Rocking slabs - Rocking slabs

[J333]

Hi,

Great website and used on a number of occasions but this is my first time using the forum.

I work as an Architect so I'm fairly switched on when it comes to building practices and concrete, but my expertise on landscaping and laying paving is limited, hence why I'm on here after any advice / opinions from you experts.

Basically I employed a Builder / friend to create a new patio area in my garden. It covers an area approx 18m x 4m. The slabs were laid on 100mm bed of compacted hardcore using a sand / cement mix and then filled with mortar.

On day 1 as I was leaving the house I saw the mix and thought that it looked a little dry (looked like a dry mix floor screed) but kept quiet as I wasn't the one laying the slabs and didn't want to tell someone how to do something they do every day of the week.

However, 3 days later and after letting the patio dry for a further 3 days, I ventured out. Literally the first slab I stepped on, rocked (and not in a good way). I walked up and down the entire patio and literally 80% of the slabs rocked (the worst offenders cracked the mortar join and pushed it out). I called the builder / friend and explained that they were loose, he came back (I was out) and from what I can tell only re-pointed the ones that had pushed the mortar out (we all know that this isn't solving the problem but is just a quick cure until I stand on it).

Getting slightly annoyed I call him back, this time I make sure I'm there. We discuss it and he tells me that due to the shear size of the patio, that the movement in the slabs is due to expansion / shrinkage of the concrete mix used to bed them. I give him the benefit of the doubt, he agrees to come back to fix the loose ones and I'm left with alarm bells ringing telling me that that is nonsense and that the problem is the mix was too dry and in reality it will all need to come up and to start again.

Before me and my friend have a proper falling out, do any of you have any useful advice as to whether you agree with me or if you think it could be down to expansion / shrinkage?

Thanks in advance!

[Dave_L]

Take it up and start again, not fit for purpose.

[lutonlagerlout]

he is talking shite
at least the slabs will come up easily

how often do i hear similar stories to this?

too often
LLL

[GB_Groundworks]

"Builder" such a wide term, has he laid any patios before?

I'm a builder and tony (Luton lager lout) but we are also pavers and so many ppl come on here after some jack of all trades 'builder' has ducked things up.

I suggest you get your friend to spend a day reading the main website here and stop him from fecking up anyone else's patio.

Surely as a architect you could have spec'd it using the British standard etc that's always on our drawings.

Did he using fine brick laying sand as well?

It wants relaying but how many chances are you going to give the guy?



Edited By GB_Groundworks on 1403902850

[sy76uk]

I agree with both LLL and Giles. It sounds to me that he has laid the slabs on a dry sand/cement screed bed. You can get away with that on certain slabs but not all of them and never when you have a mortar joint.

I'm not a brick layer, never have been. I've built a few walls in my time and have done a good on them but my brick work is no where near as good as a time served bricklayer so how some "builders" think that paving comes into there job description because they know how to do it is beyond me.

[dig dug dan]

My comment would be how long after he laid it did you walk on it.
the number of times I have finished laying slabs, to find next morning the customer has been out and done an irish jig on them.
in that instance, the customer pays to put them right.
I will agree that the slabs you are talking about should not have been laid on a dry mix

[GB_Groundworks]

a large unit flag unless on an exposed edge bedded on a full mortar bed using sharp sand and tapped down wont move unless the mix is like piss

I've (20 stone) stepped across newly laid large unit flags albeit in the middle of said slab and not caused any rockers, its more an indication of poor installation than someone stepping on them. although client should say off them for a few hours

[lutonlagerlout]

laying on my wet mix you can walk on the flags within the hour
the type 1 draws the water out
why ? who knows but we have been doing patios and next door other lads doing a patio and our clients were out the next day with a table and chairs ,next door had to keep off for 3 days

if they are rocking its no good
LLL

[dig dug dan]

We tell them To keep off for three days as a matter of course. Customers always stand on the corners, never the middle, and always within 20 seconds of you leaving the site for the day!

[lutonlagerlout]

or the edge of the tread on the steps
LLL

[sy76uk]

I have to agree with Dan. On my last patio we had 3 rocking slabs. All of them between the back door and the step up to the back gate.

The cement needs time to cure and the joints need to be pointed before any pressure is applied to the corners IMO.

[DempseyLiverpool]

I agree with Tony, wet mix with sbr and slurried on flags will take careful foot traffic within an hour or so. Haven't had any rockers for a long time.

Different with setts tho as I lay them on nearly dry mix, like to keep off them for 24 hrs.

[lemoncurd1702]

Definitely a wet mix with a splash of feb, the mix spreads as the slab is tapped, rarely get a rocker. As LLL says can be walked on within a couple of hours though I would avoid unless necessary.
Bit stiffer for the heavy council type.