stone and sand base for flagstones

DIYalot · 13 Aug 2019

Hi. I'm laying flags in my front garden adjacent to the house. I've layed down stones (sandstone) that have come up from my garden (I live on stony ground) - for the purpose of a hardcore base. I've got a 8x8 Roughneck tamper and I've managed to compact the stones. Now, this compaction is not to a professional standard, I mean the compaction does not match what would be obtained by a large roller machine. On top of the hardcore I'm laying down a 1 inch layer of sharp sand. At the moment the sand is damp, not dry.

Q1: So, given that the compaction is not to a professional standard, would it be advisable to lay down a membrane on top of the hardcore and lay the sand upon that?

Q2: Is it OK to lay the flags on damp sand, or should it be dry?

Thank you. Rich

footprints · 14 Aug 2019

Pretty sure flags are best laid on sharp sand cement mix, just done some and that worked fine.
One tip get a slab lifter or two if you have help, simple but brilliant tool!

https://www.tool-house.co.uk/paving-slab-lifter

Got mine from Amazon.

DIYalot · 16 Aug 2019

Hi. OK thread moved into "in the Garden". Reason I posted is because I noticed that when some rain landed on an area not covered by some covering I'd laid down to protect the sand laid down, the sand got washed into my base I'd created. Because of course my base has many voids, not been very compacted. So, that raised the issue of whether my base is compacted sufficiently, even though flags will rest atop of everything. I'm assuming that when compaction is done with a heavy roller, there are zero voids on the base, or very small ones. I'm also wondering if the sand out to be dry when I spread it out on the base I've made.

geraldthehamster · 17 Aug 2019

http://www.pavingexpert.com/layflag3.htm

DIYalot · 19 Aug 2019

Reading the stuff on the pavingexpertdotcom website, given that my hardcore is not so well consolidated, which poses a risk that sand will fall into voids over time, I think "footprints" is spot on by advising the flags be laid on a sand/cement mix. In the words of the paving expert the bed or laying course ought to be (in my case) "hydraulically bound". What I don't want though is to have a cement mix adhering to the flags. And so I'm likely to place a PVC membrane on top of the bedding layer, so flags will not stick to it.

Charlie George · 19 Aug 2019

You can't lay flags like that, most people want flags to adhere to bedding material,is there a reason for wanting it done this way.

geraldthehamster · 20 Aug 2019

Having the mortar bed adhering to the flags is exactly what you do want. It's what's meant by bedding flags.

DIYalot · 20 Aug 2019

In my case the flags are councill flags, i.e. 900mm x 600mm. They wiill be a restraining border around the flagged area, consisting of the front wall of the house on one side and on the three other sides a border consisting of modified flags (300mm x 900mm) laid in sideways. So, these flags are not going anywhere when laid. Which will I think allow me to prevent the flags adhering to the bedding without negative consequences. Anyhow, I prefer that the cement bedding does not adhere to the flags. I'm thinking about laying down a PVC membrane unless there is a product that I can spray onto the flags. Or maybe I could paint the flags with a paint that adheres to concrete, but when dry won't adhere to the concrete bedding. Such as paint for concrete floors.

geraldthehamster · 20 Aug 2019

Up to you, but that is not the way to lay flags. There's no point in using a mortar bed at all, if it's not going to do its job.

scbk · 20 Aug 2019

I would try and fill in the voids in the stones with sharp sand/quarry fines/scalpings/whatever you have to hand, then compact it again, it might need a sprinkle of water.

"council slabs" are fine on a layer of sharp sand IMO

geraldthehamster · 21 Aug 2019

Either sharp sand, if the sub-base is well-compacted, or mortar. Either way, a PVC sheet is not part of the equation.

Best way if not sure what you're doing is to pick one of the methods on the Paving Expert site, and follow it.

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stone and sand base for flagstones

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