[Strawbale]Re: Rendering the outside only
rene.dalmeijer at hetnet...
Wed May 25 10:52:52 CEST 2005
Not rendering the inside surfaces would obviously allow for much higher
levels of high frequency absorption. I am not sure about low
frequencies though. I am almost sure these would be lower then when
plastered with an earth plaster. We have been doing SB sound insulation
testing here in an acoustic test chamber. a normal SB wall with earth
plasters achieves roughly 55 dBA. The level of attenuation varies over
the spectrum Low frequencies are attenuated much less ie roughly 30 dB
at 63 Hz. For recording purposes this is maybe just enough to prevent
unwanted background rumble getting into the recording. I expect that
not plastering the inside surfaces would seriously decrease the
attenuation at 63Hz maybe to levels below 25dB.
To absorb or attenuate sound at low frequencies you need mass. This
means the internal plaster is quite an important contribution to the
amount of low frequency absorption.
Besides the acoustic considerations I always strongly advise to plaster
all exposed straw bale surfaces for the following reasons:
a) Fire, pest, rot prevention.
b) Structural as the building is load bearing I expect that the walls
will start to bow outwards due to the uneven load distribution on the
bales. The plaster on the outer surfaces is much stiffer ie will carry
most of the loads The inner surface is not as stiff and will deform
more over time as the bales settle.
c) Due to the almost certain risk of moisture problems developing (due
to not plastering the inner surfaces) could lead to a health risc as
spores are free to move into the inner space.
On May 25, 2005, at 07:36, strawbale-request at amper....muni.cz wrote:
> I've been helping a musician build a strawbale recording studio (the
> 'Strawdio'). It
> is a simple, one storey, load bearing structure - four walls and,
> soon, a green
> He has been wondering about the possibility of leaving the inside
> surface of the
> bales bare. This would be accoustically superior to a rendered or
> surface, and would be ideal for it's intended use. But I wonder if
> anyone would
> like to comment about the implications of doing this - structurally,
> thermally, or in
> any other way?
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