Thorfun Posted June 20, 2021 Share Posted June 20, 2021 the structural engineer has designed free-draining stone as our backfill material for around our basement walls. The groundworker is giving me an option between shingle and graded crushed rock chalk. the rock chalk is cheaper. what are peoples opinions of which is best to use and why? I will ask the SE but as it's Sunday that will have to wait so I thought I'd ask the knowledgeable folk on here to get opinions as part of my own research. Link to comment Share on other sites More sharing options...
Ronan 1 Posted June 20, 2021 Share Posted June 20, 2021 What has the rock chalk been graded to ? I'd say shingle would be very expensive option for the volume around a basement rock chalk would do the job IF it's graded suitably Link to comment Share on other sites More sharing options...
Oz07 Posted June 20, 2021 Share Posted June 20, 2021 Will the chalk clog up over time? Link to comment Share on other sites More sharing options...
Thorfun Posted June 20, 2021 Author Share Posted June 20, 2021 3 minutes ago, Ronan 1 said: What has the rock chalk been graded to ? I'd say shingle would be very expensive option for the volume around a basement rock chalk would do the job IF it's graded suitably Not sure on the grading sorry. What would a suitable grading be? Link to comment Share on other sites More sharing options...
Thorfun Posted June 20, 2021 Author Share Posted June 20, 2021 3 minutes ago, Oz07 said: Will the chalk clog up over time? This is a very good question and hopefully someone smarter than me will be along soon to assist. I assume if it did it would be the crushing that allows it to happen as isn’t chalk permanently permeable in its natural form in the ground? Link to comment Share on other sites More sharing options...
Ronan 1 Posted June 20, 2021 Share Posted June 20, 2021 3 minutes ago, Thorfun said: Not sure on the grading sorry. What would a suitable grading be? Something like a 20-40mm clean (503). This finer grading can be harder got with some chalk hence why it's worth asking. 1 Link to comment Share on other sites More sharing options...
Ronan 1 Posted June 20, 2021 Share Posted June 20, 2021 3 minutes ago, Thorfun said: This is a very good question and hopefully someone smarter than me will be along soon to assist. I assume if it did it would be the crushing that allows it to happen as isn’t chalk permanently permeable in its natural form in the ground? Chalk is fairly permeable as an in place stratum. Once crushed if there is too much fines it can hold water and slow it's release hence my comment above 're grading 1 Link to comment Share on other sites More sharing options...
Oz07 Posted June 20, 2021 Share Posted June 20, 2021 Limestone clogs up doesn't it? Link to comment Share on other sites More sharing options...
Thorfun Posted June 20, 2021 Author Share Posted June 20, 2021 15 minutes ago, Oz07 said: Limestone clogs up doesn't it? That’s what I’ve heard before. And chalk is a limestone. But does 1+1=2? but maybe it’s the dust in limestone that causes it to clog? And so a washed and suitably graded chalk might not clog? Link to comment Share on other sites More sharing options...
Ronan 1 Posted June 20, 2021 Share Posted June 20, 2021 16 minutes ago, Oz07 said: Limestone clogs up doesn't it? Any stone will if it's not graded as clean, I like using limestone as a rule it's a good hard rock that binds well and I like it for free drainage too in either a 20 to 40mm clean or a 3"clean. The secret is some terramm and clean the area your backfilling first to hard ground Link to comment Share on other sites More sharing options...
Thorfun Posted June 21, 2021 Author Share Posted June 21, 2021 12 hours ago, Ronan 1 said: IF it's graded suitably Found out they’re suggesting it is graded 50 to 75mm size. Link to comment Share on other sites More sharing options...
Thorfun Posted June 21, 2021 Author Share Posted June 21, 2021 Also found this recycled stuff https://soilsandstone.co.uk/recycled-aggregates/recycled-shingle-gravel/ think this is the sort of thing that @Bitpipe used. Wonder if that might be cheaper still? ? Link to comment Share on other sites More sharing options...
Ronan 1 Posted June 21, 2021 Share Posted June 21, 2021 Yes that recycled gear would do grand, 2 to 3 inch clean and your flying 1 Link to comment Share on other sites More sharing options...
Bitpipe Posted June 21, 2021 Share Posted June 21, 2021 Ours was larger, fist sized rocks that looked to be a a mix of brick, road surface and rock. Worked well though. The two things you're looking for is something that will drain freely and that will not settle over time. The recycled shingle looks good but have they looked to get the clean stone? On one stretch of our backfill (at rear, where the patio now is) the ground worker ran out of stone skimped and used site spoil. This would have been OK if compacted with a whacker every 150mm but that obviously never happened and the area slumped quite significantly during the above ground build and has settled ever since. Happened the one week I was off site. Even when the landscaper whacked the surface and laid another 50cm of hardcore, it's still settling and the patio slabs are no-longer flat. Will need addressing at some point. Link to comment Share on other sites More sharing options...
