Cob Is Linseed Oil All You Really Need?

[brad davis]

Hello Fellow Cobbers, Straw Heads, and Other Natural Building Naturals,

INTRODUCTION

The purpose of this experiment is to find a product that will moisture-proof
Cob well enough to build outdoor sculpture like benches, and not worry about
the sculptures washing away or requiring maintanence. Furthermore, this
experiment is a starting point for continual experimentation to determine
what to use, how it can be used, at what quantity, and cost.

Materials- Plaster

Plasters that are generally being used in the Natural Building Movement are
tested. Specifically, hydrated S-type Lime, Gypsum (Plaster of Paris), and
Aliz are tested.  

Furthermore, this experiment follows up on reports of;

1. Pectin being a good binder, and moisture-proofer.

2. Linseed oil being a good mositure-proofer. 

3. Beeswax being a good mositure-proofer.

The following experiment demonstrates some interesting results and finds the
above to be generally true.

A discussion on other products, known to be water resilliant, is given at
the end of this report. One of the more interesting products is "StoneHemp"
(Roman Concrete) that was used to build aquaducts that are still in use 2000
years later. 

Linseed oil

The linseed oil is of the single boiled type.

Pectin

I used pectin crystals that you buy from the store. I dissolved 57g of
pectin in 3/4 cup of boiling water. 

Juices of the Prickly Pear Cactus is generally being used. I got a somewhat
different result by using the crystals. My speculations on why I got a
different result are given in the discussion of this report.


Hydrated Lime

The Lime was previously mixed into a putty about 2 months prior to this
experiment. It is supposed to improve with age. One thing I found is that it
always stayed clumpy no matter how much I mixed it. 

Aliz

This is my second batch of Aliz and again it turned mouldy within hours. I
tried to stop the mould by mixing in borax but this didn't work. I now know
that the flour paste is what is going mouldy. Thus, mix in the paste
seperately to the amount that is going to be immediately used. 

The Aliz consisted of: Flour paste, vermiculite, pectin, linseedoil, clay
slip, and sand.

Materials - Cob

Cob is used, in this experiment, as the medium for the plaster.
The Cob mix was composed of a marine clay, well graded sand, and barley
straw. The clay is not the greatest. It is a sandy, silty clay.
 
PROCEDURE: 

Preparation of Cob

The first step was to make the Cob. The Cob was mixed with sand in a 2 sand/
1 clay by volume ratio, and then enough straw added until the Cob formed a
nice burrito. 

The samples were all made in the 50-100 gram range in the form of balls
since a 100 gram max. scale was used. The Cob samples, of course, were used
as the base for plasters and admixtures to be applied. 

Once made the samples were taken inside and allowed to air dry. It took
about 48 hours for the samples to become completely dry. Once dry they were
again weighed and the moisture content of the Cob was determined. 

Preparation of Plasters

The plasters were mixed in different ratios. Some plasters were mixed with
sand, pectin, linseed oil, and beeswax.

Some samples were made by coating them in one, or a combination of, pectin,
linseed oil, and beeswax rather than mixing these materials in. Only one
coat of a particular substance was applied. 

Two sets of identical samples were made. One set was submerged in water and
the other set was exposed to the elements. 

The Cob samples were plastered with what is to follow. The samples were
weighed wet then again taken indoors for drying until completely dry. The
dry weights of Cob + plaster were measured then one set was submerged in
water and the other placed outside in the elements.

The following are the sets of samples.

Sample(2,10): linseed oil-coated 

  "   (3,11): linseed oil/beeswax-coated

  "   (4,12): 2 sand/1 lime

  "   (5,13): 1 sand/1 lime

  "   (6,14): 2 sand/1 gypsum

  "   (7,15): 1 sand/1 gypsum

  "   (8,18): Aliz-coated
 
  "   (9,20): Aliz/pectin-coated

  "   (16,17): pectin-coated
 
  "   (21,22): Aliz/pectin/linseed oil-coated

  "   (23,24): 2 sand/1 lime/1pectin

  "   (25): Aliz/pectin/linseed oil/beeswax-coated

  "   (26,27): l lime/1pectin 

  "   (28,29): 1 lime/1 pectin/1/2 linseed oil

  "   (30,31): 2 sand/1 lime/1 pectin/1/2 linseed oil

  "   (32,33): 1 gypsum/1 pectin/ 1/2 linseed oil

  "   (34,35): 2 sand/1 gypsum/1 pectin/ 1/2 linseed oil

Set 1 - Submerged 10, 11, 12, 13, 14, 15, 17, 18, 20, 22, 24, 25, 27, 29,
31, 33, 35.

