Help! type 1 sub base turned to porridge

[greenfingers]

Okay, I dug a hole at the lowest part and no water seemed to be moving in that direction, even though the type 1 is laid at a fall of about 120mm over 6 metres. The sub soil is mainly clay, but is full of stones around 90mm in size and I don't think it poses a drainage problem, because there was no water in it. Also, I tried pulling back the terram under the hardcore and found that there was no water sitting on the subsoil. This suggests to me that it is the type 1 itself that is holding the water.

Anyway, I scraped off the sludgiest bits and put a load of what was supposed to be clean 40mm stone on top (grey coloured, which looks like it is coated in clay). This at least allowed me to run the wacker over it and it is now flat. You can walk and drive over it, but it is still spongy and there are lots of places where water is still trapped on top.

Don't really understand what a composite membrane is. A contractor laid some permeable block paving for me on a new build recently and we had to use about 300mm depth of clean stone with grit on top. Needless to say, it drains perfectly.

What really needles me is that I was trying to do a decent job on my own driveway and now after forking out a grand for three loads of muck away and a load and a half of hardcore, I don't seem to have achieved anything except reduce the levels a bit!

[lutonlagerlout]

when type 1 or MOT as we used to call it gets saturated its purely a waiting game
nothing you can do until it dries out
LLL

[lemoncurd1702]

If you've got a digger on site you could chuck cheap cement over the surface and turn it over with the machine to mix it. The cement will help dry it out.
I've had success with this when there's been problem areas rather than the whole area. Worth doing if you want to get on with the job.

[seanandruby]

A compisite membrane is two layers, the top one permeable and bottom one impermeable. It allows water through the top layer and bottom layer drains the water to trench, from there you can direct the water away to a soakaway, catch pit etc:. Used a lot on permeable paving. Really before any work is started a permeability test should be carried out. On some sub soils it is worth digging that extra out and cap it with good quality crush. Check the mot when it is delivered to make sure it is good quality. It does sound like your first batch of mot was sub standard and holding the water.

[greenfingers]

Thank you guys for the helpful comments.

I've just been out to have a look and nothing has changed since yesterday, so I'll assume the mot is saturated and will dry out eventually.

Now that it's wacked down, it seems unnecessary to add any cement, so I'll hold off for a bit and see what it's like next week.

The composite membrane method sounds like a solution for ground that doesn't drain freely. This is mostly made up ground with large stones in and has always drained fine in the past.

I now realise it would have probably been better to use type 3 at this time of year, which could have had a dressing of dust added in the spring to bind the surface before paving over it.

I will report back in a few days after the drive has had a bit of traffic over it.

[greenfingers]

An update: after a couple of days of vehicles going over the driveway, the clean stone seems to have bedded down further and 'pumped' more sludge to the surface. Also, when you put weight in one spot and make it sink, the area next to it rises, a bit like jelly.

Someone on this forum a while back, explained that movement in a saturated sub base could result in a reduction of the materials resistance to shear, causing it to become thixotropic. This seems to be what has happened here, and presumably is what usually happens if the type 1 is allowed to get wet before it is compacted. Is this situation then reversed when the material dries out?

Today I picked up some bags of cement and sharp sand and tomorrow will try sprinkling a dusting of cement and then the sand over the soft areas. I imagine tracking over it with a digger will bed it into the base and with luck the next day it will have hardened and become impervious to the rain forecast on Wednesday!

If this doesn't work, then it'll all have to come up and I'll get some clean stone down, to at least make the driveway usable for the time being. What do you guys think?

[Dave_L]

I think you're wasting your time.

I think you're going to have to dig the lot up, seperate any useable type 1 for re-use dig down to firm sub grade, geotextile, fill with some bigger aggregate and then use as much as possible of the uncontaminated type 1

[greenfingers]

Thanks Dave, you're right. The sand/cement did form a crust of sorts, but as soon as it was driven on, the surface started breaking up and the mush returned.

Today I dug it out and have a load of 40/20 clean limestone being delivered in the morning. A base layer of larger stone probably would work better, but I really just need a usable surface for the winter. Hopefully the smaller aggregate will bed down flat enough so the kids don't trip over and hard enough by the spring for me to get on with the surface finishes.

Having gone to all this trouble, I am now wondering if it might make sense to tarmac the area which was going to be finished in gravel. Gravel seems to gradually become a mess as it gets contaminated and ground down and I don't relish the prospect of ongoing maintenance. The last quote I had for tarmacing onto a prepared surface seemed a lot, but is this actually a sensible long tern investment?

