Submitted by trash_recycle t3_10on2zo in DIY

Edit: No. The answer is no this not feasible. Tha j you everyone for your insight.

TLDR: Can I drill holes and spray sprayfoam insulation into a hollow core door to improve sound deadening without damaging the door?

I have more time than money at the moment, such is life for many of us DIYers. I'm also moving careers and will be working from home taking calls and zoom meetings. My partner also works from home and takes calls and meetings. They've established themselves in our livingroom and have been there for the last 2 years, I am taking over a craft room and converting it to an office.

We are fortunate enough to have many (not all, but many) of our interior walls insulated, but I still hear their calls while I'm in the office (you know when someone takes a call, and they just talk a little/lotta bit louder than usual). I'm not ripping out walls to insulate. Buuuuuttt, I couldn't sleep the other night and was thinking about what I could do with the hollow core door.

We have 2 panel hollow core doors which we've already been thinking about setting up a spray booth and painting. I was thinking.... what if I drilled a bunch of holes in the top, bottom and side that faces the hinges. Got some "great stuff" spray foam insulation and sprayed it inside. Scraped, filled, sanded and painted the doors. Would that work? Or would they explode? Or would the corregated internal portions of the doors not allow the spray foam to properly expand? AND if it dis work, would this add to noise reduction.

Thoughts and solutions appreciated, thank you.



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keithcody t1_j6fonbq wrote

There’s usually a cardboard honeycomb inside the door to strengthen it. You probably can’t spray foam very far


Swigy1 t1_j6gw8vy wrote

In addition, you need mass to stop sound if the item is not absorbent, such as an engineered acoustic foam. Spray foam won’t do anything.


ezbake_fpv t1_j6fyu2t wrote

Hollow-core doors are not really hollow. It is more correctly corragated-core, as there is usually a skeleton of cardboard criss-crossing inside the door. in other words, the foam won' t be able to spread out.


JonJackjon t1_j6fu52d wrote

In addition to the internal structure only pockets of volume are accessible through a single hole. And more important, foam is hard to control. You run the risk of your door separating due to the trapped expanding foam.

Try hanging a carpet on the door.


VFenix t1_j6grxg7 wrote

Carpet... On the door...? Do people do this? Does it do anything lol


webbitor t1_j6gssg4 wrote

It would absorb some sound for sure. Basically anything heavy, flexible and thick will help.


slvrsmth t1_j6h1j57 wrote

Half the soviet union lived with carpets on the walls, to provide some sound (and little bit of heat) insulation in the crappy commie blocks.

It's not exactly a good solution, but better than nothing.


DaanTheBuilder t1_j6hce24 wrote

All interior designers stem from a job where people decorated the castle walls with carpets.


JonJackjon t1_j6j8se0 wrote

I was thinking decorative carpet and I don't know how many people do this but carpet has the ability to absorb some of the sound. And a decorative carpet may look fine. Remember some folks hang carpets on the wall.

Weird you were down voted.... go figure.


mcarterphoto t1_j6gmlbf wrote

I'd start with the steel-edged rubber weather stripping and a door sweep. Get the thing completely sealed. You could hang a sheet of concrete in place of the door, but sound will travel through all the gaps.

Then, get some Owens Corning 703 insulation - it's like fiberglass, but very stiff and you can cut it into shapes, and it's very dense for its weight. Wrap it in burlap or make 1x lumber frames for it and then wrap those - the burlap keeps fibers from shedding, and you can get all sorts of colors. You can treat the panels like bulletin boards and pin photos/etc. to them. Mount those to the door to fully cover the "hollow" panels. That's what's used in sound deadening panels, bass traps, and corner traps in recording studios and is a popular DIY sound deadener. All of that may not make a huge difference though, soundproofing requires a lot of density and air sealing. Putting acoustic panels on walls and ceilings doesn't soundproof a room, it just deadens sound reflections. (I do a lot of video and music editing; my office space has 703 panels hanging from the ceiling, in the corners and on the back walls - it's very noticeable when you walk in the room that something's "changed", but if you don't point out that it has to do with sound, it can kinda freak people out).


themostempiracal t1_j6gpowo wrote

This is the answer. Hollow core doors are poor sound blockers but much better than air gaps. Work on installing weatherstripping and door sweeps. Then open the window because your co2 is going to build up and get stuffy.


