Sandwiching MDF and Gypsum Board for Ceiling

[bolehnggak]

Hi,

For my studio, I'm going to put 2-ply gypsum board for soundproofing the ceiling, with rockwools inside the ceiling frame, no channels.
But I'm offered by a friend to buy his unused MDFs, so I'm going to ask you all. How good MDF is compared to gypsum board for ceilings?
I'm thinking of sandwiching a ply of MDF with a ply of gypsum board, which I thought maybe better, since the sound would travel across two different medium. Is it true?
Any comments? Or maybe other suggestions other than MDF and gypsum? Plywood are far more expensive here, so don't suggest that, unless it's really good for soundproofing.

Ari

 

[RICK FITZPATRICK]

How good MDF is compared to gypsum board for

Have you ever lifted a sheet of 3/4"MDF? In fact, consider this. MDF does NOT lend itself to screwing directly through it into the ceiling joists like Gypbd. You would have to precision drill pilot holes to match your joist patern. And then COUNTERSINK for screwheads. Otherwise you are asking for trouble. The screw threads will tighten in the MDF first and will NOT pull the panel up tight to the joists. If you don't believe it, try a sample FIRST. And use HD grabbers with course threads. Preferrably with square recess heads. Not only that, to get tight joints you need a panel or table saw, or if you use a skill saw, use a straight guide and precision layouts. Remember, you only have 3/4" play on the edge connections to fasten to the joists(Joists are 1 1/2" thick. That means with 2 panels meeting at the centerline, you only have 3/4" on either side.) That means to center the screws in this zone, you must drill 3/8" from the edge. Not much to work with. PLUS, your existing cieling joist centerlines would have to be precise and parallel. Otherwise you will end up cutting tapers in MDF. No fun. If you do use it, rent a panel lifter. Believe me. I worked in a Architectural Mill and used MDF extensively. Great stuff for floors, cabinets, or vertical wall situations, but ceiling work would be a real pain in the ass. Personally, I would use 2 different thickness' of Gypbd. Say 5/8" and 1/2". Or a layer of OSB and then Gypbd. Just my .02
fitZ

 

[Michael Jones]

What Rick said!
MDF is NOT the way to go.

I'm using 1/2" sheetrock - 1/2" OSB - 5/8" sheetrock on my walls, and that's still a MAJOR pain to work with. Plus, you need to double up the corner studs to have something to screw into. And those are walls! No overhead lifting.

For the ceiling, I'd go with 1/2" sheetrock and 5/8" sheetrock on RC. That's what I'm doing... or, rather... having done.

 

[knightfly]

Even if MDF wasn't a pain in the ass to put up on a ceiling, it's twice the price of sheet rock. You'll get better results with a thin layer of sheet rock between two thicker ones, and it's cheaper as well as less painful... Steve

 

[RICK FITZPATRICK]

Hello Steve. Say, on CEILINGS, with 3 layers of Gypbd, would you fasten the first layer with minimal screws, as the next layers screws would also help fasten the previous layers? Alternating joints? Caulk each layers joints? How bout RC, will it hold the weight of 3 layers? Seems like the weight would negate the vibration capability of the RC flange, by pulling down on it. Would you float the ceiling gypbd panels between walls, or hang the ceiling gypbd first, so the wall gypbd helps supports the ceiling panels at the wall/ceiling intersection, like normal construction? Normal construction uses no blkng between joists at the wall intersection perpendicular to the joists. How about studio joists? Do you block them? OK OK, I'll stop while I'm ahead!

bolehnggak, knightfly is THE MAN to ask, so I'm picking his brain on your thread while he's here
fitZ

 

[RICK FITZPATRICK]

Holy moly bolehnggak, I just realized your in indonesia. I didn't know you could even get MDF there. Of course, I've never been there. I suppose you can get a Mcdonalds burger too huh How about square head recess screws Sorry bout that, I couldn't resist. Just kiddin with ya! Good luck with the ceiling. And btw, welcome to the bbs.
fitZ

 

[knightfly]

Rick, didn't have the energy to do this twice, so go here for your answer(s) - check the whole thread, your specific answers are on page 4 -

http://johnlsayers.com/phpBB2/viewtopic.php?t=598

I'm kinda using this thread as a temporary "FAQ", til hell freezes over or I get time to write one :=)

Oh, and Ari's already an old friend, we've discussed lots of things including the difference in availability and cost of materials - Hey Ari, good to see you back... Steve

 

[RICK FITZPATRICK]

Wow! Wow! Wow! Steve, you've done it. Best stuff I've ever read. No more questions along these lines. You've covered it all at last. Man are you good.
And thanks for sharing all your hard won knowledge with everyone. You could make a fortune on a book. But being the gentleman you are, you have given the home studio builders the truth. For free.

