Laying granite setts - Have i specified this job correctly ?

[Joffa]

Hi All

Great site Tony, fantastic wealth of information.

I am undertaking a fairly large project and would like to give you a rough idea of my plans in the hope that you can spot any potential problems before I commit expensive mistakes…

The total area of the driveway is 340 sq m, on a slope and most sections are just over 3m wide. It is a farm driveway so will just have a couple of cars a day generally but does need to cope with the occasional tractor and lorry (oil tanker, cesspit and deliveries)

I am using reclaimed granite setts (roughly 12’x4� and 6� deep). Although it is replacing an existing drive I am going to remove almost all the existing random layers of gravel, tarmac and hardcore to get the levels I want and the depth for the sub base/ bedding. The sub-grade is clay.

I am going to edge the drive with setts set in concrete at right angles to the body of setts.

I am going to use 100mmm of type 1 aggregate compressed with a vibrating roller, this sub base will have a slight camber. I am going to lay 50 mm of bedding sand (class M/zone 2) over that and compress with a vibrating plate, setts will be laid over a period of time and smacked in place with a rubber mallet and once each section completed the vibrating plate used to ensure they are packed down. I am guestimating a compaction of about 12mm (in other words the bedding sand will be laid to 138mm (for a 150mm deep sett) below finish level expecting about 9mm of initial compaction and then 3mm when the setts are 'wackared'), obviously given the differences in height of reclaimed setts some bedding sand will need to be added/removed when laying individual setts. A fine mortar mix will be used to joint them with a sealant used to keep it in and weeds out (probably the resiblock ultra matt – a sample from those really efficient people is on its way…). I know you prefer pitch but the lady of the project is dead set against it.

I am hiring a digger, dumper, roller but thinking of buying a good vibrating plate as the laying may stretch over many weeks. I’ll sell it on afterwards (maybe you could start a ‘classified’ section on your website for this sort of thing ☺).

Can you think of anything I have missed, or anything glaringly wrong – I definitely want to over specify the job as opposed to under specify it.

[Tony McC]

You were doing really well up to the point where you suggested laying the setts on sand and jointing with moretar - it's that old flexible/rigid conflict yet again.

In general, segmental pavements are either rigid or flexible: rigid with rigid joints or flexible bed and flexible joints. If you mix one with t'other, there's problems.

So: you might say that you'd use jopinting (splitt or similar) to suit the flexible bedding, but then you have the problem that your setts are not of a uniform (calibrated) depth, so you have significant variation in bed depth. This laying method would lead to differential settlement over time, and give you a higgledy-piggledy surface.

What you need is rigid bedding: a lean mix concrete should be adequate for the traffic levels anticipated, and then you can use a slurry cementitious jointing to your heart's content.

Probably not what you wanted to hear, but your flexi-rigid combination would see you getting your arse kicked by your good lady in two or three year's time!

[Joffa]

Okay, I see what you're saying - and I certainly want to avoid that arse kicking.

So plan B will be a layer of type 1 (compacted with a roller as before) to form the camber , fill gaps and get the levels right, then a 150 mm base of poured concrete which will need to set for a week, then the setts will be laid in 50/75 mm concrete.

Two questions on this - do I need a minimum depth for the type 1 sub base (in other words should I make it at least say 75mm), and secondly it seems that you would recommend a slurry jointing as opposed to dry fine sand/cement - what are the advantages ?

Thanks very much for your rapid advice - am I glad I didnt jump the gun and start ordering materials n tools yet

A non flexible method does have several advantages for me - as the job could well take some time it means that the driveway will be useable (by foot) as I progress (or not). It also means that the levels are set as the setts laid - non of this art of how much they will compact.

Cheers

Chris

[Tony McC]

I'd go fo a 150mm sub-base and then lay the setts directly onto fresh concrete, rather than pour a base and then lay on top of that with yet more concrete. You can mix your own and so keep pace with the speed of laying, or order in ready-mix: each cubic metre will cover 10m² and if you use a semi-dry lean mix, you should get around 4 hours working time.

Slurry jointing is highly effective and gives a much better job than dry mix jointing. No commercial project would ever countenance dry sand/cement jointing as the resulting joint is weak and crumbly. A wet slurry flows into the joint, filling it completely and 'gripping' the setts firmly. The only downside is cleaning, getting shut of the slurry from the surface of the setts. Over recent years, belt cleaners have been used with notable success and the general consensus is that they produce a better finish than washing or sawdust. However, they need to be hired-in and so represent an additional cost (around 50 quid per week).

A colleague of mine specialising in sett laying still prefers washing-off, but after 30 years in the game, he has got the knack of removing the slurry from the surface without overly-compromising the joint, and his work is, without exception, impeccably clean on completion.

On a commercial project, I would urge the contractor and the client to consider using a resin-based jointing material, as the additional cost is partially offset by the time saved in jointing and by the clean finish, with the added bonus of having a joint that is proven. Alternatively, a gun-applied mortar might be considered for much the same reasons. But on a private, residential project, I'm not always convinced the cost is justified - it has to be judged on a case-by-case basis.

[Joffa]

Tony, thanks for the advice. I am going to look into the price of the resin-based jointing - given the depth of these setts I think this could be prohibitive though.

I'll probably mix as I go, 10m² in 4 hours is probably a tad ambitious given the available manpower....

Will let you know how it goes

[lutonlagerlout]

i take it you are using road kerbs at the edges joffa?
or some kind of restraint?
LLL

[Joffa]

Hi LLL

I'm not going to be using road kerbs exactly - I am going to edge the drive with setts at right angles to the setts in the body of the drive, in the current plan I will have a trench along the edges of the drive with concrete holding these setts in place (the concrete will come to within 30 mm of the top of these setts on the outside of the drive as there is either a decorative aggregate or lawn beside the drive).

Do you think this will be sufficient ?

Cheers

Joffa

[lutonlagerlout]

i don't know what the bs standard is but if you get a grain lorry or something then the load will be pushing the sets out as well as down. maybe one of the civils guys can tell us more?
regards LLL

[SUE @ EASIPOINT]

Hi

On the subject of jointing these setts you might consider a pourable jointing system. This solves the cleaning problem you may have with a slurry and is cheaper than a resin based system. It will also flow to the bottom of the joint and will reach a very high strength.

Check our website - www.easipoint.co.uk and look at the paving section - Easipoint Settpoint is the product I would suggest.

Good Luck!

Sue