MDF or Caneite (Homasote) in the Sandwich?

Faderus · Post by **Faderus** » Thu Jul 10, 2003 9:15 am

Hi All,
Hoping to start construction garage studio in a few weeks in existing aged but waterproof ‘fibro’ shell on solid concrete, approx 6.5 x 8 meters, headroom 2.4 m concrete to rafters. (may not fill entire shell with studio and control room as budget may not allow but shooting for that)…am starting to cost materials in detail now. Sound insulation crucial as medium loud rock band will be inside, neighbours a backyard’s length away outside. Will not internally line shell as constantly need to check old structure for White Ants ( Oz Termites) and other decay…so will be leaving 0.5m ‘walkway’ round outer edge of internal studio. Am planning to follow John’s construction plans on SAE pages incl. floating double ‘yellowtongue’ chipboard floor, double walls each with 10 and 13mm Soundcheck 'Gyprock' Plasterboard and MDF sandwiched between on both sides. (The CSR _16_mm plasterboard is ‘Fyrcheck’ these days, so assumed the slightly thinner Soundcheck would be better). Semi rigid batts in gap (Insulco or CSR Soundscreen). Ceiling….arrrgh! I’ll get there. One little question (OK there’s a million spinning round in my head, but here’s my tentative first one

: Read somewhere…maybe this site, not sure, that ‘Caneite’ (in US Homasote?) may be better than MDF in between the 2 layers plasterboard. Any thoughts? Or MDF one wall, Canetite other? Many thanks.. Glad to know you’re all out there.
F. (hoping he hasn’t ‘bitten off more than he can chew’).

knightfly · Post by **knightfly** » Fri Jul 11, 2003 12:47 am

F, the dissimilar approach should get you better isolation, since it would make each "leaf" of the wall have a different resonant frequency. The resonant freq. is what gets through the wall, so having each half of the wall different tends to keep any one freq. from going through.

If your outer shell is tight, the best sound proofing will be had by having only one other "leaf" in the wall, the one on your new inner frame. With that much air between leaves, you should get really good isolation. If possible, you should add another layer to the inside of the outside wall, without leaving any air space.

I'd put up the inner frames, put at least two and possibly three layers of wallboard on the OUTSIDE of the inner frame (where your ant patrol area is), and use the inner stud cavities to build John's "inside out" walls - this gives you a large air space between two heavy masses, which is nearly impossible to beat for less than 5 times the price. Then, you will already have some good absorption inside (built into the wall) without having to build separate units.

Your most efficient use of materials is a double leaf partition with ONE air space, preferably filled with insulation. This is true of ceilings and floors, as well as walls... Steve

Faderus · Post by **Faderus** » Fri Jul 11, 2003 7:53 am

Steve...wow...is this what they call 'lateral thinking'? Never occured to me to use outside wall as part of acoustic structure as just made of thin 'fibro' asbestos (cough) strengthened cement sheet. But I can indeed add the layer to it, and I'll do as you suggest.
Very many thanks,
Faderus

knightfly · Post by **knightfly** » Fri Jul 11, 2003 11:26 am

F, just in case I'm missing something (not familiar with all types of construction in some parts of the world) your goal, for the most effective sound proofing, is two, and ONLY two, centers of mass (the more, the better) separated by ONE, and ONLY one air space (preferably with some type of insulation somewhere in the gap) - the wider the air gap, the better (your "walk-around" space is GREAT) -

If this "fibro" stuff is attached to a frame, you could conceivably insert extra layers of wallboard between the frame members, snugging them up against the outer layer and caulking them tight with ACOUSTIC-rated caulk, in order to "beef up" that center of mass.

The inner wall (only one side of frame should have paneling) should be at least two layers of board, like 5/8"/16mm gysum wallboard, and a DIFFERENT, absorbent material (such as Homosote) between the two usually helps isolation if you can do it.

If you put the paneling on the INSIDE of your inner frame, you should fill the stud cavities with either 60 kg rockwool/mineral wool, or Knauf rigid fiberglas of the same density; this filling can be placed right up against the wallboard to dampen the wall vibrations, which will improve Transmission Loss through the wall.

Find a local source of real ACOUSTIC rated caulk, and hermetically seal EVERYTHING as you go - the smallest crack will downgrade your walls by several dB. The acoustic-rated caulk is designed to stay flexible and soft, but with extra body for best sealing of cracks/gaps. The best places to find acoustic caulk are commercial insulation/drywall companies - if you have no luck there, I have a link to a web source - it's more expensive (nearly double) but better than losing a serious amount of sound proofing in a few months or so, due to the wrong caulking. Especially since a lot of things you will caulk can't be gotten to once they're finished.