[Dave_L]

How big is the area for surfacing? A 60mm basecourse would be fine. Is the access OK?

[greenfingers]

The clean stone is now in and seems great. It hasn't been rained on yet, but you can see it will drain okay. It wacked down nice and flat, although not fully bound together like type 1 would be. Big relief and at least the driveway is clean again. Thank you all for your help.

The truck driver saw the pile of mush that had been dug out and said 'did that come from Earthline?' Apparently, some big contractors had had problems with type 1 supplied by them, because they bulk it up with too many fines to make it cheaper to produce. The guy who had done my muckaway supplied the type 1, so when his driver came to collect it I asked if it had come from Earthline and he said yes. I guess that is why he took it away for free!

Dave, the total area is about 250m2, but I am going to block pave 50m2 of that. Access hasn't been a problem before, but the bend in the drive means that 8 wheelers do need to reverse in from the main road.

[greenfingers]

An update and further question for you guys:

The surface seems to have become fairly well consolidated after being driven over for a few weeks. I have scraped off the high spots and wacked it again, so it is now reasonably flat and solid. It also drains off to one side as intended and I was planning to get on with the block paving in the near future.

However, this morning a contractor who had previously quoted for laying tarmac, knocked on the door and asked if I was still considering tarmac (He must have seen the prepared base when driving past). When I explained that I had settled for gravel as a more affordable option, he said he was doing a big job for the Council next week and this meant would be able to tarmac my driveway at a very attractive rate.

Does this make sense? I know he has a fairly well established local company that do reasonably big jobs like car parks and farm estate roads, as well as domestic driveways, so I am confident this is not a cold calling 'Tinker'.

He has offered to lay a 40mm wear course of 10mm tarmac, directly onto my prepared base for £3,750 + Vat. The total area is about 300m2, so my understanding is that amounts to 12m3 of tarmac - is that one 8 wheeler load? I have already done the edgings myself and will install an Aco drain over a soakaway across where the drive meets the road. So the upshot is that I have provisionally accepted his offer to lay a 40mm wear course at £15/m2.

I would be very grateful if any of you could advise me whether this sounds dodgy, or if there is an obvious reason for me to be wary. I remember the problems I had after agreeing to pay an unknown cold caller to tarmac a small driveway - the tarmac turned up before they had prepared the base properly and I had to let them get on and lay it, because he was screaming at me, saying it was going to go off if he couldn't get on with it! Needless to say, it was a terrible job that sank all over the place in no time!

I know the Paving Expert website advocates the use of a binder course under a wear course, but I have previously had a very well reputed firm do a similar job for me where they sprayed the tack coat directly onto my sub base and then laid bitmac on top - it has stood up fine for the last 9 years.

Any helpful suggestions would be great. He has confirmed that he will be using a Bomag 80 vibrating roller (not a walk behind), which is reassuring. I need to confirm the job ASAP.

[msh paving]

nope its a poor job, don't waste your money, you need a binder course simple as that a drive way need to be 70 mm thick for a job 40/30 or 50/20mm,a bw80 roller is ok but very narrow for a bifg area, a 120 is more sensible, up to you, its your money, if he is a good contractor he would not even suggest no base course, and a coincidence he has a big council job just down road, spraying tack coat onto type1 does no good whatsoever , but its your choice my advice would be dont do it MSH

[greenfingers]

Thank you MSH. After he left and I thought it over, the alarm bells started ringing and it's a relief to be able to turn to Paving Expert for sound advice.

I now intend to phone him in the morning to call off the work. It's disappointing, because the preferred option was always to have a tarmac drive, but the two proper quotes we originally had were unaffordable at nearer to £10k all in. Now that I've done the donkey work myself, it would have been great to get it finished nicely and within budget, but perhaps that is unrealistic.

Can anyone out there recommend someone who might be willing to submit a reasonable quote for laying tarmac in Oxfordshire (about 10 miles north of Oxford)? I don't know if it's viable for under £5k, but I believe the total area is actually 260m2. Timescale from now to 3 months.

[lemoncurd1702]

You'd be better off with just base course than 10mm.
Personally if money is an issue have a base course laid with a view to a wearing course later. The base course will give you good service in the meantime.
I'f you're happy with the guy then go with it but insist on a base course which should not cost anymore than 10mm wearing.
Happy days

[lemoncurd1702]

Posted the same time as you Greenfings. £15/m2 probably couldn't buy the material for that. But some contractors who mostly deal with commercials buy themselves cash by doing domestic jobs cheap.