Bricks, Blocks and Gypsum

Greetings studio people . . After several interesting weeks of reading and researching this forum, its time to take the plunge with my first post! While I still have many decisions to make and sketches to do before I can present my proposed layout / floor-plan, I feel the need to post a few preliminary questions that will help 'shape' my final thinking and approach. I've done my best to get the answers on previous posts so please bear with me if I missed something :roll: I will be dividing up a large ground floor space to create the studio rooms. The area has a solid floor slab with a live load rating of min 250kg/m2 and a ceiling slab 200mm thick. The distance between slabs is 3770mm. Question time . . In South Africa building with brick or block can cost up to 50% less than utilising a two skin 15mm gypum/ stud construction (when done properly) and I am thus considering my options in this regard. My concerns are about performance in terms of TL and more specifically what type of brick / block will perform better in terms of isolation . I have whittled my brick choices down to: Clay brick walls using (218x106x72mm - 3.6kg per brick) or Hollow cement block 7mpa filled with sand (390x190x190mm - 16 kg each block -unfilled weight) Any suggestions on what may be the better type to use? In both instances I will be using a double wall construction with air gap / fibreglass isolation and plastering the walls. As the clay brick will utilise less physical space, that would be preferable choice . . Should the slab not be able to with stand the loading of a double brick wall I may need to consider a single brick wall and single gypsum wall combination - anything I should be concern about using this method?? Is there any special technique or product to be used for placing the blocks on to the slab? Lastly, will a brick wall (as opposed to a gyspum wall) in the control room present any specific challenges, issues or additional requirements in terms of acoustic treatments? (OK thats 5 questions ! :oops: ) Really appreciate the sharing of ideas and experiences on this as I move forward . . Thanks Matt

isol8 wrote:

Should the slab not be able to with stand the loading of a double brick wall I may need to consider a single brick wall and single gypsum wall combination - anything I should be concern about using this method??

I think a double wythe brick wall registers at 50+/- on the STC scale and has very good isolation due to the mass as it registers in the TL region. In respect to the slab this would have to be certified, the points of load concentration of the brick load would require a footer, width and depth depending on dead load and geographical region.

isol8 wrote:

Lastly, will a brick wall (as opposed to a gyspum wall) in the control room present any specific challenges, issues or additional requirements in terms of acoustic treatments?

Yes. A brick finish is a hard boundary, harder than sheetrock. But still will require tuning in respect to the properties of the room.

Thanks Brien for taking the time to respond It would still be useful if anyone out there knows if you get better isolation from solid clay bricks or sand filled concrete blocks? The STC chart at http://johnlsayers.com/Recmanual/Pages/STC%20Chart.htm mentions hollow core blocks (STC 48) but not ones filled with sand. However it appears from the chart that blocks would be better that than rendered solid clay bricks (STC 45). The chart does not give values for any double brick/block insulated walls so its hard to get the comparison to double stud gypsum which has been rated at STC 59. I will be using a structural engineer to certify the slab loading once I make the choice of wall construction to follow. The point I was getting to in terms of brick walls in the CR was if such a hard surface requires generally more acoustic treatment or a different approach than a room with gypsum walls ( a generalisation I know!) Matt

It seems to me that you are asking questions related to mass law. You'd need to determine the surface density of each proposed wall, and the use the equations of mass law to predict the expeted isolation. It changes with frequency, of course. You can approximate transmission loss using these equations. Imperial: TL = 20 log (Ms x f) – 34 dB where: Ms = Surface density (mass per unit area) in lb/ft2 F = Frequency OR Metric: TL = 20 log (mf) - 47 dB where: m = surface density (mass per unit area) in kg/m2 f = frequency (Hz), Not sure if anyone mentioned this yet, but STC is a lousy way of deciding on isolation for a studio, since it does not say anything at all about low frequencies, which is where your biggest problems will be. You should be using TL, not STC, to compare isolation capability for studio walls. - Stuart -

Soundman2020 wrote:

Not sure if anyone mentioned this yet, but STC is a lousy way of deciding on isolation for a studio, since it does not say anything at all about low frequencies, which is where your biggest problems will be. You should be using TL, not STC, to compare isolation capability for studio walls. - Stuart -

The only post that mentioned sound transmission class was mine. The op used the term TL.

The only post that mentioned sound transmission class was mine. The op used the term TL.

My bad! Sorry! :oops: That's what I get for not read back a few posts to make sure... :( - Stuart -

" solid clay bricks or sand filled concrete blocks? " Overall you want a lot of mass that is flexible. This is why mass loaded vinyl (MLV) has risen over the years as a "goto" material. It has mass and it has flexibility (limp membrane). But the truth is, mlv is very costly and does not perform well to "justify" the cost. It is after all a material designed to reduce noise in a construction area, which it does well, but if it is morphed (if you will) into a tuned system as we deal with here, it has not only not been tested, it meets with a different standard. That standard being that we frame walls and install sheetrock according to known specifications based on specific materials, dimensions, etc. That said, a flexible panel is better than a rigid panel so a solid mortar joined brick assembly of any kind versus a hollow block filled with the flexible mass that sand will yield is the better option...hands down. Even if the hollow block are the same dimensions as the brick in question, the sand (flexible and mass) trump a brick wall that is known to have rigid paths (short circuit) due to the mortar droppings in the cavities. "It would still be useful if anyone out there knows if you get better isolation from solid clay bricks or sand filled concrete blocks? " And now you know the rest of the story.

HI Stuart Thanks for the formulae - I'll get the calculator out and look at this more scientifically :idea: . . Any ideas on how a double brick wall with fibreglass insulated cavity impacts on the formula / calculation of total TL as opposed to a single wall? Briens post indicates that isolation is positively impacted by the flexible mass of sand in hollow blocks. This leads me to believe that its the type of mass and not just the total mass that is important in the calculation and thus may determine the actual results? While the potential performance of brick / block wall systems seem to be impressive, its interesting to note that most discussions centre around gypsum as preferred solutions :?: the learning curve continues...

"Briens post indicates that isolation is positively impacted by the flexible mass of sand in hollow blocks." It is more the block and sand VERSUS the brick and mortar which is a rigid panel. If it is a veneer then it [the brick] is attached to the structure with brick ties, a coupling or short circuit, what I call a coupled assembly. Others over the years have referred to this as a three leaf, which is incorrect due to the short circuit. It is simply a coupled assembly. If it is double wythe brick wall then the potential for short circuit exists simply due to the always present potential to the craftsman not understanding what a "bridge" or "short circuit" is and why you have to clean up every layer of brick laid inside and out. This is a difficult task simply because it requires, for an acoustical environment, an airspace large enough to get a small mans hand down into the cavity to keep the mortar from building up at the foundation level "This leads me to believe that its the type of mass and not just the total mass that is important in the calculation and thus may determine the actual results?" Mass is mass. What matters most is how it is installed and how careful the materials are joined and exactly what mass is being considered. The reason gypsum is used in most of the dialog found here is that it has supporting data...that is the only reason. Like take lead sheeting for instance. Lead is better than anything. but you and I cannot afford it. If we can afford it we most likely cannot pay for the structure that can support it. So we think about concrete as an alternative which it does well but at a cost and space consideration for the project. Not the same thing, but clearly the better alternative when lead is first considered for a project.