General question about garden walls and dpc

[Ivor Bigun]

I want to build some raised beds using rendered thermalites. Because I'd like the render to stay on for more than a year or two I'm thinking I need to put in a dpc and bitumastic the back of the wall together with weatherproofing additives in the render.
Is this all too much or does the panel agree?
Are thermalites suitable or is there something better?
Also, there are purpose-built renders from the likes of Lafarge. Does anyone have any experience of them?
Finally, on such a small wall, what prevents the top few courses just slipping off a polythene dpc membrane? Is it just weight?

Ivor

[Rich H]

You don't need (or want) a DPC but bitumastic on the back of the blocks is a good idea. Use dense (concrete) blocks instead of thermalites. I've never used the purpose-made renders, just knock it up myself. Everyone has their own recipe it seems. Make sure that you put in copper pipes at a low level to help balance the soil moisture content.

[Ivor Bigun]

Thanks for the reply Rich. Could a plasterer worth his salt get a polished finish on a mortar render? I'm looking for nice sharp lines.

Ivor

[Rich H]

If you're a novice it's trickier than it looks. Provided the wall isn't massive it's something a plasterer could do on a weekend - scratch coat Saturday, top coat Sunday.