We've got a plastic pre-formed pond liner that has sunk in one corner.
The liner has a lip that curls outwards and if I could straighten that
out in an upwards direction the extra height would be sufficient to get
a level right across the pond.

Is it possible to deform it? Would, for example, a heat gun soften it
enough for me to get a permanent change?

--
F

On Friday, 9 September 2016 17:34:56 UTC+1, F wrote:
We've got a plastic pre-formed pond liner that has sunk in one corner.
The liner has a lip that curls outwards and if I could straighten that
out in an upwards direction the extra height would be sufficient to get
a level right across the pond.

Is it possible to deform it? Would, for example, a heat gun soften it
enough for me to get a permanent change?

--
F

Not all plastics melt when heated, eg GRP which is the likely one for a rigid pond.
IME your only chance is to drain the pond an reinstall it making sure it's properly bedded in this time.
You'll probably find the plastic has degraded with sunlight/frost around the edge and needs a complete new pond.

In which case a butyl liner is the cheapest/easiest/ most long lasting.

On 09/09/2016 17:34, F wrote:

We've got a plastic pre-formed pond liner that has sunk in one corner.
The liner has a lip that curls outwards and if I could straighten that
out in an upwards direction the extra height would be sufficient to get
a level right across the pond.

It might be thermoplastic but the only way to find out is to try warming
it up. The snag is that unless you can maintain the right tension it
will almost certainly shrink back if it was thermoformed.

Is it possible to deform it? Would, for example, a heat gun soften it
enough for me to get a permanent change?

A better approach would be to add some car body filler or similar and
cover it with the neoprene rubber sold for making ponds. Or expoxy some
lead sheet on which is very easy to work - my pond had a lead shute on
the waterfall and it never seemed to harm the wildlife.

Avoid copper as that willl see things off in short order.

If the stuff has glass fibre visible than there is a very good chance
it is a two part resin cure based casting and will not soften when
heated - at least not before it catches fire.

Regards,
Martin Brown