Jeff formulated the question :
Why not just use silicon / mastic for the seal ?
imho cement seals look messy and perform poorly

Regards Jeff

I think the idea is to provide a 'dam' around the interior of the wall,
such that it prevents the water flowing in along the concrete base
slab. The idea is not to seal the wall to the slab, which would not
work for long. In my case the slab is a little below the general ground
level at the back and water would tend to build up. I had no problems
with water ingress once the web of cement was put around.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org