Cob RE: spans of thin shell concrete slabs

[Patrick Newberry]

With all this talk of ferro-cement and thin shelled domes etc, I have 
a real life questions with I am to deal with.

I made the (for better or worse) decision to use a multi-layered 
chicken wire and cement roof. Some sections will  use my carpet 
cement as well. Any way I am laying down my vegas (pine, cut and 
peeled by the maukly crew). What I am trying to decide is what span 
should I look at for these vegas (logs used as roof joists)
I have two type sections to deal with. One is a 22 foot dome with a 
bamboo and pine sapling frame in place. Two is a some what low  
sloped roof that extends from the dome to an outer wall (a earthbag 
and strawbale wall combo)

THe procedure I'm looking at is :
On top of the vegas or the bamboo shell of the dome:
1. Lay a layer of 1 inch chicken wire down.
2. lay a layer of tar paper down.
3. lay some type of insulation (rigid?) (suggestions?)
4. More layers of tar paper
5. then multiple layers of chicken wire and then cement this. 
   (or discarded carpet soaked in cement)

First question I face is what distance can I span with this method?

things to think about. One is that I live in a very mild winter 
climate so heating is not hard to deal with. (as in small number of 
days does it get below freezing, but it can get to the teens (F), 
but only maybe once every couple of years and then only for a day or 
so.. Long hot humid summers. 

The underside of this (remember the 1 layer chicken wire and the tar 
paper) I'll plaster with a white gypsum type plaster (a ceiling!).

Money is a consideration:

I could add some 1 x 4's across the vegas but between the "ceiling" 
wire and tar paper to help with span. 

It would be nice to be able to walk at least gently on this for 
repair, inspection etc. 


I also am thinking that I can minimize the up front cost by adding 
only a thin layer of ridged insulation here and latter adding a 
second shell over this at a latter date.  this gets me dry space at a 
lower cost, but allow me to improve the efficiency at a latter date. 
Air flow would occur between the two shells.

Can the ridged insulation sit on the vegas with the thin shelled 
cement roof on top of it and not crush the insulation. 

and as always, Open to other suggestions.

I realize a photo would help, and my last photos got lost in the bit 
bucket, but I found a fellow in MS whom will scan them for me for a 
buck a piece, I'll have them in them mail Tomorrow and he claims 
three working days after he gets them and I'll have them scanned... 
so cross your fingers. 


Pat (busy, tired but happy)
and the rest of the Maukly crew.
http://www.gnat.net/~goshawk
Mauk Georgia