Bill, 60 year old concrete (especially below water) can be very
crumbly I think that's a word. I would try to seal larger cracks
with expandable foam before coating with concrete. Tim is right,
Quickcrete makes an excellent patch product. You must remove all
traces of algae or the patch will not bond. (bleach .... toxic to fish
or mild muriatic acid ..... will cause PH to plunge) Both work well
but you must use carefully.
Fiberglass or epoxy pool coatings are another option, but
very costly. Hank

"Bill Spohn" wrote in message
...
I have an old cement pond that has started leaking after 60 years. I
do not
want to replace it with a membrane, both because I dislike the
appearance and
because I do not want to disturb either the well established margins
or the
large planted island in the middle of it (it is a large pond maybe
40' long).

I have tried patching, but this either didn't take or new cracks
appeared.

I am thinking along the lines of a layer of reinforcing mesh and a
skim coat of
cement to seal it up again, and while I am at it, I'd like to drop
one section
down a couple of feet to allow a place for the fish to hide and the
lilies to
grow - the pond is fairly shallow.

This chore seesm to fall between the areas of competence of the
liner pondies
and a swimming pool company - no one seems to be geared up for the
repair of
existing ponds, though many will offer to install a new one with
membrane,
which is not what I want.

I am prepared to have one more try at patching, if anyone has any
suggestions
for a flexible patching compound that will bond to old concrete. If
that
doesn't work, I guess I may have to talk to the swimming pool people
:-(

Any brilliant iedeas out there?