Should I use timber or concrete sleepers for garden edging?

[amySA]

Soon I'll be looking to start establishing some edging in my blank canvas back yard to section grass/gravel areas.

Looking for advice on timber vs concrete sleepers. Looking for them to sit flush with existing garden beds. Currently ground level is around 160mm *variable* to top of beds.

The areas will be filled with garden materials loams/gravel so requiring for the edging to be stable enough to hold the bearing and fine to be almost completely buried. 

I dont have the ability to transport 3m length items so would need to look at smaller sizes and connecting/stabilising. 

Have attached garden sketch for reference. 

 

The main areas I am looking at is the grass areas and the path until it hits the curves.

[MitchellMc]

The sleepers are H4 treated for in-ground use @amySA. This treatment helps protect them against insect attack and decay. Unless you have a solid layer of clay and the timber will be sitting on it and constantly wet, there is no need for additional measures to protect it. However, adding a layer of gravel under the sleepers would aid drainage and minimise the amount of time the sleepers remain wet after rain. 

Typically, H4 posts placed straight in the ground should last at least ten years at a minimum. I guess you need to decide whether the additional work now to get an additional possibly five years outways the work involved with replacing the sleepers ten+ years from now.

Instead of a gravel base, the other option would be to paint all sides under the soil level with Gripset Betta 1L Waterproofing Membrane Bitumen Rubber⁠⁠⁠⁠⁠⁠⁠, as my colleague @EricL suggested. That will effectively seal moisture out from penetrating the lower section.

Mitchell

[amySA]

Thank you, definitely will waterproof with the grips, looks like a great product! 

But yes the ground the sleepers will be sitting on will be quite heavy clay, however it does have some rock through. It does hold water quite heavily which is where the concern comes from. 

[amySA]

Also one further question sorry.. thickness of the sleepers for what I'm trying to do. Would 50mm thickness be suffice or would 75mm be a better option? 

[MitchellMc]

There's no requirement to use 75mm @amySA, and 50mm would suffice. You'd potentially sell less warping of the timber with the 75mm. Likely, your choice would be governed by how distinctive these divisions need to be between the sections.

Mitchell