Aerated block flowerbed issue

[ackieboy]

Hi,

My father in law has built me a new flowerbed (me being far too cack-handed for bricklaying), but it has been built with aerated blocks.

I intended to render the top and outward-facing walls of the bed in any case, however I am concerned that the extreme porousness (if that is a word) of the aerated blocks will lead to the render deteriorating very quickly.

Is there anything I need to be doing to the inward-facing wall to waterproof it before I chuck in the loam mix? If so what? Or are my fears misplaced?

thanks

PS Please restrict your comments to the solution to this problem rather than the potentially daft decisions made to date...

 

[marshman]

Best I can think of is paint the backs with Synthaproof,
available from most good builders merchants it is the modern equivalent of cold tar.

 

[imamartian]

What base is the planter on? i would probably line the sides with thick polythene, or pond liner.. and leave the base to drain....

 

[ackieboy]

The base is old crazy paving, laid on top of earth (and the lack of substrate means that there is natural drainage),

I have used a bitumen-based waterproof roofing paint for the inside now, and PVA'd the outside before rendering. Seems to have worked.

cheers.