Best way to fill timber frame ready for artificial grass

20 Apr 2021
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United Kingdom
I've got a 4" deep timber frame on top of paving slabs ready to fill in before the artificial grass arrives. The area is 4m x 5.5m.

I have a couple of questions:
- Should I remove some or all of the paving slabs before filling the frame in? Is there any benefit/harm to keeping the slabs?
- What would be the best way to fill in the timber frame? Someone suggested just 3 tonnes of sharp sand, but I heard that would get lumpy and bumpy with not great drainage.

I've got spare soil and stone chips lying around, just in case they could be used to fill in some of it.

Thanks a lot in advance for any suggestions.
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That's a really good article. It says "Spread a layer of 3/8” crushed stone (also called Class 2 Road Base, Decomposed Granite, or Chat) evenly over the area...provided that 3-4 inches of existing landscaping is removed." This assumes I'm digging out an area for the lawn, instead of filling in one that is deeper than the base they recommend. It also doesn't factor in the material sitting against timber, so my use case is a little different to that. I haven't been able to find an article that deals with my particular scenario so thought I'd try to get advice here.
4” of sand would be too thick. I’d leave the slabs and build it up with mot first.
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4” of sand would be too thick. I’d leave the slabs and build it up with mot first.
After a bit of Googling I think this is bang on. Seems like about 80-100mm of type 1, then a layer of weed membrane, then sharp sand for the rest would work.
I’d put a membrane ontop of the sand too or stuff will grow in it.

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