Alright you guys. Pay attention. Its all said now. Any other people asking for this stuff can be directed to the truth on Steves forum. In fact, I'm making a permanent bookmark to Steves forum. We all owe Steve a dept of gratitude. I know he has spent a good part of 20 years or so collecting, sifting, asking, proving, and saving. Thanks Steve. Anything I can EVER do for you, please feel free to ask. That includes the shirt on my back ANYTIME. Well, I guess all there is to do now is......ah, have a cold beer and grin!!

fitZ


ps Steve. I tried to thank you at your forum, but the reply button kept takeing me to the index page

 

[knightfly]

Man, that's wierd - the index page? better check that out - BTW, glad you liked that link, I really AM gonna try to find time to sift it a bit, plus add more. Later... Steve

 

[bolehnggak]

Hi, thanks for all who participated in this discussion, Steve, Rick, everybody.

First of all, I do live in Indonesia.

Well, you might not expect to find something that you usually use for soundproofing here, for example, I can't find those Owens Corning 703s here. But sometimes you can find something that you wouldn't expect.

My question about MDFs here, and I'm actually hoping that I could use them, is because I can get them cheap. The price of the used-but-in-excellent-condition 12mm MDF is cheaper than a 9mm gypsum board.

The prices of building materials and building cost here are different from Australia, U.S, and European countries. Here, the cost of building brick wall is cheaper than a stud wall on a frame, and plywoods are expensive. So when I said that I use double brick wall construction for my studio, most people abroad are thinking that I'm very rich, but no, the cost of brick wall is very cheap here.

Thanks for all answers and help. But if there's more opinion, feel free.

Ari

 

[knightfly]

Ari, MDF comes in a few different weights now so I don't have exact mass, but generally 12 mm MDF would weigh about 25% more than 12 mm gypsum, so from a mass standpoint it would be quite good for sound walls and ceilings.

I would recommend you follow Ricks first post as much as possible though, especially about drilling and countersinking, and some kind of panel lifter. If you can't get one, you could make something makeshift with boards to help hold the panels while you fasten them. 12mm MDF weighs about 68 pounds per 4' x 8' sheet, so it won't be real easy to hold up.

Be sure to offset joints in both directions between layers, and seal everything. I hope you can find some proper acoustic caulking, the other regular stuff will degrade sound proofing in a fairly short time... Steve

 

[OzNimbus]

I went with a 5/8" drywall, 1/2" MDF, 5/8" drywall sandwich for the walls, but went with two layers of drywall for the ceilings. For the record, it worked out great.

-0z-

 

[RICK FITZPATRICK]

Hello Ari, I have a few more suggestions. Nothing is worse when working on these sort of problems than lifting the panel to the ceiling only to find that the room is not square, the joists are not parallel, your holes don't line up, etc etc. There are a few tips I have to offer, but first need some information from you. I agree with Steve as far as the mass is concerned. And CHEAP would end any other arguments for me

Soooo....if you would like some suggestions, please provide the following.

Room dimensions.
Joist nominal dimensions and material.
Joist spacing
Details of the construction of the ceiling framing. ie...blocking between joists?, at the perimeter?, etc. I want to see what your working with. Believe me. Planning is the real solution here. MDF can be a real pain in the ass to use as ceiling panels. The larger the area, the more you must be aware of. So, I've already written the suggestions, but before I post them, I want to know what the existing conditions are. Otherwise I am spitting in the wind Let me know if you need this or not so I don't make an ass out of myself. Ha! Having a background in architectural millwork allows me to foresee problems that you maynot be aware of, and I will share these with you to make things easier. If you so desire. Otherwise, I'll keep my big mouth shut.

fitZ

 

[bolehnggak]

The joists are made from 5x7cm wood, the spacing is 60x60cm.
The room dimension is hard to describe, because it's not rectangular. In fact, there is a picture in my previous posting, titled 'Acoustic Treatment for my Studio, need help'
I can't post the same picture twice to the list.

Ari