# Forum Home Renovation Retaining Walls  Do i have to use AG behind my retainer wall

## oohsam

Hey all, 
I have almost finished building my retaining wall and was wonder if it is a must to put ag pipe behind the retaining wall. 
I was going to backfill with scorier rock, and have been told weep holes and scorier rock means i dont need ag pipe. 
anyone care to shed some light on this.  
its a timber treated pine retainer wall. 1m high.

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## Terrian

65mm flexi pipe is cheap  :Smilie:  
as a side note, I would use 20mm stone (agg) rather than scoria, the scoria can leech colour, be a shame to stain your new sleeper wall.

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## oohsam

thanks for the reply. 
Ok I'll get some of that stone instead of scorer. I was told that scorer is better to use as backfill because its a very light rock...

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## coffenup

I did not use ag pipe & drainage and my retaining wall is a 2 stage retaining wall with 2 levels first is 400 mm high with a seat & thesecond one is 400 mm again as the back rest. made out of permapine and both walls have started to lean forward with the weight of the soil behind them. If i had to do it again I would put drainage in there and save me the heart ache of having to do it again.
Regards Michael

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## Metung

Unless you have perfectly water tight joints between your sleepers, then I suspect agi pipe is redundant because water will be able to seep out between the joints anyway. I reckon some 20mm crushed rock would be more than adequate.

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## Terrian

> Unless you have perfectly water tight joints between your sleepers, then I suspect agi pipe is redundant because water will be able to seep out between the joints anyway. I reckon some 20mm crushed rock would be more than adequate.

  no, never, 20mm crushed rock has fines through it and will pack down, 20mm agregate is 'clean'

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## oohsam

20mm agg is defenialty the way to go. In regards to the ag pipe, I cant get the ag all the way down the bottom, it will be about 1/2 way up the first sleeper. I'll backfill first with stone and then put the pipe. Is that ok ? Should I put weep holes so water doesnt get trapped in the section below the ag pipe.  
Cheers.

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## Planned LScape

No such thing as too much drainage! 
Just make sure whatever pipe you put in, that it has fall towards the outlet otherwise it's a waste 
Even though flexible or pvc pipe has slots in it and you think that it will leak through to the bottom, it's amazing just how much water flow it gathers from drainage water. Go as low as possible to the bottom of the wall while still getting the fall and it should be ok. Just have the aggregate up at least to 3/4 the wall height so that the water hits the stone and falls straight down to the pipe, instead of creating weight in waterlogged soil

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