[Strawbale]Re: Some loadbearing compression ideas/questions

Mark Bigland-Pritchard // Low Energy Design hyphen at dial....com
Wed May 4 22:49:37 CEST 2005

I finally got round to reading parts of the Danish report on health and 
safety issues in sb building the other day (as well as some British 
material on farming and respiratory diseases).  It seems that dust and 
spores are potentially a problem in an enclosed space - the Rijven dip 
seems like a good procedure for this reason as well as the others mentioned.
As regards dipping and compression, the rational way forward (where the 
design permits it) seems to me to be to dip, build the wall quickly and 
precompress before the mud has a chance to fully set.  There may still 
be some cracks, but they can be easily dealt with in putting on the next 
plaster layer.

Rene Dalmeijer wrote:

> Riki,
> You should think more often you come up with very good questions some 
> of which I cannot answer for myself. I will venture to answer your 
> questions to hopefully start a debate.
> On Apr 28, 2005, at 07:36, strawbale-request at amper....muni.cz wrote:
>> Some thoughts about compression for you tecnical people.  I have been
>> thinking about these techiniques that are popping up as ways to reduce
>> compression on loadbearing walls.  Specifically the techniques like 
>> those
>> used by Tom Rijven, or the man in ávila:  they use clay paster on the 
>> walls
>> before or during the wall-raising.
> I am a strong supporter of Tom Rijven's 'French dip' for some of the 
> same reasons you mention but also because of instant fire and weather 
> protection. It is also a very good way to make substandard (low 
> densitity) bales more buildable, they become more stable.
> <snipped>
>> etc.  SOunds good, huh?  But the other day I was thinking (I do that 
>> once in
>> a while) and I thought to question:  A compressed wall is sure to be
>> stronger, no?  it may be more comfortable avoiding compression, but 
>> will it
>> not make the walls weaker and capable of bearing less weight?
> It depends Pre compressing does not really make the walls stronger it 
> just lessens the amount of creep (long term settling under load) High 
> density bales are definitly stronger. They exhibit a higher E-modulas 
> of elasticity which realy means that for the same load they deform 
> less then low density bales.
>> On my
>> load-bearing walls I have a clay-tile roof, I don´t know if I could
>> recommend putting a heavy roof on an "uncompressed" loadbearing wall . .
>> .But in the testing people have done they say that the plaster bears 
>> more
>> weight than the bales themselves, some maybe my doubts are irrelevant 
>> . .
>> .What do you all think?
> The plaster always ends up carrying most of the load it is simply much 
> stiffer then the bales. Not precompressing means the walls will creep 
> (settle) much more over time then without precompression. 
> Pre-compression means you can build faster. I would aways go for 
> precompressing. It is not such a bother I find and helps making the 
> walls easier to finish because they are more stable. There is also 
> much less changce of plaster cracking. With a tile roof I would always 
> pre compress 4% of the total wall height as found out by John Zang. 
> (based on un-French dipped bales) We should do new tests with dipped 
> bales.
> Rene
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