On 23/05/2011 08:44, Sadge wrote:
Hi, can anybody suggest a cheaper alternative to the rather expensive
ones on the market please?

I think you might have to define better what you mean.

There are waterproof additives for concrete that can be used to make a
sump for rainwater - used to have one like that in a previous large
greenhouse. For small repairs ordinary concrete will do provided you
don't need it to set under water. And there are some polymer compounds
to stop lime leaching out of the concrete and seal any minor leaks.

Regards,
Martin Brown