Floors, plasters, etc. (long)

[Shannon C. Dealy]

I've been busy for the last 10 days, so I'm just now getting caught up.
I had a hard-drive failure, Fed-Ex lost the replacement, assorted software
problems and attended a workshop on floors and plasters (just in time for
the last week's discussion).

Anyway here's my two bits on a half dozen or so items (that would make
this worth about $1.50 :-).

> To: coblist at deatech.com
> From: "Eric D. Hart" <erichart at mtn.org>
> Subject: Cob floor (long)
>
>
> Shannon Dealy wrote:
>
>> Cob houses tend to use cob floors, it's done in layers starting with a gravel
>> base to prevent moisture wicking up from the ground.  Then a fairly thick
>> layer of regular cob is applied, followed by a couple of layers of a finer
>> cob mix used for finishing.  Finally the top is sealed with linseed oil and
>> bees wax.  I'm doing this from memory, so I may have missed something, I'll
>> dig up my notes and address this in a little more detail later.
>
[SNIP]
>        So if my scheme to use a clay/straw floor will work, what kind of
> recipe should I use?  Steve of SSS said something about a ratio of clay to
> sand.  How does that translate into a recipe?  I realize that it takes
> experimentation but a recipe might help.  I'm also wondering if you need to
> extract clay from the soil you have or you can just shovel in any clayey
> soil you have on a site (and experiment with the amount of sand, etc. you
> need).  I believe Robert LaPorte has a method for extracting clay from the
> soil you have on site.  Would like to just shovel in soil and figure out a
> recipe rather than separating the clay from the soil.     
[SNIP]

Turns out my memory was right about making floors.  The basic cob floor is
done by stripping the top layer of soil containing the organic matter off,
then the ground must be thoroughly packed using a small log to tamp it
down or a pneumatic tamper.  When this is done the surface should be so
tightly packed that the tampers leave little or no dents in the surface.
It helps if the ground is moist (not wet or muddy) when it is being tamped.
Next a layer of gravel is laid (7/8" to 1-1/2" crushed or round drain
rock), it should be a minimum of three inches thick, more in a wet
climate.  You may want to walk around on this layer a bit to settle
it in, it shouldn't pack very much given the large size of the rock.
Get the rock layer as level as possible.  There should be no sand or dirt
in the rock layer, it may be necessary to screen the rock to eliminate the
small stuff.  Over this layer should be placed some old sheets or other
material to prevent the next layer from filling in between the rocks.
Over the sheets place a layer of cob made using a high sand content mix.
Unfortunately I don't have any good numbers for the mix (I know it
when I feel it, some things are hard to describe in print) my best
estimate is that it is about 7% clay with the rest being sand and the
usual approximately 10% straw (NOTE: do not use beach sand in cob mixes as
it is round and does not lock together properly)  The thickness of the
base cob layer should be about the thickness of a 2x4 (1-3/4" thick) this
allows the use of 2x4's to aid in getting the floor even and level.  The
next two layers are each about 1/2" to 1" thick, using the same cob mix as
above, except that the ingredients (straw, sand & clay) are all run through
screens to give the floor a very fine texture.  The straw should
be finely chopped before screening it (unless you wish to devote the
rest of your life to screening straw).  Each cob layer should be allowed
to dry thoroughly before applying the next one.  Once the final layer has
dried, the floor should be coated with boiled linseed oil (not raw), be
careful not to let it puddle on the floor, it must all soak in.
Heating the oil will help it to penetrate faster.  The linseed oil
treatment should be repeated for a minimum of four coats, first coat
full strength, second one mixed with 25% thinner, third one 50% thinner,
fourth 75% thinner.  There is a citrus based thinner available which 
works well.  Finally the floor should be coated with melted bee's wax for
a final seal.

Contrary to my previous posting, I am told that these floors can with
stand almost anything if done correctly, though for maximum strength
you should probably use seven coats of linseed oil.  I'm still not
sure I believe that it would withstand a piano directly on it, but
I'm a novice at floors.

One final note, it is important that the foundation be well drained,
and that the final finished floor be above the exterior grade.  These
two points will help to keep moisture away from the finished floor.


> Date: Mon, 23 Sep 1996 23:28:22 -0400
> To: coblist at deatech.com
> From: patrick newberry <goshawk at gnat.net>
> Subject: Re: Natural (clay) plaster recipe + sequence question.
> 
> sequence of cob house. with adobe floor
> 1. put in foudation
> 2. put up walls         rough in window and doors.      
> 3. put up roof
> 4. put in adobe floor
> 5 finish inside walls

You might want to finish the interior walls before putting in the floor,
while you are working on the walls you will be packing the floor base 
somewhat, and more importantly, you won't mess up your finished floor
with the plasters and/or paints.

>
> Do you imbed electric wires and outlets in the walls?
> What about plumbing?

You can embed all of these directly in the cob, though I would tend to
only run plumbing directly through a wall, and not run it length-wise
in the wall, if the plumbing springs a leak in a hole punched through
the wall, it's easy to remove and the wall damage is minimal, if it
springs a leak in a section run length wise in the wall, its hard to
remove or fix, and more importantly, the water may be trapped in the
wall and cause serious structural deterioration before you notice it.

>Date: Wed, 25 Sep 1996 23:18:59 -0400
>To: coblist at deatech.com
>From: patrick newberry <goshawk at gnat.net>
>Subject: Stucco and earth plaster.
>
[SNIP]
>
>Well I went to a store to find this type-n lime
>all I find is some in the garden shop to be used on one's garden.
>Is this the right stuff?
>If not where should I look.
>I did find some type-n cement. 
>So any way I got some garden lime 
>and type-n cement, what ever type-n means.
>
[SNIP]

I am not sure what type-n lime is, but for all of our plastering work
we used similar mixes, but it was type-S builders hydrated lime
(sometimes it's just marked Type-S, or Builders Lime, or hydrated lime)
it should be available at just about any building supply store.


Shannon Dealy
dealy at deatech.com