pierre-olivier corcos wrote:Hi,
so I'm interested in cob and started to read on the subject. After reading on blogs I tried to make my own and did a couple of test bricks. Now I also started to read the "cob builders handbook" which is very helpful. I must be retarded because I still don't get it.
So here is how I created my test brick:
1) Make your own clay (as per http://ceramicartsdaily.org/ceramic-supplies/pottery-clay/going-local-how-to-dig-and-process-your-own-clay/)
2) Get sand from old sand box from childhood
3) Get dry straw from a random field
4) Mix all 3 ingredient with different clay-to-sand ratio and make test bricks
5) Let dry in garage for a week
5) As shown in pictures
Then I realized that I did not understand what cob was at all:
1) Cob is not as hard as concrete (at least not the one I did) since I could easily break my test bricks in 2 by hand. I read somewhere it was as hard...
2) Cob is not at all impermeable to water (as shown in the picture where I wet a test brick underwater for 30sec and broke it in 2 to observe water penetration)
3) In the "cob builders handbook" it is said that plastering exterior can be done, but it is not necessary
4) I really fear that a non sealed/impermeable/plastered cob wall will disintegrate very fast in time (like in the picture i named "What I believe cob does after 1yr")
5) Finally, I guest that I just don't get it, because I know thousand of people built homes in this material, but as I see it (and what my little experiment showed me) is that cob is a pile of dried earth, maybe able to support a roof and all, but surely not resilient enough to withstand rain and wind. I mean if I rubbed my finger on the test bricks is was crumbling a little and I could easily chip it out with my nails.
6) For example, if I build a cob bench to watch my bonfire, will it not dissolve in rain and snow after a year? And if I drop a fire log on it it will obviously chip?
This is my first post on a forum ever, so that you guys if you take the time to answer!