Set 2 - Exposed to Weather. 2, 3, 4, 5, 6, 7, 8, 9, 16, 21, 23, 26, 28, 30,
32, 34. 

OBSERVATIONS 

Submerged-Set 1

The samples were observed in water to see if there were bubbles, cracks and
how hard the surface is. Specifically, the samples were submerged seperately
in glass jars and cans. The hardness of the surface was tested by proding
and scraping the surface with a pen. 

On the final day of observations the samples were also weighed and then
subjected to compression. Specifically, the samples were simply squeezed by
hand and the resistance of each could be felt. All samples, that were not
already broken apart, were broken apart by hand compression. 
 
Day 1 Results - Mar. 20, 1998

10-hard, no bubbles, no cracks.
11-hard, no bubbles, no cracks.
12-hard, no bubbles, no cracks.  
13-hard, no bubbles, some hairline cracks.
14-many bubbles, exploded apart (reaction?)
15-same as 14.
17-generally hard but about 1/4 of sample exploded away. No bubbles, no cracks.
18-broke apart but not as quickly and dramatically as the gypsum mixture.
20-soft, bubbles, no cracks.
22-same as 18.
24-hard, no bubbles, no cracks.
25-same as 18.
27-hard, no bubbles, numerous small cracks.
29-hard (harder than gypsum), no bubbles, few hairline cracks.
31-hard, few bubbles, no cracks.
33-hard, softer than lime, few cracks.
35-same as 33. 

Day 2 Results - Mar. 23, 1998

Change from day one in numbers 18 & 20. Specifically, these samples are now
completely broken apart. All other samples look the same, have the same
hardness, and there are no bubbles.

Day 3 Results - Mar. 28, 1998

Change from last visual observation in 17, 33, & 35. These are now broken
apart. All other samples same hardness, and no bubbles. 

Day 4 Final Observations Including Weights- April 2, 1998

Change in 14, 22, & 25. Thus, 14, 17, 18, 20, 22, 25, 33, & 35 all break
apart on their own in water over a period of 13 days. The remaining samples
are removed from their containers and weighed to determine moisture content.
The samples are then subjected to hand compression and all break apart as
mentioned above. 

Hand Compression

The samples were rated from breaking apart easily to being very resistive to
compression.

The following samples are weighed and then compressed; 10, 11, 12, 13, 24,
27, 29, 31.

10-moderate resistance
11-moderate resistance
12-very resistant.
13-very resistant.
24-breaks easy.
27-breaks easy.
29-breaks easy.
31-breaks easy.

Observations of Samples Exposed to Weather-Set 2

March 31, 1998

2- hard, no cracks, no breaking with hand, by dropping 5ft., breaks with 2
blows of hammer.
3- same as 2.
4- hard, no cracks, broke by dropping 5ft. onto concrete.
5- hard, no cracks, breaks by hand, very resistant.
6- soft, cracks, breaks easy by hand.
7- soft, cracks, breaks easy by hand.
8- soft, cracks, breaks easy by hand.
9- soft, cracks, breaks easy by hand.
16-soft, cracks, breaks easy by hand.
21-soft, cracks, breaks easy by hand.
23-hard, no cracks, breaks by hand, very resistant.
26-hard, hairline cracks, breaks by hand, moderately resistant.
28-hard, no cracks, breaks by hand, moderately resistant. 
30-hard, no cracks, breaks by hand, very resistant.
32-soft, cracks, breaks easy by hand. Unusual in that Gypsum almost
completely washed away. Cob still intact.
34-very soft, cracks, breaks easy by hand. Gypsum completely washed away.
Cob still intact.

Calculations and Results

% moisture = wet weight - dry weight / dry weight X 100.    weight in grams(g).

Sample calculation

2-Set 2.   Linseed oil-coated.    % moisture = 68g - 68g / 68g X 100 = 0%
moisture.

