MDF/Plasterboard combination walls

[Deluks]

I've just bought a load of cheap (ish) 18mm MDF, and have enough to build my proposed studio twice. I was gonna go with 4 layers of plasterboard, 2 on inner leaf & 2 on outer leaf but now I've thrown MDF into the mix, I need to know the best way to use it.

So I've got 2 layers MDF and 2 layers of plasterboard to work with, do I go..

2 plasterboard on inner leaf, 2 MDF on outer leaf?

2 MDF on inner leaf, 2 plasterboard on outer leaf?

or another combination?

I was thinking, from the inside of the room:


Plasterboard>MDF>Rockwool>Plasterboard>MDF

>Outside world (actually the inside of the garage)

Reason being that plasterboard will look nicer on the inside and mdf will be tougher on the outside, against day to day general garage use.

I'd added a crap not-to-scale pic below. Walls A & B will be built against existing concrete wall, so will be single stud, walls C & D will be the double leafs I'm referring to. The yellow stuff is rockwool

 

[knightfly]

You'll get better isolation from your walls if you use dissimilar materials in each leaf; so it would work better if one side of the frame has MDF (2 layers) and the other side of the wall has the gypsum... Steve

 

[RICK FITZPATRICK]

Steve is ALWAYS concerned with results. But I question the use of MDF on walls if code calls for a fire rating that drywall meets. I don't know about the fire rating of MDF though. Steve?........ Maybe sandwich it between 2 layers of drywall on each leaf....man, what a leaf that would make. Reminds me of someone at Studiotips.......used SEVEN LAYERS of drywall!!! Man, his wife must...... well lets just say, influences him
fitZ

 

[RICK FITZPATRICK]

Oops, just noticed this is in a garage. That may make a difference, I don't know.
You will also get more isolation like this....

 

[Deluks]

Thanks for the advice guys, I've just worked out that I've just enough to do walls C & D 3 times over, so I'm gonna put 2 mdf's on the outer, one on the inner, and finished with a single sheet of plasterboard.

For walls A & B I'll use 2x mdf and 1 plasterboard all at once, as I'm not to sure how soundproof those concrete blocks will be.

I don't think fire regs will be a problem, as the garage is detached from the house, approx 80ft away at the end of the garden. My dad also used to be a fireman, so he'd notice if anything seemed dodgy.

The 7 layer guy was Paul Woodlock, a legend amongst DIY'ers like myself. He intends to use his studio in the early hours of the morning, quite quite mad!

The biggest challenge facing me will be getting the ceiling as good as the walls. There are welded metal braces holding up asbestos type sheeting. They won't be able to take any weight, so I'll have to build around them. Also they are only 7ft at their lowest point.

More pics below, any suggestions?

 

[Deluks]

Oops, just noticed this is in a garage. That may make a difference, I don't know.
You will also get more isolation like this....

Pretty much the way I'm going to go.
As you can see in the pics, the walls are concrete blocks about an inch and a half thick. They can't be moved or replaced. Is there anything I can do to increase their performance, like a simple plastering job? or painting them with some sort of coating?

Another issue is that the double walls (C&D) will be staggered but sharing the same top and baseplate, probably a 2x6. I'm on a budget, both space and cashwise, so I don't think there's any real alternative.
The ceiling is still looking like being the weak spot. The second leaf there will be thin roofing sheets, not looking too good

 

[knightfly]

If A and B are HOLLOW concrete block, you're looking at about STC 45 as is; there are a couple of values for this here, near the bottom -

http://www.saecollege.de/reference_material/pages/STC Chart.htm

You can up your isolation on those a few dB with a 1/2" rendering job, but not a lot; probably only another 3-4 dB or so. If your budget were greater and you were a masochist, I'd suggest FILLING the blocks to the top with sand, making that wall a single leaf instead of a double; then, you could furr out (not touching the wall) with 2x4's and a couple layers of gypsum.

However, there's little point in all that if your ceiling is gonna screw you; and from the look of it, that's the case. The asbestos corrugated probably doesn't seal worth a hoot, and those wide spaced steel "wanna-be" trusses scare me too;

If you put an inner ceiling to go along with your inner walls, and keep each leaf of mass continuous around the room, that would give good iso; but to do that on your ceiling would require at least 2 layers of gyp board each side of 2x6 joists on 16" centers; 2x4's, even on 12" centers, wouldn't span your 10 foot dimension safely with enough mass to help.

Using 2x6's, your ceiling height would be lowered even further; subtract about 8" from existing height.

Not an easy one... Steve

 

[Deluks]

If you put an inner ceiling to go along with your inner walls,

So you think it would be decent soundproofing if I put 2 ceilings in, even though there's the existing roof creating a controversial '3rd leaf' ??

I can put beams up either side of those braces which hang down below them a tiny amount, and build the ceiling between them, finishing off with a couple sheets of plasterboardwhich are fixed to the wood but beneath the brackets, only losing about 2" ceiling, which I can live with.