mcarterphoto t1_j6i7gwg wrote

It's like insulating you home. You can go nuts with fiberglass and house wrap, but one little crack letting cold air in will chill a room out very quickly. Inflitration vs. insulation. Similar with sound, though sound travels "through" things (well, transfers through things). There are lots of construction tricks, like for a quiet room use 2x6 headers and floor plates and frame with 2x4's staggered, so the drywall of both sides isn't physically connected except for the top and bottom. Double up the drywall for more density with the seams staggered. Then fill the space with rockwool or 703 (if you can afford it). But to really have a soundproof wall, far as I know you'll use blocks and fill the voids with concrete.


marigolds6 t1_j6j5fck wrote

>You can go nuts with fiberglass and house wrap, but one little crack letting cold air in will chill a room out very quickly.

Or, conversely, why throwing down a simple draft blocker or tacking up a single piece of rigid insulation in the right spot, or even just putting plastic film over a key window, can make a huge difference in a room.


mcarterphoto t1_j6jipkg wrote

That's why there's one outlet in my house that gets blue tape over it when it's freezing out, it almost whistles cold air in! (Yeah, I need to fix that properly...)


PetuniaFungus t1_j6ftijt wrote

By the time you count time and effort, I think youd be better off buying a hollowcore slab


patssle t1_j6gpzmi wrote

Solid core molded doors aren't that expensive, maybe you can even get it without the door frame and save more money. Home Depot or Lowe's can custom order it.


vinnyboyescher t1_j6g1iph wrote

No, its all little pockets. Plus, foam doesnt work too well for sound anyways.


ERTBen t1_j6gxigb wrote

If you have a Habitat for Humanity ReStore in your area you can get used doors there super cheap.


marigolds6 t1_j6j5xi6 wrote

Be careful of varnished doors though when pulling from donated stock like that, as older door varnish contains lead. (We found this out when we looked into refinishing all the old wood doors in our 1920s house. Turns out it is not something to attempt without really good dust control, even outside.)


GoodGoodGoody t1_j6g7wme wrote

Cheap ugly soundproofing. Glue styrofoam to the inside of your door. Emphasis on ugly.


MET1 t1_j6gmmb9 wrote

Adhesive backed cork squares - available at office supply stores might be an easy, more attractive option.


Azozel t1_j6jmrfk wrote

This doesn't soundproof as much as it reduces echos inside a room, giving the sense that things are quieter without actually preventing noises from entering or exiting the room very much. If you want to sound proof you need denser material. A new threshold and weather stripping on the door is inexpensive and would make a big difference. If you don't want to remove the door then screwing the thickest piece of sheet rock to both sides of the door would help as well.


Azozel t1_j6gtr8s wrote

If you want to deaden sound you need a door with density and a good seal and threshold.

Inside doors really aren't that expensive, about $90-$100. You'll need to cut the door to fit your opening but you can use the old door as a template. You'll also need to chisel out the hinge locations but you can use the old door to see where these go as well. Finally, you'll need to drill out the door handle and again you can use the old door to determine where this should be.


Swigy1 t1_j6gvzx1 wrote

Just last week I replaced all the hollow core doors with solid core in my home. Highly recommend, would buy again, A++

Masonite makes affordable solid core door slabs, and they’re heavy beasts, probably 50lb each. If you’re going to take the doors off, you might as well get those. To finish the slabs you will need:

  • Ryobi hinge jig
  • Milwaukee knob jig
  • Ryobi latch jig
  • Drill
  • Router
  • Hand Planer

I got 6 doors knocked out per day, this included removal, sizing, cutting, painting, and mounting. If it weren’t for the tools and especially jigs, this would not be possible. I also included a video that shows a door vice a guy made. Used that, and it made things way easier.

I made a paint booth in the garage and used a grayco tc pro sprayer, and it has been awesome to use.

When I took apart one of my hollow cores, the hollow core was in fact, not honeycomb but exactly what this video shows. I had been told of dumping sand inside the door. Might be worth a try. But I didn’t like the idea of sand leaking out or stressing the already minimal construction of a hollow core.


FlashHardwood t1_j6g5ezw wrote

Perhaps a DIY sound panel mounted to the door? Foam board insulation, cloth cover.


Deanobruce t1_j6gg6ju wrote

No, I mean yes. But you’d need to drill close to 300 holes and spray.

They doors are filled with a cardboard honeycomb shape. So the foam will only fill one section.


athennna t1_j6gghzf wrote

Just glue one of those sound dampening foam mat things to the inside of the door.