The following are % moistures for samples exposed to rainfall for 11 days
Set 2. The results are presented from best to worst:

2-  0.0 - Linseedoil - coated            X- indicates inaccurate result
3-  0.0 - Linseed oil + beeswax - coated             
8-  2.9 - Aliz X
22- 3.1 - Aliz + pectin + linseed oil - coated X
9-  3.8 - Aliz + pectin - coated X
4-  4.3 - 2 sand/1 Lime 
30- 4.5 - 2 sand/1 Lime/1 pectin/1/2 linseed oil
32- 7.7 - 1 gypsum/1 pectin/1/2 linseed oil
23- 9.0 - 2 sand/1 lime/1 pectin X
16- 10.0- pectin - coated
5-  11.0- 1 sand/1 lime
6-  12.1- 2 sand/1 gypsum
28- 12.7- 1 lime/1 pectin/1/2 linseed oil 
7-  13.2- 1 sand/1 gypsum
26- 17.0- 1 lime/1 pectin
34- nil - 2 sand/1 gypsum/1 pectin/1 linseed oil X

The following are % moistures for samples submerged in water for 13 days-
Set 1. Presented from best to worst:

12-  6.4 - 2 sand/1 lime
31-  7.8 - 2 sand/1 lime/1 pectin/ 1/2 linseed oil
10-  8.7 - linseed oil - coated
11-  9.5 - linseed oil + beeswax - coated
29-  10.0- 1 lime/ 1 pectin/1/2 linseed oil
24-  12.9- 2 sand/1 lime/1 pectin
13-  14.1- 1 sand/1 lime
27-  15.6- 1 lime/1 pectin
35-  44.2- 2 sand/1 gypsum/1 pectin/1/2 linseed oil X

MARGIN OF ERROR

Not all the results are accurate. For example in Set 2 the results show Aliz
works well. However, these results are such because not all the material was
included in weighing. This is because during hand compression the material
flew apart and material was lost. Obviously more care will be taken in
future tests. Hopefully, I will be able to work with precision equipment in
the future other than just a scale.

It rained on the Set 2 samples about every other day during the period.
Amounts of rainfall will be measured in future tests. When it didn't rain it
was cloudy most of the time.

Not all samples were weighed in Set 2 since they fell apart in water.
Specifically, the Aliz, Gypsum, and Pectin samples didn't hold against moisture.

DISCUSSION

Linseed oil & 2 sand/1 lime

Results seem to indicate that Cob coated in linseed oil gives good results
and so does the lime plaster provided it has a high sand content.
Specifically, the samples coated in linseed oil absorb no moisture in
natural conditions and some mositure in submerged conditions. Compared to
the 2 sand/1 lime linseed oil doesn't work quite as well in submerged
conditions and slightly better in natural conditions.

Obviously linseed oil at $ 17 /4L, when used as a coating, is costly for
large works but could be feasible for smaller works. Furthermore, a higher
percent of linseed oil added to the 2 sand/1 lime mix may produce desired
results and be less costly than coating. To complicate matters it is
reported that linseed oils are not alike. Linseed oil and Lime will get
priority in future tests.

Pectin

The pectin doesn't seem to be working as a moisture-proofer, as reported by
others, but definetly as a binder similar to casein and or cement. In fact
lime mix without pectin drew in less moisture. Perhaps the pectin looses
it's moisture-proofing property when dehydrated into a crystal in the same
way that lime becomes an inferior product once dehydrated. Moreover, it is
reported that gel from cacti, are all not of the same quality.

Catholic University of Peru stabilized earthen plaster (Aliz) with Prickly
Pear gel and subjected samples to 20 cycles of simulated rain, each 3 hours
long. The plaster showed only light damage.

The pectin renders S-type lime more workable since it provides a more
consistant mix.

Furthermore, it is very likely that the pectin in the Cactus is of higher
concentration than what I am using. I bought a 57 gram box of crystals from
the store and mixed it with a 3/4 cup of water. 

The reason for using the pectin crystals is the crystals are much more
readily available in my part of the world than Prickly Pear Cactus. However,
Richters in Ontario has Opuntia humifusa available that supposidly grows
well in cold climate. If the gel has the desired quality remains to be seen.
In the southern states the gels are made from Opuntia ficus.

Future Tests

Future tests will concentrate on:

1. Prolonging the duration of a sample of Cob coated in linseed oil under
natural conditions.

2. Coating a sample with multiple layers of linseed oil.

3. Coating a sample with linseed oil then plastering over with the sand/lime
mix.

4. Mixing in linseed oil in the sand/lime mix to a degree, if any, that will
stop mosisture from creeping in. 

5. Hemp oil

6. StoneHemp 

7. Adobe Protector

8. Enviro-loc Does anyone have the website of the company?

9. Palmer Industries "9400"

One problem already known with products 5-9 are they are difficult to obtain
and are expensive. However, the price of Hemp oil, and StoneHemp will
probably drop in Canada now that Hemp is legal. If the price does drop it
will do so slowly since the Canadian Government is choking Hemp as an
industry with many regulations.