waterproof rendered flower bed

[Burnz0]

Hi All. I'm in the process of getting my patio done and the flower bed where the patio meets the garden has just been rendered.
After doing some googling i'm now concerned that ill have issues with water getting inside the flower bed and then soaking through the breezeblocks and blowing the paster off. The chap that did the patio and build the flower bed doesn't think it'll be an issue as he 's filled the bottom half of the flower bed with rubble and any water that needs to drain off the patio itself will also soak into the same rubble.
I've tried to draw something but the issue we had was that the old patio was already on two levels with the entire thing being retained by builders bricks where it met the garden, with those horrible pink and yellow slabs on top of this and then closer to the house there was a concrete slab for a conservatory. Rather than knocking the slab out he raised the level with old hardcore, built the flower bed at the end and then layed the new slabs so it is all one level.
I can't really work out where the water will go and how much of an issue it will be but would rather do something now if possible.
I've read about putting a membrane inside and have already had a go at painting the inside with bitumen paint but since the inside of the bed isn;t rendered all the way to the bottom im not convinced that one layer of bitumen will prevent water getting to the render, especially in the gaps in the mortar.

 

[tony1851]

Rendering free-standing walls - and particularly retaining walls - is never a good idea.
Dampness will always occur from the ground, and the render traps moisture in the wall, leading to risk of damage through
frost- or sulphate attack in some ground conditions.

 

[Burnz0]

any ways of preventing it/minimising the damage now its already been rendered? its too late to go back and start again with normal brickwork and i was going for the white render look i keep seeing

 

[tony1851]

Why not leave it as it is - you might just be lucky.

 

[theprinceofdarkness]

I have this problem in my house, no render, just plants and moss growing on the wall about 3" up from the patio. The raised beds I did myself, I lined the inside of the wall with pea shingle to below the patio level, then hung roofing felt down the wall and sealed the joints. The top of the roofing felt was hidden under coping stones. It worked very well I now see. The only problem was that after some time (ten years?), where the sun got at the small amount of exposed felt, it got rotted through.
I reckon that this summer I will try to line my present retaining walls with "Corex" and gravel.
Frank