# Forum Home Renovation Plastering  whats the correct way to double layer plasterboard?

## sundancewfs

What is the correct way to double layer plaster board? Do you completely finish the first layer? or what stage do you finish it to? How do you attach the second layer? Do you offset any joints?  Can you put expansion joint caulking along to floor/wall junction to seal it? etc etc and whatever other things spring to mind from the proffesionals out there. I'm thinking of the sound abatement style installations mainly...party walls, toilet walls, theatre walls. Is there thicker plasterboard avail than 10mm. I know in the USA they have some very thick stuff.

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## seriph1

sound abatement is a huge issue in some places and I strongly recommend getting an appropriately qualified person to advise. Two layers of plaster, while better than one, may not address the issue depending on the frequency of the noise.  
If you are committed to placing two layers on your walls, I reckon there'd be little point doing any sort of finishing to the 1st layer, other than stopping up the joins. 
A friend of mine tried your idea without success but he lives on Bell Street Coburg which is among Melbourne busiest roads.  
Eventually he double-glazed the windows, added refrigeration panels to his rooms, placed rockwool batts in the roof space and sealed the bottom of his home (along the perimeter foundations) with refrigeration panels covered with cement sheet. 
All this made a considerable difference to the higher frequency noise but made no difference to the low frequency stuff, (truck rumbling) as it transmits through solids  -  of course, he only discovered this snippet after getting the noise (or whatever he was called) engineer in.

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## Rod Dyson

Stagger the joints (off set), No need to stop up 1st layer.  
13mm or 16mm PB is available, steer clear of the sound check plasterboard. Waste of money use 13mm or 16mm firecheck instead. Better rating and cheaper. 
If sound is really an issue consider using furing channel on resilient clips. 
For the best results you need to isolate the contact on the frame and plasterboard. The resilient clips do this.  
Another methed we use (if space is a problem), is getting 10mm thick strip rubber from Clark Rubber and cut into 30mm x 30mm x 10mm blocks then sheet the 1st layer then glue the blocks onto the face of the first layer where the fixings for the second layer will go, so the screws actually go through the rubber block. I would screw fix through blocks at each edge of the sheet and the middle. This 10mm cavity creates a great sound block and the rubber blocks minimize the sound transmission while maximising the size of the room.  
For sound proofing you need to consider these three things. 
Density (thickness and weight per 2 of the lining)
Isolation (rubber mounted clips and or double framing to prevent sound transmission)
Absorbtion (insulation to muffle and absorb the sound waves). 
None of these on there own will work! For the best results you need to have a combination of all three working for you. You will get a reduced result using two only. 
To get results using only two items you need to increase the rating of the prouducts used. Eg. use 2 x 16mm pb or even 3x 16mm if you cant isolate or insulate, rather than 2 x 13mm. 
Or use the densest insulation you can fit in the wall. 
Hope this makes sense, I hate seeing people wasting money on ineffective sound systems or being dissapointed in the results due to a lack of understanding of what can or can't be achieved.  
Each application is slightly different depending on ceiling and floor structure. You may have to sound proof these as well. 
To give you an idea of what is required to completly get rid of sound transmission, we designed and constructed a recording studio that had to be 100% sound proof between studios.  
The walls consisted of 3 frames the centre frame had 2 x 16mm plasterboard each side with acoustic insulation between. Then the outer frames both had 3 layers of 16mm plasterboard each side with acoustic insulation beween. The floor also had multi layers of framing and 16mm plasterboard with flooring over the top. Then a layer of rubber and carpet over. Like wise the ceiling. All entry doors had an air lock.  
I am relating this story so you have an idea of what is required to completely block sound. 
Cinema walls we have done consisted of 2 x 150mm frames side by side (but not conected), with the cavity completely filled with acoustic insulation and 4 layers each side of 16mm plasterboard.  
Compare the ratings of different plasterboard types here http://www.how2plaster.com/sound/compare.html 
A bit more about sound proofing here http://www.how2plaster.com/soundpr.html 
I hope this helps. 
Cheers Rod 
BTW there is a 20mm thick shaftwall pannel for sound/fire rating between units different application again.

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## sundancewfs

An excellent reply Rod, thankyou. and seriph1, thanks for the real world experience story. 
Food for thought..... yet again   :Smilie:

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## Dave_KB

If sound is your issue then you might want to have a look at this website:  http://www.johnlsayers.com/phpBB2/index.php 
It deals with recording studio design and building but there's lots of info about installing plasterboard.

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