On the possibility that your existing "fibro" stuff is nowhere NEAR hermetically sealed (cracks, holes, etc) you could either put a layer of stucco (or other) over the outside to seal it, or put a double layer of wallboard on the INSIDE of the OUTER frame (the one the "fibro" is on) and LEAVE the outer "fibro" layer as it is, so it doesn't make the wall into a "triple leaf" wall. (Remember, you want ONLY two layers of mass with only ONE air space sealed between them, so any additional "leaves" should have air circulation to the outside.

I hope that didn't confuse the issue too much - if I prompted more questions please don't hesitate to ask them... Steve

Faderus · Post by **Faderus** » Fri Jul 11, 2003 7:03 pm

Steve,
Thanks again for taking the trouble to reply in such detail…I really appreciate it and it’s a great psychological boost to know that an expert is considering my problem! Although I did understand you to be telling me to put wallboard _between_ outer structure frame members, I had nagging doubts that I hadn’t got the message. I now understand perfectly re: 2 x centers of mass, 1 x airspace. ‘Fibro’ is indeed nailed on the outside of a conventional wooden frame. When I removed the crude Masonite-type lining from all walls (building had been used as teen/granny flat by previous owners), I found the now exposed frame timber had considerable termite damage, although not active…someone must have eradicated them a while ago. This will necessitate my replacing structural members in several places, but easy enough. My concern was that the creatures might attack again, although I’m digging trench around building so soil not in contact with bottom timber as was before. Thus I was reluctant to put internal lining on again, and hence the ‘ant-patrol’ strip.
The fibro is in very poor condition, with cracks and holes…far from hermetically-sealed, and bits of daylight visible all over the place. I considered replacing it all, maybe I should, but I am already replacing about 50% roof area with new corrugated ‘zincalume’ metal sheets, and if I put up the budget again, my wife might disown me!
However, if that would be the best way to go, so be it. Stucco good idea, but fibro so old (at a guess 45 yrs), might not be worth it. Was planning to just replace the obvious cracked or missing bits, but even when done, although building (amazingly) keeps water out, is and would still be as airtight as a sieve.
After reading your first reply, was hoping that putting wallboard between frame cavities would seal it despite leaky ‘skin’, if caulked sufficiently. Was planning to possibly wrap this wallboard in polythene sheeting in case fibro ‘sweats’ water through into it. But maybe caulk wouldn’t stick to the polythene. Since outer fibro skin really is so un-airtight, perhaps wallboard on inside of frame? (and presumably either way, under rafters too. .all caulked together). I am very keen now on making this outer wall part of the acoustic structure, so that I can utilise ‘walk-around space’. (Even if I in fact loose the ‘ant-checking capability’ due to wallboard lining…what the heck.. I’ll just get a Pest Guy in).
I hope I’m not myself becoming a Pest Guy with this long post

BTW there is actually about 50% more building area available but with reduced roof height, which I believe I could raise if necessary. Just mentioning this in passing.
Thank you again for the advice on caulk. I’m feeling guilty

Although I’ve read how important the proper stuff is, I confess - I was going to try and get away with cheaper Silicon caulk. I feel suitably chastened and I’ll make all enquiries to get proper stuff in Sydney now, and will definitely use the proper stuff! Also appreciate the Rockwool specs.
Steve, once again, I can’t thank you enough, for your time and expertise. Hope my long and rambling reply doesn’t a) put you or Forum readers into a coma b) bring server to its knees!
F.

knightfly · Post by **knightfly** » Sat Jul 12, 2003 3:30 am

Ben, you wouldn't worry about being long-winded if you'd read some of my posts :=)

I'm not enthused about your putting wallboard (at least not the kind I'm used to here in USA) up against a leaky outer covering, even WITH a vapor barrier in place - the very LEAST I'd recommend there would be the "Wet area rated" stuff that's used around bathtubs and showers, and even then I'd slap a heavy coat of tar-based adhesive on the "fibro" before sticking the wallboard to it. You need to be careful here in order to keep from getting a perpetually wet space, as well as NOT generating another air space between layers in this outer mass. That will weaken the isolation factor.

As to "get away with cheaper Silicon caulk" - at least in my neck of the woods, that's a myth. Even if you have to buy the right stuff online, the $7.50 a tube price equates to $2.50 a tube for the NORMAL size, 10 oz. tubes - the $7.50 online stuff is a 29 oz tube, and if you can find it locally you'll pay about $4 USD, which makes it about the same as $1.39 a tube for the regular size.

You'll need one of the "quart-size" caulk guns, they're about $15 at home builder stores. If they don't have them, I have a couple of online sources for that also.

