Granite setts--driveway build up & q's

[adventuristico]

Good evening Everyone,

Let me first start by saying thanks to Tony! I’ve been lurking around the website for a long while now, and I have finally made the jump into signing in!

I have read loads and loads of pages on website, brew cabin and videos linked to youtube, but I was hoping to have a bit of help for my own personal driveway, if you would allow me to indulge. Many thanks in advance.

I am looking to install a small driveway (6.4m x 5m) that will have reclaimed granite setts (average sizes of L:160mm x W:100mm x D:150mm) installed as a 1m apron at the front and a single sett channel border around the rest of the drive—which will then be filled in the middle with gravel in plastic grids.

Still with me? Great!

Facts:
-sub grade: firm Cheshire sand/clay
-Use: 1 car drive with light daily use- perhaps the odd skip hire
-only can dig max 325mm (due to tree roots)
-the gravel/plastic grid calls for MOT3 sub base (in line with SUDs drainage)
-I am replacing concrete pavers laid onto sand with no sub base


Projected Layout for 1m x 6.4 apron:
Sub grade: solid Cheshire sand/clay
sub base: 75mm MOT-3 (can I use this instead of MOT1 since I will use for gravel as well?)
Bedding: 100mm C20 concrete mix
Setts: 150mm (reclaimed from Liverpool streets) granite setts
Jointing: 3:1 with SBR
Haunching: C20 concrete mix


My questions are these:
-Tony mentions on the rigid construction page that for driveways 100mm is adequate for bedding + base- does this mean a single application of 100mm cementitious bedding or should a lay a separate cement base (50mm) and let cure before starting with the bedding (50mm) and setts?

-should I use a strengthener such as SBR in the bedding?

-Are my build up depths adequate for a 1 car drive?

-Is MOT 3 suitable as a base or must I use MOT1 for the ground beneath the setts?

-Would MOT1 be suitable for some permeability, or is this considered impermeable?

-Am I missing anything?

Again, a massive thanks to you all!

-Sean

[Tony McC]

1 - just use a single layer of 80-100mm ST4/C20 concrete for bedding the setts edges

2 - no need to add SBR to the mix, but use a primer on the underside of each sett as you lay them

3 - you'll really, *really* struggle to achieve a sub-base of Type 3 material at just 75mm depth. I find it's almost imnpossible to use Type 3 in layers of anything less than about 120mm. Why not lay the apron on Type 1 and rely on the adjacent area of Type 3 beneath the cell pavers to act as the drainage? It's how most supermarket car parks are now done: strips of impermeable blacktop laid on Type 1 and shedding water onto adjacenet areas of peremable CBPs laid over a Type 3 sub-base.

4 - although Type 1 is, sort-of permeable, a sub-base constructed using Type 1 is not regarded as permeanble for SUDS purposes.

Does that answer all of your concerns?

[adventuristico]

Hi Tony,

Thank you very much for your reply- it is most helpful!

Just to clarify/repeat- using a MOT1 under the setts with a 75mm depth will be achievable and sufficient to handle 1 car? If so, I will install exactly that.

One other question if you would be so kind:

As far as the drainage for the gravel portion is concerned my layout is the following:

-driveway perpendicular to a gently sloping main road
-Driveway will be levelled, but is currently gently sloped from the road to the house
-Driveway is sand/clay soil mix
-no drainage currently (driveway was concrete paving slabs, downspout runoff straight into hopper into soil --not my doing!)

I am not beholden to SUDS per say, but I am hoping to ensure adequate permeability keep the drive from puddling up. Would a sub base of 150mm MOT1 with a geotextile on top and bottom, followed by 35mm of 20mm aggregate and the groundtrax trays filled with decorate aggregate be sufficient to handle an 18m2 drive ? I am in a difficult scenario as there is no current drainage either to drains or the ability to install a soakaway (I know your feelings on these in clay!). Is MOT1 ok, or as you say in the previous post- MOT3 is a must?

Thanks again!!!

Sean

[Tony McC]

75mm of Type 1 is the very minimum and it's not all that easy to achieve. That extra 25mm, beefing it up to 200mm, makes such a huge difference.

Regarding the cell paver build-up: why would you have a geotextile on TOP of the sub-base? That will act as a slip membrane, which is not what you want!

100-150mm sub-base/25-30mm grit or grit sand/GroundTrax cell pavers filled with deco agg - that's all you need.

[adventuristico]

Hi Tony,

Again- many thanks for taking the time.

I will beef up the sub base below the setts!

Regarding the cell pavers- I only considered the textile on top of the sub base because some manufacturers recommend keeping the sand and sub base separate. I know you only really recommend a textile

As for the sub base- will MOT1 suit for under the cell pavers? I don’t have drains in the driveway, however I am on a slight slope, left to right. The reason I ask is because I believe the builder I hired installed MOT1 and not mot3 (based on the amount of fines I see present) and I am hoping not to dig it all out again.

Also- for being so generous with your time I will be dropping a donation into the website and a matching one in your name at the Warrington foodbank! Thanks for taking the time!

Cheers,

Sean

[Tony McC]

Type 1 is not as good as Type 3 for permeable paving projects but it's still better than the other alternatives.

And if you factor in the (say) 50mm cell paver and then 30-40mm of grit sand laying course, you have quite a reservoir capacity there that will attenuate to the Type 1 which, in turn, attenuates to the sub-grade, so, while it's not ideal, it's really not that bad *on a small residential project*

And I appreciate the gesture, particularly to the local foodbank, a charity close to my own heart.