Damp proofing for garden walls?

6 Feb 2007
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United Kingdom
We are having a block work wall and raised flower beds constructed.

The blocks are concrete.

They will be rendered when finished. Though he has only quoted for our side of the wall to be rendered.

Our bulider has said they do not need a damp proof membrane.

The beds have been filled with soil already with no damp proofing.

I have been assured that the render will have a damp proof aditive.

We are concerned that the damp will eventualy get into the wall damage it.

We are paying good money for a job that is suposed to last us.

We are worried that it wont.

Are our concerns unfounded?

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even really absorbant plaster can suck up and transmit water yet still stay o the wall for years.
You only really have a dpm if you're trying to stop moisture from travlling to somewhere where it can do harm.

The wall will get wet from rain anyway so making any dpm useless.

Additive will do fine.
only needs render one side, cos thats all you will see. A damp course will serve absolutly no purpose what so ever. you dont need it.
If a DPC is inserted into the blockwork it will create a slip joint and you would probably find that the weight of the backfill behind the retaining wall will eventually push it off the blockwork below the DPC.
As for putting a DPM behing the wall this would be pointless.
The only thing that I would potentially change depending on the situation would be to insert drainage from the backfill through the blockwork.
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A DPC in a garden wall which will remain damp is pointless.

However, your problem is moisture from back of the wall and not from the front, or rising up.
The soil will keep the wall damp and blow the render off the face of the wall when it freezes.

The additive in render is to protect from water penetration from the face, not from behind.

What should happen with raised beds, is that a barrier is placed between the wall and the soil, and provisions for drainage are made behind the wall. Even with plain brickwork, the wall can be seen to be damp, or have damp patches which encourage lichen and mould, and efflorescence, and the wall looks generally crap. A membrane behind the wall keeps the wall dry and looking good. Ok, the wall will get wet when it rains, but it will quickly dry. If soil is behind it it will never dry completely

In your case, you wont see this as the render will hide it, but the constant dampness and freeze/thaw cycle will displace the render quite quickly

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