I suppose you mean 1mm butyl liner, here in the states we call that
..040 or 40 mil rubber/roofing liner. It is very resistant to rock
abrasion or tearing when stepped upon, by people, a deer hoof may
punch through, but little else is likely to damage it enough you will
notice in your lifetime.. I have one rubber liner, one plastic formed
and one Permalon liner pond and consider the rubber the toughest,
because it resists abrasion better than Permalon, even though the
Permalon is rated as being stronger.

The white overlay will develop a normal coat of algae and change color
to match the bottom and sides, which will coat with algae too. The
overlay may be a curious sight waving with any current, but soon will
be almost invisible unless you are fortunate enough to have gin clear
water. Personally I wouldn't have put anything over the rubber before
throwing in the rocks. I kept a pond this way for a couple years,
but vacuuming the rocks out to clean the bottom became more of a task
than I can handle, so I cleaned out the river rock and use the pond
for floating plants now.

Regards,

Hal

On Fri, 1 Sep 2006 08:41:43 +0100, "Davy"
wrote:

Just to clarify my post; I have put a patch of underlay on top of the lowest
part of the black butyl and then a bed of gravel on top of the centre of the
underlay (now probably better called overlay!). About 10 inches of white
underlay extends beyond the edge of the gravel and it is this that is
shining through. I cannot trim the underlay since the gravel would then too
easily get under the underlay. Also the exposed edge of the underlay is not
lying flat against the butyl - it billows up a bit. It can only be a matter
of time before some of the gravel finds its way under the 'billows' and may
then damage the butyl. Any thoughts?

cheers Davy

"Davy" wrote in message
...
Just installed a new wildlife pond. The water table is a bit high here so
I
weighted the liner down with some stone; and to protect the butyl liner I
put some underliner (overliner?) down on it first.
Filled it for the first time today and the pure white overliner shows very
distinctly. The pond is 5m by 6m and about 50cm deep.

Is it likely to improve?

Davy