Hi, I am laying an extension to our existing driveway by taking out an area of grass down 200mm and then backfilling with hardcore 150mm compacting and adding a layer of 50mm gravel. My question is this, I believe we need to use a permeable sub base, I've been told MOT type 1 is permeable but I don't think technically it complies with building regs so I don't want to use this. Most builders yards haven't heard of MOT3 the permeable stuff? But it was suggested I use 4/20mm Granite for the compacted sub base as this will allow water through and also take the weight of a car. I have no way of checking and there is limited info online re 4/20? Could this be used? Anyone have any idea if it's a good base? I've got to order the stuff tomorrow so before 10 tons arrives I just wanted to double check! Thanks in advance for any advice. Cheers
MOT Type 1 is the most common sub-base for drives, but it technically isn't permeable, when compacted it goes off like concrete and holds water. Clean crushed concrete would do, but finding really clean concrete only crushed is near on impossible, usually full of other rubbish like bits of wood, paper, ETC. Tarmac road planning would too, if you've got someone local who sell them. Is the area dead flat then with no falls at all?
The area will be pretty flat and with the existing concrete edges around the area it won't have a natural run off. The idea is to use a permeable sub base like the 4/20 crushed granite and then a light covering say max 50mm of gravel. Thanks
Many thanks, I'll order the 4/20 granite then. I was also go and buy a membrane tomorrow to lay underneath. What I thought would be a quick job had turned into a huge one! I've had 20 tons of soil to get rid of! Who said gravel driveways were easy! Cheers
After all this rain, I'm surprised you couldn't have compacted the soil nearly 8 inches! Mr. HandyAndy - Really
Another quick question.... I'm ordering the hardcore, area is approx 9 x 7.5m and I'm going down 150mm although some places only 100mm as solid chalk underneath. Roughly I was going to order 12 tons loose for the sub base. Does this sound right? Thanks again!
I would've thought 15/16 tonnes nearer the mark for 150mm, depends on how much area is only 100mm. When laying the hard-core, do it two layers, well compacting each layer as you go.
Closer to 20-21tons @ 150mm depth. Get it direct from quarry if possible, will be lot cheaper & stick 150mm depth over whole area.
Thanks both for replies. I've been quoted 33 per ton delivered including vat for 5/20mm granite or limestone. Is that a reasonable price? Anyone know of any quarries that deal direct in the Kent / Se london area. Thanks again!
Look for Sand & Gravel suppliers ,also Quarries for Kent on Yell. http://www.gallagher-group.co.uk/our-services/aggregates-ready-mix-concrete-and-landfill
Right I've ordered 15 tons of 5/20 granite loose and its arriving on Thursday am so I best get the base prepared! I guess I'll start with the 15 tons and then if I need a few extra I can get them delivered after. I was worried about having loads left over. Thanks for all the replies advice! Just need to hire the wacker plate and buy a wheel barrow now!
Sorry guys another quick question! I've spread one layer of hardcore and compacted, will now add the next layer and compact again for the top layer. I must have went over each area 10 times or more but it doesn't seem to be compacting really tight, I know that's the whole point with it being permeable, the hardcore looks a bit like railway ballast (it isn't and it has a lot smaller prices in) but so you get the idea. I think the top Layer of gravel may mix in with the hardcore and it will then be a grey/gold mixed in mess. Could I put another layer of geotextile on top of the compacted hardcore and then spread gravel or at only 40mm will it show through and be torn up by the tyres? Have uploaded an image so you get an idea of the area. Thanks in advance
Your right in that it won't appear really compacted, that is as you suspect that there's very few fine stone in it. Putting a second layer of membrane is a good idea but it may show through on area of havey traffic, especially where wheels are being turned, my be better with a bit more gravel, 50/60mm, if it's 20mm gravel it should be fine at those depths.
Been a while since you did this, how did it turn out? I am undergoing a similar project nad have been recommended type3 or 10/63 limestone but did wonder if it would compact?