Sealing an external wall

[Colin]

I have an external party wall that I have had cement rendered. The chap who did it left the bottom six inches not rendered - the rendering "resting" on a metal strip. Looks very good. He said he left the gap so that moisture would not get up the wall so easily and he suggested that I bitumen the bottom two courses. I would rather use a transparent sealer. Any particular type recommended please?

[Tabby]

The bare patch is an evaporation zone. Not recommedned to prevent that happening by sealing it up.

NT