Thorfun Posted June 21, 2021 Author Share Posted June 21, 2021 2 minutes ago, Bitpipe said: and used site spoil. our SE has said we can't use the clay spoil as the walls aren't designed for the load that clay will give. Link to comment Share on other sites More sharing options...
Thorfun Posted June 21, 2021 Author Share Posted June 21, 2021 3 minutes ago, Bitpipe said: Ours was larger, fist sized rocks that looked to be a a mix of brick, road surface and rock. Worked well though. these guys https://robinsofherstmonceux.co.uk/supplies/aggregates/ do recycled concrete cobbles (2" - 4"). think I'm going to ask the groundworkers to use this stuff. Link to comment Share on other sites More sharing options...
Bitpipe Posted June 21, 2021 Share Posted June 21, 2021 Just now, Thorfun said: our SE has said we can't use the clay spoil as the walls aren't designed for the load that clay will give. Thankfully our site spoil was a gravely mix with chalk , problem is it has taken ages to settle in the area where it was used. Link to comment Share on other sites More sharing options...
Bitpipe Posted June 21, 2021 Share Posted June 21, 2021 Just now, Thorfun said: these guys https://robinsofherstmonceux.co.uk/supplies/aggregates/ do recycled concrete cobbles (2" - 4"). think I'm going to ask the groundworkers to use this stuff. Exactly what we had. 1 Link to comment Share on other sites More sharing options...
Adam2 Posted June 21, 2021 Share Posted June 21, 2021 Also used clean 40mm recycled stone for a large back-fill - it's great as so quick to place. Though you do get the odd tap/other surprise items in the recycled but generally very good with no fines 1 Link to comment Share on other sites More sharing options...
Thorfun Posted July 8, 2021 Author Share Posted July 8, 2021 (edited) hi all. I have another question on the backfill and am also looking for opinions. How high should the free draining stone be filled to? i.e. should I top it off with site spoil? if so, how much? 40cm? 60cm? 100cm? or should the backfill stone be taken up to the top of the basement walls? The SE drawings show stone to the top of the walls in places but also says "Ground level (to architects detail)" which isn't that helpful. we're not exactly sure what we're going to do around the perimeter of the house yet but maybe some small shrubs, or maybe a path, or maybe just laid to lawn so it's hard to know exactly what to cater for. we will have some drainage for the roofs where the backfill will be and that is approx 600mm below FFL (FFL is approx 275mm above the top of the basement walls). At the moment I've told the groundworkers that I'm happy with 60cm - 80cm of site spoil (i.e. clay) above the backfill (on top of geotextile of course) and I can then put topsoil on top of that if gardening or just dig it out down to the backfill if patio/path. too much spoil? not enough? can you tell I'm confused as to what to do? Edited July 8, 2021 by Thorfun Link to comment Share on other sites More sharing options...
Oz07 Posted July 8, 2021 Share Posted July 8, 2021 Think I'd be taking up to ground level but not familiar with the standard practice Link to comment Share on other sites More sharing options...
Thorfun Posted July 8, 2021 Author Share Posted July 8, 2021 12 minutes ago, Oz07 said: Think I'd be taking up to ground level but not familiar with the standard practice thanks Oz. I'm also not familiar with standard practice! hoping @Bitpipe will be along soon to tell us what he did but I'm liking your thinking tbh. maybe not to ground level though, maybe to the top of the basement walls as per the SE drawing? Link to comment Share on other sites More sharing options...
Oz07 Posted July 9, 2021 Share Posted July 9, 2021 You could cap it with some decorative gravel I'd of thought. To me it looks like the drawing asks for it to come up to ground level? 1 Link to comment Share on other sites More sharing options...
Onoff Posted July 9, 2021 Share Posted July 9, 2021 Shouldn't there at least be a layer of geotextile above the bulk of the backfill with a say decorative (if the bulk fill material doesn't suit), topping over that? Otherwise, over time, small debris particles will filter down. Link to comment Share on other sites More sharing options...
Thorfun Posted July 9, 2021 Author Share Posted July 9, 2021 1 hour ago, Onoff said: Shouldn't there at least be a layer of geotextile above the bulk of the backfill with a say decorative (if the bulk fill material doesn't suit), topping over that? Otherwise, over time, small debris particles will filter down. I’m putting geotextile on top of the backfill. Link to comment Share on other sites More sharing options...
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