The only prob then would be the small gaps where the brackets 'cut-in' to the ceiling area. Now if I could find something flexible and dense to fill that void....

Do they sell acoustic sealant in 5 gallon drums


Moral of the story: American's aren't perfect but at least they know how to build a garage! Some of the ones I've seen are better than my house!

 

[knightfly]

Must be our obsession with CARS that cost more than BOTH our houses... :=)

Is that corrugated asbestos stuff very thick, or just a few mm like other corrugated materials?

Of course it will cause a third leaf weakness, but short of removing the roof and replacing it with something that works, about all you can do is try to compensate in other ways.

The way I was thinking about would be to have new ceiling joists (possibly fit between the "un-trusses") but with two layers of gypsum on TOP of the new joists and 2 more layers BENEATH the joists - this in itself would comprise a 2-leaf barrier, and yes the asbestos would weaken that at some frequency relative to the mass of the asbestos and the average air gap, etc...

Another problem is that if this is REALLY asbestos, you do NOT want to disturb it in any way, other than spraying it with heavy paint to contain the fibers... Steve

OTOH, if you can SEAL that asbestos roofing, and maybe thicken it with heavy undercoating material, you might come closer to nirvana by just putting your 2x6 joists between the "un-trusses" as you mentioned, and fastening THREE layers of gypsum UNDER the joists, first filling the gap between the asbestos and the gypsum COMPLETELY with spun fiberglass insulation; this would, at least, make up a m-a-m partition - with a 8" air gap filled with insulation, you would be looking at (wild-assed guess here) about STC 50-56, depending on coupling, etc - this was calculated with approx. 3mm (0.120") asbestos, 8" air space with insulation, and 3 layers of 5/8 gypsum (15mm each), and of course assumes total hermetic seals at all joints. Your low frequency TL would be around 26 dB, which means people outside would start to hear LF stuff at around 84-85 dB, and mids/highs a bit louder than that...

Thinner asbestos would hurt things a bit, but not too bad; 2mm lowers it to around 50-53 dB STC with almost NO change at mids and highs...

 

[RICK FITZPATRICK]

The 7 layer guy was Paul Woodlock, a legend amongst DIY'ers like myself. He intends to use his studio in the early hours of the morning, quite quite mad!

Hello Deluks. Hmmmm. If you are familiar with Pauls project, you must also be familiar with Studiotips. Out of curiosity, with a resource such as that available, as well as Knightflys forum here...
http://www.johnlsayers.com/phpBB2/viewforum.php?f=2&sid=f8f186822f24bb012e5d73978154c7ca

I am curious why you asked here? There are far more scientific acoustical solutions found there, wouldn't you think? Just curious though.
fitZ

 

[Deluks]

Is that corrugated asbestos stuff very thick, or just a few mm like other corrugated materials?

Only a few mils, they are quite heavy sheets though, I don't think it's dangerous until you start breaking it up.

The way I was thinking about would be to have new ceiling joists (possibly fit between the "un-trusses") but with two layers of gypsum on TOP of the new joists and 2 more layers BENEATH the joists -

The problem is that the layers on TOP, would be intercepted by the trusses, they would prevent wall-to-wall coverage

OTOH, if you can SEAL that asbestos roofing, and maybe thicken it with heavy undercoating material, you might come closer to nirvana by just putting your 2x6 joists between the "un-trusses" as you mentioned, and fastening THREE layers of gypsum UNDER the joists, first filling the gap between the asbestos and the gypsum COMPLETELY with spun fiberglass insulation; this would, at least, make up a m-a-m partition

This is probably the only real option, but the way I was thinking would be to put the layers (two 18mm MDF and one 12mm plasterboard) on top of the beams, except where they meet the trusses and pass them underneath instead. See the attached (cross section) pic to see what I mean.

This would lessen the m-a-m airgap between the metal trusses, but I really need that height to stop the room from feeling too cramped. Plus I could hang some bass traps from the ceiling in those gaps which would be pretty much essential given the small size of the room.
When you say 'spun fiberglass' do you mean the big rolls of standard roof insulation? I was gonna use rockwool slabs in the roof cavity but if you think this stuff would be better?
It would also work out much cheaper than rockwool slabs, and my local DIY store runs a "3 for 2" on the 170mm thick rolls, they call it 'glass mineral wool'

Getting there....(I hope)

Del

 

[knightfly]

The main downside of that plan as you mentioned is the reduced air gap; with that light an outer leaf (the asbestos) you need all the air space you can get for decent isolation.

If isolation isn't that important, then what you drew should work OK; but the other downside is all those 90 degree corners where the ceiling height changes. Each of these will HAVE to be absorbed, or each 90 degree inside corner will reflect all mid/high frequency sound right back to the source in parallel rays.

That's about it AFAIK... Steve