Cob:

[Darel Henman]

Jill,
  the answer is in the text.  A trough is a big tub, usually made out of
wood in the old days, to hold water for drinkgin.   Here it means,
simply a form with, no top and no bottom, for containing the cob mix on
both sides while a mand walks/stomps on the new cob placed there,
tamping it well, while the other pithes up more material.  This is what
keeps the sides so straight.

Some other URL shared by someone about U.K. methods, called this
"shuttering", meaning a form to hold the cob while it gets tamped into
place.  This they called the fast method.

Here's is the explanation quoted from the URL you reffered to us:

"The more modern and improved method of
  cob-walling employed from about 1820 to 1860 is
  that known as "boxing" In which either two long
  planks, laid parallel so as to form a bottomless
  trough, 2 ft. in width, or else a number of smaller
  wooden moulds, about 3 ft. long by 2 ft. wide by 2 ft.
  deep, were placed on the wall, side by side. Into
  these moulds the cob was pitched, the man standing
  inside the mould treading it down until it was filled,
  when the same process was repeated with the next
  mould, the ends of the moulds being made to slide up
  so as to allow the cob in each to unite with that in
  the next.
"


> "Jill cox.net" wrote:
> 
> Can someone tell me how these people, shown making cob home, made it
> so smooth and flat?
> 
> http://www.endersonbrowns.demon.co.uk/cob/index.html