How To Properly Caulk A Soundproof Wall
May 29, 2023Acoustic Caulk is a key material in soundproofing. It is used to seal all possible air gaps in your soundproof wall design. The internet is full of lots of ways to do this, but what is the best way for your soundproof wall? In this article, we will dive into how to properly caulk your soundproof wall assembly so that it is airtight and will not fail when you finish your soundproofing build.
1) Why Use Acoustic Caulk and Not Regular Caulk or Silicone?
Let's start with why we use acoustic caulk in the first place. Regular caulk or silicone hardens when it drys and is prone to cracking. Acoustic caulk, on the other hand, remains flexible even once it has dried. This means the airtight seal you need will remain many years down the road. Using regular caulk to save money means you risk having small air leaks in your soundproof room that could lead to less isolation over time.
2) Which Acoustic Caulk Should You Buy?
When it comes to soundproofing people have some very strong opinions. I used Green Glue's Noiseproofing Sealant (this is not Green Glue Noiseproofing Compound). I think it worked well. Now some other brands you can research are TMS Acoustic Caulk, Auralex Acoustics STOPGAP, and Tremco Acoustical Sealant. Don't lose sleep over which brand to choose. I might recommend the cheapest so you save some money. They all are acoustically rated and will do the job you need them to do.
3) Caulking Your Bottom Plate
Now, there are a lot of different recommendations when it comes to caulking your wall. In my studio I did not caulk underneath the bottom plate and it was totally fine. However, according to the The Soundproofing Company and Everkem Diversified Products (sealant manufacturer) you should use three beads of acoustic caulk under your bottom plate, one under your first layer of drywall and one under your second layer of drywall. (The Soundproofing Company, Matt Everkemp Products). Below is a diagram from the Soundproofing Company Website that demonstrates this design.
*From the Soundproofing Company Website
Now, I used rigid sill plate gasketing, which is a fancy word for foam that protects your bottom sill plate from moisture and rot. This can help decouple a bit too although that is all theoretical and not lab tested. We could have added acoustic caulk under the sill plate gasketing to add an extra layer of air tight sealant, but I don't think it was necessary in my build. I build my studio on a single concrete slab and am not worried about noise coming up through the earth, the slab and into my studio. However, if you are worried about noise transfer through your floor or slab then I would add the extra acoustic caulk just for good measure.
4) Should You Leave A Gap Where The Wall and Floor Meet?
This is a common question I see on the internet. In my opinion it depends. Again, in my studio I was not worried about resonances from my slab to my drywall, so we put the drywall right onto the slab and used acoustic caulk along the entire perimeter where the drywall meets the floor. I think this is totally fine in this scenario. However, if you are worried about flanking noise paths from the floor to your inside wall then I would employ a different method.
To get maximum isolation from your floor flanking paths I recommend leaving a 1/4" to 3/8" (6-9mm) gap between the drywall layers and your floor. Put backer rod under the drywall to fill the gap and then seal it fully with acoustic caulk. This will help reduce vibrations from the floor to your inside wall and will ensure your gap is airtight. You should do this on your outer wall too.
5) Should You Leave A Gap In Your Corners
The next question you might ask is, should my corner drywall panels touch. The answer, you guessed it, is it depends. In my studio I didn't worry about leaving a gap in my corners because the room is a standalone structure in my backyard. However, if you are worried about vibration from one wall that may have a lot of sound behind it transfering to other walls then creating a gap could help reduce the transfer of sound from wall to wall.
To do this you should leave a 1/4" to 3/8" gap (6-9mm) between your first layer of drywall. Then add backer rod and acoustic caulk to the gap. Next, add your second layer of drywall and leave the same gap. Add backer rod and acoustic caulk to this gap as well. This will ensure the drywall is not touching and transferring sound, but that the gap is airtight and not letting sound through.
6) Should You Leave A Gap Where The Wall Meets The Ceiling?
This is a good question too. If your ceiling is built off your inside wall and is what I call an "independently framed ceiling" then you do not need to leave a gap. The reason is that the frame your drywall is attached to is not connected to the roof or floor above. This means no sound will transfer. If however, you are using ceiling hangers or hat channels for your ceiling design then I think it is a good idea to leave a 1/4" to 3/8" gap (6-9mm) between your wall and ceiling drywall. Do the same design we did for the corners. Hang your first layer of drywall on your ceiling. Then put backer rod and acoustic caulk in the gap. Next, hang your second layer of drywall and put backer rod and acoustic caulk in the second gap as well. This will ensure that sound vibrations traveling from your wall will not connect to the ceiling and sound from the ceiling will not transfer to your walls. Below is a diagram from Home Recording Studio: Build It Like The Pros by Rod Gervais. (Gervais 264)
Conclusion
Caulking your perimeters and beneath your bottom plates is a good idea. If you are worried about flanking paths and noise traveling from your floor to your walls, your walls to your ceiling or your ceiling to your walls then you should leave a 1/4" to 3/8" gap (6-9mm) and fill it with backer rod and acoustic caulk. I hope this article helped clarify this confusing topic about properly caulking your soundproof walls.
Works Cited:
The Soundproofing Company. "Soundproof a wall: Best (Level 3)." The Soundproofing Company, 24 May 2023, https://www.soundproofingcompany.com/soundproofing-solutions/soundproof-walls/spc-solution-3-double-stud-wall.
Matt. "SIMPLIFYING SOUND REDUCTION: FLANKING NOISE AND ACOUSTICAL SEALANTS." Everkem Diversified Products, 9 Oct. 2017, https://everkemproducts.com/sound-reduction-flanking-noise-acoustical-sealants/.
Gervais, Rod. Home Recording Studio: Build It Like The Pros. 2nd Edition, Course Technology Cengage Learning, 2011.
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