Styrofoam. Use a needlenose plyer to help unclip the plastic portion holding the Styrofoam in place. I did not end up reinstalling that plastic piece, as I installed sound deadener where it would have plugged into the floor. No harm.
I suggest doing the driver’s side first because once you’re done that front left area, the rest of the car is super easy. So do this while you’re fresh. Try to cover as much as you can in the front wheel wells, because that is a significant area of incoming road noise. Be systematic about cutting the butyl and closed cell foam in the correct sizes here, as you will have to reinstall the gas pedal, the Styrofoam, and the carpet properly. The good news is that it’s all easy to reinstall. I didn’t have any trouble.
Once you’re done with the driver’s compartment, systemically work your way with large butyl sheets and closed cell foam through the rest of the car floor. There is no need to apply this stuff up where the plastic trim will be reinstalled, on the inside lateral frame of the car – if you do so, it might be more difficult to reinstall the carpet and the plastic trim. Just do the flat bottom floor only, and you can hold the carpet up to access up along the centre console as well. (Keep in mind this is written for someone with my skill level – i.e newb. If you are more advanced and know what you’re doing, then go ahead and put some butyl or CCM in the inside lateral area, the area otherwise covered up with plastic trim).
I did not go for 100% coverage. To do that would take a lot longer. I went for about 90% coverage with the butyl and closed cell foam, and the rubber Technoflex layers covered up pretty well 95% of the area.
When you are laying the material down, ensure not to cover the holes for the seat bolts. If you do by accident, no worries – just use a screwdriver to poke through them, and you can easily still thread the bolt through when you go to reinstall your front seats.
Repeat the same steps on the right side of the vehicle.
~6. Reinstall the plastic trim.~
First reinstall the carpet and ensure all the holes line up. Reinsert the plastic clips into the holes to hold the carpet in place. Then, reinstall the frontmost trim piece, ensuring it clicks into place, and finally screw the plastic nut on. You may need to lift the rubber insert around the door to replace the plastic trim properly – the rubber insert comes off and goes on very easily, it is very forgiving to work with.
Then, install the B pillar trim piece. Then, the inside rear trim piece. Finally, the scuff plates, front and rear.
~7. Reinstall the front seats.~
~8. Reinstall the rear cushion.~
~9. Plug in the battery again.~
You’re done! Go for a rest drive and let the results speak for themselves!
Final thoughts
I did not take pictures because I was too busy installing the stuff and there are plenty of pictures available on the various threads.
I did reach out to many people on the forum and on Reddit who have done this project and from everything that I’ve learned, I believe this should be all you need to know to do this project successfully.
It will take several days so set some time aside. Here are some rough estimates:
- Trunk: 2 hours
- Each door: 2-3 hours (first door will take longer, then each door after gets shorter and shorter)
- Wheel wells: 2 hours
- Inside Hood: 1 hour
- Interior: 9 hours. Set aside a full day for this. You will want to take breaks in between steps. It took me from 10am to 8pm.
The left lower part of the above picture, where the yellow arrows point to, is where I made a slight cut to the interior carpet to allow it to more easily lift over. You can see the results of the cut where the orange arrow is (bottom right of photo). When you put the carpet back onto the floor of the car, the cut piece folds back into place, and the whole area is covered with plastic trim, so there is absolutely no loss whatsoever and it is not noticeable.
I did the driver's side first.
When I lifted up my carpet, I did find a mouse nest in the B pillar with two old dried up mice. Who knows how long they'd been in there.
2018 Mazda3 driver door sound deadening
The inside driver's door.
Additions:
About 2 months after I did this job, I replaced the factory tires with Bridgestone Turanza QuietTrack tires. They cost about $1000 all-in. They have made a further improvement, but not as much as I was expecting. I would say about a further 25% reduction in road noise. I got a higher sound reduction from the project than from the tires, but working together, the car is now comfortably quiet for long drives and the main thing you hear now is wind noise, which is not bothersome. I can comfortably say the car is quieter than a 2024 VW Taos.