Soil - sub base

[mo-uk]

I am in process of re-laying a patio (see separate thread on problem with trader).

Before that a patio had been in place for around 10 years.
And before that it was concreted for 20 years.

So the patio is a rectangle section that goes away from my house and then there is a path which is 90cm wide and 8m long.

The rectangle bit has type 1 on it already and I have leveled it off

With the path what I wanted to do was lower the level. This has meant I have already dug down past the MOT Type 1 sub base that was there

I am down to rock solid mud (not top soil) and I still need to go down another 60mm for my slab and base thickness.

I am going to use SBR in my mortar and I did a test and it foes ROCK SOLID.

So my issue is - do I just vibrate the mud down when doing the type 1 on the rectangle bit and then just lay with the mortar containing SBR

I am 99% sure it will be solid enough but worried of any movement because the path is surround by grass and plants on either side (i.e more soil).

It will be too much aggro to dig down another 10cm and put MOT Type 1 down.

What about a thing layer of concrete at say 25mm? By putting down one solid unit - would thing potentially remove a lot of the risk of slabs moving with ground?

[Tony McC]

25mm of concrete *will* shatter. There's insufficient thickness to support its mass unles syou use all sorts of strengtheners, fibres, etc, so forget that idea straight away!

On thye lower path, what depth of sub-base would you be able to achieve? It may be that, given you have a firm sub-grade, a simple regfulating layer of, say, a 10mm ballast-like aggregate, would be adequate....but are you sure that sub-grade stays firm even when wet?

[mo-uk]

I am somewhat sure but not 100%. I suppose I don't want to do all of this work and take a risk

i could dig more out - how about 50mm of concrete?

I have a lot of type 1 left over from when we dug out so I could re-use it but its all mixed up now so not sure if I could get proportions right.

Also it will cause a BIT of aggro with my timetabling of hiring the whacker plate and I have to wheel it out and in again - so I am inclined just to put something solid down with cement. I could always chuck in some of the type 1 into the mix (maybe not orthodox in terms of it being proper concrete but I am sure it will go rock hard).

Is there any benefit in making the path wider and haunching with material to make it harder for water to get down under the path?

[Tony McC]

The minimum thickness we use for concrete laid without some form of improvement (reinforcement, chemical strengtheners, etc. ) is 100mm.

The Type 1 would be a far better option.

Haunching to prevent water penetrating a pavement? Naaah! That'll never work!

[mo-uk]

OK I have dug down 10cm - so I may as well go another 6 - giving me 10cm base and 6cm for bed and slab

[Tony McC]

All good fun!