Is MOT Type 2 sufficiently permeable for garden paths?

[sandster]

We are converting the back area of our lawn to a veggie plot with gravel paths and raised beds. The ground in our area is dense London clay and our lawn can be home to several ponds after heavy, persistent rainfall. I think a combination of a relatively high water table and very very very slow draining clay soil. I want to make sure we use the right sub base materials for the project. The man we’ve approached does a lot of driveways in the area and also gardens. He suggests we raise the back area slightly (150-200 mm) using MOT Type 2 recycled, topped with a decorative gravel. The area will be lightly used - two of us on foot and the occasional wheelbarrow. My concern is that Type 2 won’t be permeable enough and so instead of lifting our feet (and veg beds) out of the water, we just end up with the ‘ponds‘ forming on top of the Type 2. We could insist on Type 3 but it’s a lot more expensive and he is very insistent that Type 2 will be fine. There won’t be a slope as there is nowhere to drain water to (one side is the lawn, one side is a flower bed, and then we have neighbours either side). Grateful for views!

 

[scbk]

Each to their own but I would make the paths round veg beds out of bark/woodchip. Much cheaper, stone is overkill. My driveway/access road at home is made out of crushed stone at the same depth (150/200mm) and I've had 32ton lorries on it!

It's almost certain you will spill soil/compost on them, spoiling the gravel.

 

[robinbanks]

Is MOT Type 2 sufficiently permeable for garden paths?​

Not really, no. It's great as an underlay under a permeable layer but in itself will leave form a surface on which water can sit when it's compacted and bound together. The water will eventually soak into it and go away, but very slowly. Also, if you have areas where the underneath isn't very permeable either and the MOT stays very wet it doesn't stay bound together if heavily trafficked

Sounds like you should be installing dedicated drainage?

 

[Mottie]

Just spend your time and money on raising the beds.

 

[sandster]

Is MOT Type 2 sufficiently permeable for garden paths?​

Not really, no. It's great as an underlay under a permeable layer but in itself will leave form a surface on which water can sit when it's compacted and bound together. The water will eventually soak into it and go away, but very slowly. Also, if you have areas where the underneath isn't very permeable either and the MOT stays very wet it doesn't stay bound together if heavily trafficked

Sounds like you should be installing dedicated drainage?

Thanks, robinbanks. Installing drainage will be very costly and that end of the garden is not near a drain to discharge water to, so we’d have to dig up a lot of other ground, including concrete areas to connect even if possible. His idea is to raise the height, and effectively create a platform that sits above the standing water. But I assume the platform needs sufficiently permeability itself otherwise that doesn’t work. I think you are confirming my hunch and we do need a sub base with more voids like Type 3 ?

 

[robinbanks]

If you cover your Type 2 with something permeable that doesn't wear too thin (needs maintaining to keep its depth) then it doesn't matter so much that the water permeates the Type 2 slowly; your surface is relatively free of standing water even if it's underneath. Water that doesn't pond on your platform will run off and pond somewhere else (or keep running) - if that's acceptable because, say, you're looking at having a lawn that can cope with very wet soil and no plans to walk on it in winter months then raising the parts you want to walk on (paths) and between (beds) means you end up dry enough.

If the platform is level or slightly dome shaped it could be completely impervious to little overall effect (other than displacing X tonnes of water that would have sat in the ground where the platform now is). If it ends up a bowl shape then it creates its own elevated standing water pond; just be careful with the shaping of it/ensure it falls to somewhere that won't be trafficked, have one end (or center) slightly higher - all easy to do with MOT - tI'd aim to have the ground falling towards vegetation you want to keep - e.g if flowers one side and lawn the other, a peak towards the lawn side means the platform acts as a water collector for the beds, which might otherwise have a small surface area between larger areas that water doesn't permeate. Arranging such can mean that the flower beds don't have access to as much water as they used to

ps; realise that this sounds like a reversion against what I said earlier but I'd somehow taken away the impression that the Type2 was going to be the visible surface!

 

[sandster]

Thanks again. Yes, we’ll have decorative gravel on top. So it’s clay soil at the base. Platform of type 2 above (edged by sleepers or similar to retain the platform). Then gravel top layer. Water should quickly drain from gravel onto Type 2 but I worried that if type 2 takes forever to drain then we’ll still be walking in water. I suppose that for that to happen, water has to be deeper than the gravel layer. And even if it is, wellies keep us dry. The more important thing is we will be walking on a stable surface. In the current situation the problem is not just that it’s wet, it’s that the ground is so muddy it’s impossible to walk on without destroying the grass and picking up a kilo of mud on the base of your shoe! Thanks for your advice and thoughts. V helpful. You have completely understood the issue.

 

[robinbanks]

If the platform of type 2 has a very slight angle (referred to as a fall, and is unnoticeably shallow like 1 inch of height loss for every 80 inches of horizontal travel) then it won't pond. Water that doesn't percolate flows off sideways instead. It's easy to arrange with granular material; you just put less of it on one side than the other when raking it out and flattening. A spirit level placed on the ground will show its bubble offset rather than central between the lines. If your guy puts it in dead level, you can ask for it to be reshaped but even dead level will be fine so long as it isn't dish shaped with a low point in the centre and as you say, the depth of gravel only has to be greater than the depth of and standing puddle in a localised depression

You can get plastic trays to help retain gravel in position, by the way, which may save you some faff in raking it back into place periodically as it moves around. If your gravel is very fine and quite deep it will actively inhibit moving a wheelbarrow on it; you'll either enjoy the extra workout or not so choose a coarser gravel or thinner depth if you want a "path of least resistance"