Hand compact sub base for patio

17 Feb 2006
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United Kingdom
Need to fill a small area of existing patio where there used to be a pond. 1m x 1.6m. But the hole is deep. It varies but in some places there will be 300mm depth of sub-base (plus 50mm mortar, plus 50mm Yorkshire flags). This is a patio at the back of the house, it'll never have vehicles on it.

Mot type 1 sub-base is coming Thursday. I was going to do it 'properly' and hire a whacker plate. But now I'm not so sure. It's not really the hire cost that bothers me. It's such a small area, I think I'll actually do more damage trying to manipulate the whacker plate in there, and risk disturbing the sub-base under the existing flags. If that starts to fall back into the hole I'm going to get settlement later. I thought about a trench compactor, but then we are getting into bigger money, and a lot of weight.

So, put it in in layers and compact it with one of those 'hand tamper' things. PavingExpert.com even suggests the bottom of a sledge-hammer. I'd rather buy a sledge hammer than a tamper, to be honest. I'll be doing it with my son, so we can take turns at the whacking. I think I can be a bit more precise with a hand tool than some mechanical monstrosity.

Thanks for any advice.
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You have zero chance of a good result trying to compact 300mm depth using a hand tamper or sledge even if done in stages. If you want to hire then use a trench rammer which has a small foot and is designed for high compaction in small confined spaces.

I would go about it a different way and fill the hole with material that does not need compacting. i.e lean mixed concrete or clean stone. Because clean stone with no dust or graded fines is incompressible it will not have any settlement when in a deep fill. MOT on the other hand will settle a fraction and in a deep fill this will be enough to require the paving on top to be relaid in a few years.

Ideally you would throw down a few inches of stone in the base and then ram that in as hard as possible, then simply fill the hole up with clean stone. Your paving must then be laid on a wet mortar bed to stop any of the bedding draining through the gaps in the stone as would happen if you tried to lay block paing on a sand bed etc. If you are laying stone flags you should be bedding them on wet mortar anyway.

The other option is a lean concrete, It could be as weak as 6 stone 4 sand 1 cement and you could throw lumps of rubble or anything in there to bulk it out.

The gravel method is by far the easiest and cleanest and as long as the gravel is restrained on all sides (i.e the hole doesnt have an open edge) its effective. Its how my own patio is laid which was a 600mm deep fill and how i have dealt with filled in ponds before.

Sorry this is late if you have material coming thursday, perhaps change it to clean stone such as 20mm.
Thanks for the reply. I actually have a heap of old bricks (that came out of the hole). But I don't think these would count as 'clean stone' though? The MOT type 1 is ordered and I'm not sure if I can cancel it at this point.

What I did think about was simply adding cement, then water, to the type 1 to make concrete. What do you think?
Here's a plan then:

1. Cancel the MOT Type 1.
2. Order a load of bagged ready mixed concrete. Chuck (some of it) in the hole. Add water. Mix. I know it's more expensive than ballast and cement, but this makes mixing a bit easier. My 19 year old lad is around to help.
3. Smash up bricks/old concrete flags/anything else solid, and add them to the concrete as I got along, to bulk it out. I've got loads of these old brick.

Lay flags when concrete is ready.

I must sound like a complete amateur here. Believe it or not I spent 5 years in building, quite a bit of that in civils. But our idea of compaction was 5 ton vibrating rollers!
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Your plan sounds fine apart from the mixing bit. I would sooner order some readymix concrete or even readymixed screed.

Throwing some premixed concrete in a hole and watering a bit isn't going to yield a very well mixed result.

I would still recommend using gravel and throw your bricks in amongst it. As long as its restrained its cheap and effective
Thanks. I wouldn't just leave the readymix as is. I'd expect to mix it up a bit. Probably fairly wet and agitate it, to fill the voids between the smashed up bricks/rubble etc. Maybe not bother with the vibrating poker though! I might use postmix. I know it's a bit weaker, main thing seems to be it's not guarranteed for structural stuff. But it's cheaper. The site isn't very accessible. So for the .5 m3 I'd need I'd pay a lot for wet delivered, and either a pump or a lot of barrowing. Chucking the readymix in the hole dry keeps it nice neat. To be honest I was nervous about any sort of vibration, as at the moment all the sub-base under the existing flags is waiting to fall into this hole, then I've got a bigger problem. Filling the hole gently with concrete avoids that.

OK, update. You sort of confirmed the worry at the back of my mind, that 300mm (in places) MOT type 1 sub base might not compact by hand. Especially as I'm concerned about disturbing the existing.

So a bag of local builders ballast (850kg ish), 4 bags of cement, 1 mixer, 1 barrow, 2 teenagers are all being delivered on Saturday. I'll mix it 8 to 1 ballast to cement and bulk it out with my broken bricks, smashed pavings, solid rubble.

I'll leave 50mm for bedding mortar, which arrived today

Thanks for the advice.
Sounds good. Using postcrete or premixed concrete would bankrupt you. Get those millenials to work

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