Ag drain crushed rock

[DIYorPRO]

Regarding crushed rock beneath the ag pipe and above, do you recommend a smaller crushed rock such as 7 mm or larger such as 20 mm?

Also is this okay to lay in the trench?

https://www.bunnings.com.au/grunt-2m-x-10m-black-70um-multi-use-plastic-film-black_p0412365

[EricL]

Hello @DIYorPRO 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your surface drain.

I recommend using the larger 20mm rocks as they produce larger gaps which allows the water to flow faster going down. Whereas a 7mm rock will be more compact and slows the water down as it falls down because of the smaller gap. If you are building a French drain, I suggest using non-woven geotextile cloth for proper drainage. I don't recommend using builder's plastic as this impedes the flow of water.

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you need further assistance, please let us know.

Eric

[Nailbag]

Hi @DIYorPRO 

Definitely don’t use a crushed rock as the powder will clog up and prevent drainage.  I’ve always used 10-20mm bluestone or washed scoria, which are fairly common stone to use. 

Nailbag