Material_Community18 t1_j6h09ss wrote

Solid core door, or hang a heavy sound-absorbing curtain over the door and as much of the adjacent wall as possible.


compounding t1_j6h2bcb wrote

Expanding foam will split the door if you even slightly overfill any given compartment.

You might be able to use just a spritz of foam to connect the sides and and reduce some of the “drum” vibration of the door, but you realistically aren’t going to fill up significant space with foam unless you are exceedingly slow and careful and go in many many steps.


fantompwer t1_j6gnj3q wrote

Search CL or marketplace for a used door.

Reducing sound transfer requires that you seal all of the gaps first, then add mass and air gaps.


Desperate-Seaweed-44 t1_j6grx8t wrote

Would the work be worth it in the end? How much insulation would you use compared to the price of a new door?


Lucy20230 t1_j6gxv2n wrote

Temporary fix? What if you added grommets or something to a thick packing blanket and hung it like curtains on the inside of the office?


TruCelt t1_j6h9pn1 wrote

Hang a curtain rod above the door. Get some thick (velvet?) curtains that will touch the floor and overlap on the sides. Maybe use a couple of layers if needed. When you have a meeting, close the curtains. The rest of the time you can just sweep them to the side so the door is easy to open and close.


QBFreak t1_j6hg0ch wrote

I know someone who tried to insulate a wall for sound with "Great Stuff." Turns out that once it hardens, it makes an excellent conductor of sound. He was *not* happy with the results. It also expands with a great deal of force. When he sold the place, we ended up having to redo the drywall on that wall because the great stuff had pushed it out a couple of inches at the bottom.

In my experience, expanding foam is not the stuff to use for either sound insulation or in fully enclosed spaces.


Kinggambit90 t1_j6hkzrw wrote

Where you live? I'm in NY and got a place that sells solid core six panel for about 100$. Home depot sells it for around 300$.


bonaroo t1_j6idpuh wrote

I just replaced 3 hollow core doors with prehung solid core doors for 200 apiece. They are very nice. I also invested in some Plantronics headsets that plug into the pc and phone, the sound blocking is good enough that you can speak at a normal volume on calls.


Joe30174 t1_j6ik0h3 wrote

I mean, if you could somehow take off one face of the door and spray every little pocket, then reglue the face of the door back on, lol. But that's ridiculous. I don't think you are going to achieve what you want.


John5247 t1_j6ik2dw wrote

Sound proofing = dense mass materials and sealed gaps and edges. Sound treatment = soft materials applied to the surface. Foam acoustic treatment is not soundproofing.

Go and buy.a fire door and draft proofing strip.


RedJohn04 t1_j6ik647 wrote

No. Buy a new solid core door slab from 84 lumber. Give them the exact measurements for where the door knob and the hinges are. They can order it to the exact size. Add a door sweep for extra buffering.


Mysterious-Ad7019 t1_j6fqgwb wrote

  1. Yes you can.

  1. Ideally, you'd know how the inside is constructed so you can get foam into all the nooks and such, but realistically, only way for sure is to remove one side's panel, spray, then reattach.

If you drill holes, and have an endoscope, you could peek in that way as well.

  1. Otherwise, I'd start with a 1'x1' section, drill the first hole, inject foam, let dry. Then drill the second hole inches away and see if foam has reached that far from the original hole.

Do this a few times and you'll get an idea what hole spacing will allow you to fill fully without gaps.

  1. Thankfully.... Craigslist - for sale - free stuff section often has free solid core doors given away that you can use should you want something "better" without wasting a ton of foam money.

    You'd want 3 hinges on solid cores to support the weight.

  2. Keep in mind - SOUND IS CARRIED BY AIR! If there's any air gaps around the door edges, noise will leak in no matter to how solid that door is.

You'd want to weatherstrip/seal all 4 edges to keep noise out.

  1. Sealing doors in a room that doesn't have a dedicated air return to the heater also means no air flow in or out of that room (air would normally flow under the door out as hot air is blown in from the heater vent).

I'll let you calculate how long three oxygen in a 100% sealed room (meaning it's really sealed well against noise entering) lasts before you die.


Mysterious-Ad7019 t1_j6fqol1 wrote

Normal foam expands a ton, so if you spray into an area that's boxed in internally, it'll bulge/break the panel. Low expansion foam better in this case unless you can remove 1 full door panel from one side to spray in foam.