[Strawbale] combination rammed earth / strawbales

Patrick FRD patrick at frdata....uk
Wed Apr 19 11:46:10 CEST 2006

As a nwebi I don't know if this is the most appropriate way to reply but

I have also wondered about increasing the U value of rammed earth walls.  

The shuttering for cavity or double rammed earth walls could be very
complicated and time consuming. 

A viable option would be to build a single wall having 3 vertical layers
rammed together.  This could be

1050mm wider shuttering with a 450mm bale wall built in the middle and 300mm
of earth rammed on each side.  This is a very thick wall.  The bale will
move and be compresses during ramming so you will need a well coordinated
team of rammers.  With experiment the rammed earth could possibly be reduced
to 250mm?  You may need horizontal ties to stop it all falling apart
possibly layers of chicken wire.

As an alternative you could use expanded clay beads as the middle insulation
layer.  The beads could be mixed with clay or lime to keep some structural
integrity. If you used 4-500mm shuttering and carefully separated the layers
with temporary separation boards while filling and initial ramming then
remove the temporary boards for final ramming.  This will give a homogeneous
insulated wall.

Alternatively just remove all stones over 5mm in the earth and replace with
expanded clay beads which will probably give the almost the same insulation
benefit as a separate layer of beads and will be much quicker.

Alternatively use a spray machine to apply the render and edge bead.
Assuming you intend your building to be permanent the embedded energy and
the CO2 emissions, involved in using a hired spray machine, will be trivial
over the life of the building will be trivial and probably less that the
energy involved in excavating the earth.  Rammed earth walls particularly
double ones, use a lot of sub-soil and unless you are going to do it by
hand, removing topsoil, excavating and mixing the subsoil, replacing the
topsoil, moving material to site involves a lot of energy.

Having said all of that I think that rammed earth looks wonderful my best
option is Bales with sprayed render for the outer wall and rammed earth for
floors, internal wall, fireplaces and the bottom half or stairs.

Warning ... none of this is tested just ramblings.

On a point of clarity the word LOAM seams to have a Varity of meanings it is
often used in Europe to describe inert sub-soil which would be suitable for
earth walls, but in the UK it is used to describe top-soil particularly
top-soil with lots or organic matter which would be a disaster if
incorporated in earth walls.


-----Original Message-----
From: strawbale-bounces at amper....muni.cz
[mailto:strawbale-bounces at amper....muni.cz] On Behalf Of Ben Albu
Sent: 18 April 2006 22:56
To: European strawbale building discussions
Subject: [Strawbale] combination rammed earth / strawbales

Dear strawbalers,

These days I have been thinking about some things concerning the  
construction of strawbale walls.
I also had a look at the construction of walls with the rammed earth  

Traditional, breathable strawbale wall : loam / strawbale / loam

disadvantages of this "sandwich" construction :

walls are difficult to finish straight, the same problem for the corners.
setting up of a strawbale wall goes fast and easy, but loaming is a lot of  
a loadbearing wall can shrink over time, and loam will crack.

advantages of a rammed earth wall :

construction is easy and goes fast (?)
cheap (in materials, but it requires more loam)
straight and beautiful result
good loadbearing capacities

disadvantages of this type of wall :

poor isolation (for cold climates)

I was wondering if somebody has some experience in making a combination of  
rammed earth / strawbale / rammed earth

If yes ....

Would the isolation properties be the same for this kind of construction  
compared to a classical strawbale wall ?

What about the fire resistant ? Is it advisable to put the bales in  
between without loamfinish ? In Austria they finished a strawbale wall  
completely with wood, but they dipped it in loam before construction.  
Would this also be a requierement if the straw is set up between 2 layers  
of rammed earth ?

Which advantages/disadvantages do you see for this type of construction ?

What about he foundation ?

I am also wondering if the time required to loam a strawbale wall would be  
+- equal to the construction of a rammed earth wall ?

Are there other techniques to isolate a rammed earth wall ? (Not with  
foam, rockwool, etc ...)

Thanks for your help.

Ben Albu

ben at albu...

    European strawbale building discussion list

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