Cob: Cutting holes in cob

[Shannon C. Dealy]

On Fri, 4 Jul 2003, Taylor Publishing-DirtCheapBuilder wrote:

[snip]
> Elishiva said  the cured cob was so hard it took 3 long weeks with a
> pick ax (tough manual labor) to open a small window portal through the
> thick cob.  They assumed it would be easy too...we all keep trading this
[snip]
> Anyone else have an easier time of it? We need anecdotal evidence so the
> real work tally can be known.

The difficulty is going to vary greatly depending on your mix (particularly
if there is alot of rock in it), how dry it is, and how you approach
making the changes.  Depending on what you are trying to do, different
tools and approaches may be better.  Some things I have done:

  - 3" hole through a wall using a hole saw and electric drill, worked
    fine until it hit the core of the wall which still hadn't dried,
    then the cob would fill up the hole saw and I would have to stop every
    minute or two to clean out the hole saw blade unit.  Time to drill
    a 3" hole through 16 inches of cob was about 30 minutes.

  - removing cob from under a window frame to relieve stress due to
    an unexpected degree of shrinkage and settling.  Used an old
    (junk) broad bladed wood chisel and hammer to cut the cob away.
    It took quite a bit of time, but mostly due to making small cuts
    in order to avoid damaging the window frame.   It works quite well
    for precise triming of areas.

  - Reciprocating saw (sometimes called a "saws-all") with a heavy duty
    blade works pretty good for many applications

  - Small hole in a hurry (such as for running wire through a wall), a
    piece of solid steel rod longer than the wall is thick can be driven
    through the walls with light weight hand sledge in about a minute.

I haven't had need of any larger scale holes, though I will need one about
a foot across in the near future.  I suspect that the fastest approach
might be to get or make a large broad bladed chisel with a really long
shaft and drive it through the wall repeatedly to cut the outline of the
hole, then knock the center out with a large/heavy sledge hammer, and trim
the hole afterwards with a reciprocating saw.  Alternatively, it might be
possible to do it directly with a good reciprocating saw and some really
long blades (though probably you would have cut the hole from both sides
in order to get all the way through the wall).  It might be interesting to
try using a wood splitting wedge (I think I have seen some with long
handles) and a sledge hammer to cut the hole.

FWIW.

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
                      |    Embedded Systems, Real-time, Device Drivers
Phone: (800) 467-5820 | Networking, Scientific & Engineering Applications
   or: (541) 929-4089 |                  www.deatech.com