Rocking or loose slabs - Patio slabs rock a month after laid

[patiorocker]

Hi,
I had a porcelain patio laid in the high heat of the summer 2018. I live on new build estate which still has houses being developed. After a week of the patio being laid I noticed about 6 slabs were rocking and contacted my fitter. He repaired repaired those slabs by digging them up, removing the cement and then laid them again. Over the following months I noticed more slabs (about 15 different slabs from before) were rocking or created a hollow sound when tapped. So I contacted our fitter again and he sent one of his fitters round and he mentioned it was most probably clay heave. So I said that it would be best to wait another couple of months to get them back to make sure no more slabs became loose. Over those months another 10 slabs were affected.

I contacted the fitter in December to ask if he could repair the slabs but he is denying that it is his problem but he would come and have a look in the new year. Before I get our fitter back I would like to know whether it is his responsibility to correct the issue.

As I mentioned the patio was installed during the high temperatures in July 2018. Up to 150 mm of soil was removed to expose a clay surface. During the 2 week build the clay became rock hard. The fitter had tracked the ground with the mini digger, wacker plated the type 1 in two 50mm layers, laid the paving on a wet full mortar bed with a SBR slurry bond. He tells me I should be able to drive a car on it and it not move, but it has by only walking on it.

If this is clay heave would the fitter be responsible for correcting the loose and rocking slabs?

I spoke to another patio fitting firm that was fitting one of my connecting neighbours patio and they used a steel reinforced concrete base because of it being a new build estate and would be susceptible to movement. This neighbour had a stone resin patio fitted so I am not sure I can compare the sturdiness against mine.

[London Stone Paving]

We had very similar issue at our North London showroom. A crack opened up across the whole length of our display.

Its a tricky one because ultimately the cause of the issue is excessive weather temperatures. The installer could argue that this was outside of his control/act of god.

From reading your post it looks like he has done a very thorough job, compacting the MOT in 2 layers, SBR, Full bed.

My instinct says that its not his responsibility. However, he sounds like a good contractor and form his point of view he will have a reputation to uphold. My advice would be to try and come to a compromise with the contractor. I'm sure if you approach it in a reasonable way he will also be reasonable too.

Good luck

Steve

[Tony McC]

Withouit seeing the site, it's impossible to say with any certainty what might be happening, but it does sound llike a case of clay shrinkage and ground settlement.

The methodology you describe sounds about right, but 50mm layers of Type 1? Why so shallow? That makes me question the size and weight of the plate compactor. The standard minimum depth for a single layer of Type 1 granular sub-base is 80mm.

I would want the installer to provide me with an explanation for the cause, and to prove that cause, otherwise they have to accept liability. If it is shrinkage, as Steve says, it could be argued that it was outwith their control, but ground settlement on new-build sites, particularly where there are lots of drains, is a known problem and could have, indeed should have, been anticipated.

[Highworth paving]

I would check that’s he’s actually used an SBR Slurry, if he has the Mortar will still be stuck on the back of the rocking slabs. Lift one of the loose slabs, if it comes up with no mortar you will be able to request him to relay.
Just a thought
Craig

[lutonlagerlout]

sounds like everything was right except the weather
the 2 50 mm layers is straight out of marshalls
its a sticky one
LLL

[Tony McC]

Regarding those 50mm layers, the *real* reason behiond that advice is that far too many installers lack the correct equipment to thoroughly compact a single layer 100mm sub-base. They use lightweight, cheap vibrating plates that don't meet the requirement of the relevant British Standard, be it part 3 or part 4.

So, instead of insisting installers invest in the right equipment, which would cost perhaps another 300-500 quid for a piece of kit that should last at least a decade, this ineffective "workaround" is proposed, despite the fact that the maximum particle size of a Type 1 granular material, at 37.5mm, renders it practically impossible to construct a sound sub-base of only 50mm depth - as explained here

There are sound engineering reasons behind the requiirements set out in the British Standards, and those reasons are so well-considered and widely recognised that they are "emulated" by equivalent standrads in so many otrher countries with temperate climates. They are *that* good.

So, when someone with a fraction of the knowledge and experience that put together the original standards comes up with what is little more than a 'bodge', I prefer to disregard it and attempt to educate anyone that will listen a sto *why* it's a bodge, and *why* those of us that stick to Standards do things the way we do.