[Strawbale] Mor(e) on sawdust floors (was Re: magnesite gung-ho)

[Rob Tom]

On Wed, 10 Jan 2007 18:12:48 -0500, Gene Smith <justsomeguync at yahoo.com>  
wrote:

>  I didn't go to every site, so maybe I missed one showing weathered  
> magnesite.

>>  The old  magnesite decks seemed to weather pretty bad,
>> which may mean that this  flooring option requires moderate
>> maintenance.

I haven't looked at any of the photos or websites yet mostly because I  
have no interest in doing "ChinaCrete" and I have no interest in it  
because:
(a) we don't have magnesium oxide readily available here at the local Home  
Hardware lumber yard in Carp, Ontario Canada and
(b) I couldn't even tell you where the nearest magnesite mine is and
(c) there are no salty seas nearby (other than the prehistoric seas that  
are about 1200 ft down underneath the granite bedrock )from which I could  
precipitate the magnesite.

But... I can tell you that Durisol makes a mineralised wood fibre product  
that is used for highway sound barriers. (ie The material is exposed to  
weather.) It is the same material that Durisol uses for their  
stay-in-place insulated concrete forms (ICF). The barriers here in Ottawa  
that I've seen have been in service for at least a decade and don't show  
any signs of deterioration... yet. Again, I'm assuming that the  
proprietary process that Durisol uses to mineralise the wood fibres  
involves MgO, an assumption that may be wrong... but I'd almost be willing  
to bet that it's not (wrong).

That being said, even Portland cement concrete can show signs of  
deterioration in as little as two or three years in some conditions and in  
some cases can be so bad as to require complete demolition and replacement  
in 20 or 40 years. Or fired clay when allowed to get wet and subjected to  
free/thaw. It can self-destruct within one season.

I would imagine that the limiting factors in determining the longevity of  
a magnesite/sawdust concoction are:

(1) Thoroughness with which the wood fibres are imbued with the MgO  
solution
  (ie degree of preservative penetration/retention by the wood fibre)

(2) Manner in which the structure of the agglomerate handles moisture.
     (ie Does it attempt to exclude moisture entirely (an approach I  
suspect is doomed to failure) or does the structure ahve generous  
interstitial voids that allow for drainage and/or expansion should any  
residual moisture be subject to freezing ?)

But are SBer's here interested in sawdust/magnesite concoctions for  
exterior applications or for floors on interiors ?

If for interiors, I almost have to wonder "Why bother with the magnesite ?"

Some time ago Beel sent me some samples of sawdust + clay mixtures that he  
had made up. I recall doing some unofficial compression resistance tests  
on one of the samples (ie taking it outside and stacking concrete blocks  
on it and doing some quickie arithmetic in my head) and the result wasn't  
too shoddy (although I can't remember what the resulting numbers were at  
the moment. For some reason 75 psi comes to mind but I could be wrong.)

The point is, clay is almost universally available.
Magnesite is not.

If one wants to make a sawdust floor, it seems more than a little bizarro  
to import magnesite from who-knows-where in order to make a supposedly  
more environmentally-friendly floor. The sawdust may be e-friendly but the  
extraction/processing/transportation of the magnesite most likely will not  
be and in the wrong hands could very well result in some el-crappo floor  
that may not even prove to be serviceable.

Me ? If I were interested in making a sawdust floor I'd likely be  
pestering Beel for recipes and fabrication notes on his sawdust/clay  
mixtures that he's been playing with over the years.

If some sort of "preservative" is required so that the sawdust doesn't  
rot, maybe one uses a borate or lime solution to pre-treat the sawdust  
before mixing it with the clay ?


=== * ===
Rob Tom
Kanata, Ontario, Canada
<A r c h i L o g i c   at  c h a f f y a h o o   dot   c a >
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