Help with Failing Raised Patio after 6 months

[Larastafarian]

 

Hi, We had our back garden landscaped by a contractor last September & we are having numerous issues with it . I have big concerns of how the installation was carried out, the contractor is playing down the seriousness of the issues & keeps telling me they installed everything the right way..

 

Overview of install & issues.

- Back garden was originally on a slope

- Back garden was re-graded & the soil from lower end installed at the new higher end to form the raised section. There was hardcore stone layed on top of this & then slabs installed using a flat bed mortar

- Raised top level area now has tiles that are sinking in areas or lifting / Grout coming loose/raising up out of tiles.

- Upon these issues occuring, I went & researched online to how an install should be done , some things are not sitting right with me despite the contractor claiming the install is done correctly,

1. From what I can tell the raised part is now deemed a retaining wall, there was no perforated pipe installed & soil back filled to the walls with the layer of hardcore on top. The walls were not sealed with anything either & they formed the planters on top of this detail with a kerb

2. An ACO drain was installed at the threshold of the back door , however the tile install up at this higher level is more or less flat with no fall. The water seems to drain through the permeable grout eventually but never drains in to the ACO (Although draining to this ACO would not be advisable as its towards the house). One of the photos below shows how much pooling of water forms when it heavily rains

3. The steps down to the lower level are formed on a soil slope with hardcore layed on the slope- They then hammered in wooden like trestles & back filed the step tread and riser with cement and stone leaving the wooden trestles in situ behind the tread and riser.

4. There are lots of poor cuts around the install - They were just using a hand grinder no water & never used a straight edge ( They have said that's just how its done )

5. The lower part seems to have an extreme fall to the bottom right hand side of the garden ( rather than slope straight away from back of house its falls to the right & towards the back of the garden) upon heavy rain the water just accumulates in the corner there is no drain. 

 

 

Could somebody give me some expert advice on the likely cause of the issues above & how this raised area should have been formed including the steps & "raised beds" so I can review how much the remedial work will be involved to get this right, I know i've been shafted by a really poor contractor here..

 

- How much hardcore stone should have been installed on top of soil?

- How much mortar should the tiles been layed on?

- Should there have been a fall towards the steps/away from the house with a channel slot type ACO drain installed linked into the main storm water drain?

- Should the steps being formed with blocks with the tread/risers cemented to them rather than what they have done?

- Should the planters have been formed like the have, is that an acceptable detail?

- How should drainage been achieved at the lower back? 

 

Photo's are attached with notes

 

 

 

 

 

 

[Roundtuit]

Sorry, not an expert, but a few thoughts are:

- I'd suggest that anything built on 'made-up' ground (ie where soil was moved from bottom to top) is destined to fail.  Are you sure that's what they did?  Building up with compacted stone and type-1 would have been my first thought.

- there should be provision for drainage for the retaining wall.

- there should be some fall-protection guarding on top of the wall.

-any timber used below ground as a structural element would be unacceptable.

 

 

[Mr Punter]

Some of the slabs look like they need levelling and repointing.  The render on the table supports looks like it was done by me.  Overall it is not great but I have seen worse.

 

- How much hardcore stone should have been installed on top of soil?

All the topsoil should be removed and dug down to the subgrade.  Depth depends on soil type.

- How much mortar should the tiles been layed on?

About 50mm solid bed but this would not be permeable.

- Should there have been a fall towards the steps/away from the house

Yes

with a channel slot type ACO drain installed linked into the main storm water drain?

Not necessarily

- Should the steps being formed with blocks with the tread/risers cemented to them rather than what they have done?

Slabs would be supported on risers built in brick or block.  Often infilled with type 1.

- Should the planters have been formed like the have, is that an acceptable detail?

Not sure what the issue is.

- How should drainage been achieved at the lower back?

If you mean the ACO against the house, it is common to see, especially when the paving is less than 150mm below DPC.  It often doesn't go anywhere or collect significant water, but it acts as a barrier rather than having wet sand or soil against the wall.

[Andehh]

Are the slabs loose, rocking or wobbly? The build up isn't ideal if it's made up ground. IANAL but drainage behind that wall, seeing as it has such a large tiled surface covering and heavy rain will make it to the drain, isn't a disaster.

 

Why a cavity wall for retaining? Why isn't the cavity filled?

 

The challenge you've got, is that to fix anything there is a major job. And unless there are material failures, which those photos don't show, you're on a hiding to nothing.

 

If things turn worse in several months, years etc time pry up tiles and relay in flexible adhesive and crack mat...... Being pragmatic, your not gunna want to restart it all.

[Temp]

Made up ground (and the hardcore) should be compacted, probably in layers or it will settle. We used a vibrating wacker plate.

 

In fact all the ground should be compacted.

Edited April 8 by Temp

[Temp]

  On 07/04/2025 at 18:33, Larastafarian said:

 

- Should there have been a fall towards the steps/away from the house with a channel slot type ACO drain installed linked into the main storm water drain?

Expand  

 

They put a linear drain next to the house so there should be a fall towards that. It would be better next to the steps but wouldn't look as good.

 

  On 07/04/2025 at 18:33, Larastafarian said:

- Should the steps being formed with blocks with the tread/risers cemented to them rather than what they have done?

Expand  

 

You can build then many ways. Its quite OK to do..  Compact ground, hardcore, formwork, concrete, remove formwork add paving. Devil is in the detail.

 

 

 

[Larastafarian]

So…. Contractor arrived to site to review yesterday said there may have been some slippage or an “air pocket” which was the cause or sinking & lifting..

 

They lifted all the slabs and wacked the ground with compactor..

 

They started relaying today.

 

I asked them to dig up some of the hardcore out to show me how much they installed before they started laying but never did.

 

I dug a few spots myself this evening as there are too many red flags.. random depts of the hardcore sub base ranging from 25mm-30-40mm in one spot. About 50 in another.. the best I found was nearly 70mm.

 

The tiles they played today had at best 20mm mortar underneath..

I’m assuming this is not correct or acceptable?

 

see photos below… 

[Roundtuit]

Have a look at 'the paving expert' website for an indication of best practice, but that doesn't look good.  Aside from the poor surface prep, I'd still have serious concerns about the stability of the underlying soil if it's been moved from bottom to top: I had my lawn area levelled and compacted with a 17t digger after some tree stumps came out, and it's still settling 3 years later.