I have finished digging the new pong and started on the edging. The
pond is a little over 4' deep. In one of Helen Nash's books she talks
of firming up the sides by mixing a 1 to 1 ratio of Portland cement
and dirt then applying to the sides before setting in the underlayment
and liner.

Soil here is very clay like, so I think they are structurally quite
sound but it has been raining and I'm worried about the sides eroding
while I do the edging and plumbing work.

Any suggestions on how to get the cement/dirt onto the sides? Any
other ideas?

One other thought I had was mixed up a big batch of mortar then
dipping burlap in it and applying it to the sides.

Any help is appreciated,
Kevin