'Deep' patio needs a lot of hardcore/sub-base...

Eldi_Dos

stuart45 said:

Can be used  with this type of concrete.
Topmix Permeable Testimonial - The ultimate permeable concrete system - YouTube

Watched that, incredible shedding water so fast,thanks for posting it.

boxa

Hi again,

Just to recap a couple of things before I go further forward (& to bed )

Is the consensus to build a new wall inside the current one, using 9”/225 mm blocks (are we thinking something like this https://www.travisperkins.co.uk/product/building-materials/bricks-and-blocks/blocks/215mm-blocks/c/1591045/) .

I’ll then use some screw-on ties, like these?... https://www.twistfix.co.uk/wall-starter-screw-ties to tie in the existing with the new wall.

Finally, how much gap should I have between both walls?

Thanks again and some more questions tomorrow if that's OK 😉

Rosa_Damascena

Hope much is this costing you OP?

stuart45

I'd use these laid flat.100MM 7N MEDIUM DENSITY CONCRETE BREEZE BLOCKS - VARIOUS QUANTITIES | eBay
Ties are fine.
Leave a small gap, inch or so, fill with mortar.

boxa

Rosa_Damascena said:

Hope much is this costing you OP?

We've ballparked, give or take, about 2.5K.

boxa

stuart45 said:

I'd use these laid flat.100MM 7N MEDIUM DENSITY CONCRETE BREEZE BLOCKS - VARIOUS QUANTITIES | eBay
Ties are fine.
Leave a small gap, inch or so, fill with mortar.

Hi Stuart and thanks for the reply.
When you had mentioned 9 inch blocks, I assumed you meant 9" deep/wide.
We have some of the blocks left over from where the fella built the 'retaining' wall, but not enough to build another one. However, from what you are saying I will be able to use those?
He simply referred to them as 'concrete blocks' so if I just get more of those it'll be OK?
It does get a bit more complicated and I'll post a few more pics in a bit - but can I just say I'm really grateful for everyone's input so far, thanks 👍

weeg

Eldi_Dos said:

When our local supermarket was built on a site adjacent to a beach the car parking area was constructed by laying interconnecting crates (looked like upside down bread baskets/ beer crates), they were covered with a membrane and thin layer of hardcore and surfaced. Seven years later and a lot of traffic still looks as good as new. Must be good for drainage and reducing weight.

That'd be these https://www.wavin.com/en-gb/catalog/Rainwater-Stormwater/Attenuate-infiltrate/Geocellular-Units-AquaCell or something very like. Their load capacity is impressive.  Funnily enough I have a client who is looking at putting these under some houses for precisely the reason gabions were suggested earlier - to avoid a wide retaining wall. The manufacturer hasn't agreed to sign off yet.

This stuff https://cordek.com/products/filcor is what we usually use when we can't put in a wide wall.

But usually blocks are the cheap option if there's no reason you can't use them.

stuart45

boxa said:

stuart45 said:

I'd use these laid flat.100MM 7N MEDIUM DENSITY CONCRETE BREEZE BLOCKS - VARIOUS QUANTITIES | eBay
Ties are fine.
Leave a small gap, inch or so, fill with mortar.

Hi Stuart and thanks for the reply.
When you had mentioned 9 inch blocks, I assumed you meant 9" deep/wide.
We have some of the blocks left over from where the fella built the 'retaining' wall, but not enough to build another one. However, from what you are saying I will be able to use those?
He simply referred to them as 'concrete blocks' so if I just get more of those it'll be OK?
It does get a bit more complicated and I'll post a few more pics in a bit - but can I just say I'm really grateful for everyone's input so far, thanks 👍

You can use the old concrete blocks as well. To fill the large cavity between the old stone wall and 4 inch blockwork use a lean concrete mix of around 8/1. Ballast/OPC.
Use about 5/1 building sand/OPC for the mortar.
With regard to retaining walls, their design depends on ground conditions as well as other factors. For example when I lived in Brighton the subsoil is chalk, so you don't get the same problems with hydrostatic pressure you get with a really heavy clay.
I've rebuilt a few 4 inch brick walls into 9 inch that were holding up nearly 5ft of ground for over 30 years. In a clay area they would have been over in less than a year.
The main issues I think you have are the stone face may start to move out in time as it's not tied to the backing wall. 
The fill is so deep at one end that you could get settlement problems in time. You need to make sure the hardcore is well broken down(in the old days it had to go through a 4 inch hoop).  Every foot or so wack it down. Maybe even put a lean mix layer over it halfway to stabilize the fill.

boxa

Thanks again Stuart, I obviously have a lot of head scratching to do but know that with a meticulous plan I can do it, so thanks to all those that have offered advice/support so far.
More concerns now though...
The house (and therefore I assume the steps that used to go down into the garden) have been there since the 1930's.
The fella that built the wall has built both walls (the stone and concrete block wall) onto the existing steps which went down into the garden. I am now a bit worried about the foundations (as he didn't put any new ones in, apart from where the soil is) upon which the walls have been built.
It's a bit of a saga I know, but as long as you don't mind offering advice, I'll keep on posting, so thanks again in advance.

Alter_ego

The side wall in your photo doesn't look up to the job