Paving Slabs Around Pond

[Dana C]

Hi,

We have finally finished digging our pond and fitted the liner and it is now filled with water. My dad is using paving slabs for the edging and is using mortar to keep them in place and will be using cement to fill in the gaps. I read how concrete can sometimes affect the water and how you use sealant and was wondering if we need to do this?

If we do need sealant has anyone got any recomendations?

Thanks in advance for any help.