Patio replacement on slope with horses tail weed

[GettingBetter]

I’d appreciate a second opinion on my situation. I’m very much an enthusiastic amateur and it’s 20 years since I’ve done any paving.

I’m struggling to load images from my phone and will put them up as soon as I can get to a better device.

I have an old patio of slabs on a sand base with concrete blocks forming walls from 50mm below the desired level at one end and 450mm at the other. It slopes substantially (8%) and has a Horses Tail weed problem. I’m fighting the Horses Tail with weed killer but as fast as I kill it off new shoots appear; I’m carrying on in the hope that it will exhaust itself.

I want to lay new slabs on a more level slope, which means filling that part of the roughly 5m x 5m area below a 150mm starting point. I’d fill this with a standard sub-base in 100-150mm layers, compacting down thoroughly as per the write-ups here. Starting with 150 mm all round, I’d do a final sub-base later and 40 mm cement bound bed, initially with individual bedding then moving to screed bedding if I feel confident enough.

I’ll probably leave the old concrete and slabs in place below 150mm and take them up above that depth.

I have a lot of spare Thermalite blocks but think they’re unsuitable as fillers. I may fill in a separate step section, in which case I may mortar them in with spare concrete blocks (210x440x100) on top underneath the sub-base layer.

Am I on the right track?

[GettingBetter]

Patio image

[GettingBetter]

Patio Dimensions

[GettingBetter]

I wait 3 weeks to post this then something else comes along at once.

A neighbour has just started to remove an old conservatory and has offered me the rubble from the old foundations. This gives me the option of filling the void with rubble then laying on a weak concrete mix.