If you don't want to mess with putting stuff up against the "fibro", you could put a vapor barrier inside and two or three layers of wallboard on the inside of the studs, then do your inner walls the same. You should end up with about the same isolation either way... Steve

Faderus · Post by **Faderus** » Sat Jul 12, 2003 9:08 am

Steve,
Glad my verbose style not a prob! Yup, point taken absolutely.
Will leave outer skin as is, ie not airtight, and put wallboard on inside of studs.
Have found that CSR, from whom I'm buying the 'gyprock' wallboard, make a caulk called 'Fire Mastic' which is allegedly an acoustic as well as fire-rated sealant. Their www site although doesn't say much more...but is is available in 'sausages' for which you purchase a 'sausage gun' which all sounds rather cool!
Is the product you use 'Quiet Zone'? I would appreciate your links, although if I have to import from US, might be expensive.
But again, I'll do whatever is needed. Not backing out now.
Again thanks for your ongoing help & support,
Faderus Pengiles Quadrant.

knightfly · Post by **knightfly** » Sat Jul 12, 2003 9:02 pm

F, Before you order stuff from the US, John will be back in a few days and may have some Oz sources for acoustic caulk, etc - if not, here's a few links -

http://www.osisealants.com/proseries/PS ... /sc175.htm

http://www.builderschoice.ca/caulk.htm

(you want the quart size gun for the large tubes of caulk.)

http://www.doityourself.com/store/0511931.htm

http://www.acousticalsolutions.com/prod ... /caulk.asp

http://www.usg.com/Product_Index/_produ ... eenLink=10

Not all these links are for sales, some you would need to contact for sales info. If you can find the right acoustic caulk locally, it should be around $4 US per quart tube, whatever that translates to in Oz$ (around $6???)

Sorry I confused you in my last post with another poster - sometimes things kind of run together... Steve

giles117 · Post by **giles117** » Sat Jul 12, 2003 10:26 pm

Hey Steve,

what do you think of OSI's SC 170?

http://www.osisealants.com/proseries/PS ... /sc170.htm

Bryan Giles

Faderus · Post by **Faderus** » Sat Jul 12, 2003 10:30 pm

Steve,
Very much appreciated.
I'll see if any of these brands retail in Oz first.
No probs re name confusion, understood. In fact I'm liable to forget my own nick soon and start using my (gasp) real name

In any case, I'm not buying anything for approx 3 weeks..when d.v. my funding will arrive for construction materials, and all the gear to go inside! It will be like, as they say here in Oz "all me birthdays have come at once!"
F.

knightfly · Post by **knightfly** » Sun Jul 13, 2003 4:59 am

Hi, Bryan - I haven't tried it yet - at this point, a lot of my advice is coming from two places - what I've done that DID NOT work, and the resultant studies (spare time over the last 20 years) to correct that the next time around.

I'm still gathering ideas/products/sources for my next venture, which is a 2200 sf facility (16 foot ceilings minimum) with capability for 5.1, foley, voiceover, etc - I'm located about 100 miles from anything very professional, out in the countryside of Oregon (couldn't stand California so left the Bay Area and Video Maint. business in late 70's, brought my kids here so they could grow up with horses instead of "horse", got into recording audio with 1/2" 8-track, it got away from me, yada yada...)

The new facility is going to have at least 10" concrete outer walls, sound lock doors, and a "tunable" tracking room about 25 x 37 x 16', and should "break ground" within two years. By that time, my "ducks" will be SO "In a row" they'll be goose-stepping... :=)

Anyway, sorry to digress, but every once in a while I like to remind people of the limitations of my advice rather than mislead.

Have YOU tried the solvent-based OSI stuff? I like the idea of the "no freeze" thing rather than the "freeze-thaw OK" thing, although in my case, as mild as the weather is here I doubt the inside of my "bunker" will ever drop below 55 degrees even if I were to leave the HVAC turned off.

So far, what I'm finding as far as material supplies, is that anything more specific than plain old sheet rock and 2x4's is a real bitch to nail down locally. For example, my local Home Depot hadn't even HEARD of USG's RC-1 and claimed they couldn't even FIND it, much less get me some - their "wall of caulk" had the right gun but NOTHING even close to the "right stuff" for acoustic rated caulk, and I've yet to get time to check out local insulation/drywall places for availability.

I've yet to have my "BS filter" go into alarm mode when reading your posts on different BBS's, so I welcome your comments/advice, especially those from practical experience... Steve

giles117 · Post by **giles117** » Sun Jul 13, 2003 10:05 am

As soon as OSI calls me monday, I will place an order for the 170. (one tube) and 10 tubes 175 (depending on price, but I will pick their brians for the difference between the two products, so I'll let yah know.

Would've been nice if they wer eopen today, I had to run up to Ohio today for a show that was 1 hour from their offices.

Yah dig.

Bryan

knightfly · Post by **knightfly** » Sun Jul 13, 2003 4:32 pm

Great, Bryan - If they sell direct, I'd like to add them as a source in the materials forum - looking forward to your findings... Steve