Double Skin wall to retain Patio

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Not sure if this is "Building" or "In the Garden" Forum, but here goes.

I need to build a small retaining wall, approx 450mm tall. I have dug out and laid footings 450mm wide by 200mm deep, min 150mm below ground. The wall I intend to make will be from heavy frost resistant blocks, double skinned, two blocks tall. I have the following Q's and observations. (Ground is heavy Devon clay)

1) When you use these blocks for a double skin, should there be a mortar layer between the skins or should they butt up?
2) Should the second skin overlap the first by half a block?
3) I plan to use wall ties for more strength.
4) I think I need weep holes to alleviate hydraulic pressure, do I do this by leaving a gap in the mortar or use an SDS drill when finished and insert some 22mm copper every metre? (if I leave a gap in the mortar, this may conflict with Q2..)
5) I plan to put a damp proof membrane behind the wall to stop water leaching.
6) The Blocks will be faced up with Patio Slab material.

Thanks for any help!
 
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[quote="tnarg999";p="1054278"1)
When you use these blocks for a double skin, should there be a mortar layer between the skins or should they butt up?
there should be a 10mm gap betwixt skins for a mortar joint. avoid overfilling this joint as it will tend to push its neighbour over.

2) Should the second skin overlap the first by half a block?
you could lay one course flat if you wish this would tie the two skins in.

3) I plan to use wall ties for more strength.
you could if you wish or do as above.

4) I think I need weep holes to alleviate hydraulic pressure, do I do this by leaving a gap in the mortar or use an SDS drill when finished and insert some 22mm copper every metre? (if I leave a gap in the mortar, this may conflict with Q2..)
we use square gutter down pipe, as it is less difficult to cut square, it corresponds with metric brick courses and it is adequate size. 22mm copper would clog up in no time.

5) I plan to put a damp proof membrane behind the wall to stop water leaching.
sounds ok to me. or paint it with a bitumastic paint. whatever floats yer boat.

6) The Blocks will be faced up with Patio Slab material.
:?:
 
Thanks Noseall

Quote:
6) The Blocks will be faced up with Patio Slab material.
:?:

The face of the blocks will have on edge flags fixed to them, to match the rest of the patio - it'll only be 300mm visible, so should look ok.[/quote]
 
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