Frost heave - I'm having problems with a builder...

[Brian1]

Hi
I'm looking for help with a dispute I'm having with a builder. I should preface by saying I did email Tony about this in outline but things have moved on since his helpful reply.
Basically I'm wondering if I'm barking up the wrong tree or if my interpretation of things is reasonable. So here goes -
I live in Glasgow and in Sept - October 2010 our builder laid a patio of Marshall's Heritage Calder brown slabs on clay ground using the dab mortar technique. (I'm afraid I don't know about mortar consistencies or what foundation was used). Towards the end of the big freeze I went on holiday for a week, when I returned a number of cracks had appeared in the slabs. The largest crack is about 10 feet long and follows a rough line round the site of our new conservatory but only appears in the slabs themselves, the mortar is cracked in very few places and most of the time the line of the crack stops at the edge of one slab and then seems to continue on the next slab without breaking the mortar. There also didn't seem to be much evidence of the slabs themselves moving but the crack probably did coincide with a period of thaw.

Marshall's and the builder attributed the cracks to 'frost heave' and the builder said due to this he couldn't be held responsible for the damage. Marshall's have said they don't recommend the dab method, stating it can result in water gathering under the slabs and also say when a full mortar bed method is used frost heave shouldn't occur.
From reading this site and emailing Tony I've gathered the dab method doesn't fit with the British Standard nor Marshall's recommendation for laying the slabs. The builder disregards this and says the dab method is fine for the job they did ie a domestic patio.

Finally I had a patio on that ground before (pre conservatory) and last winter there was no evidence that the old slabs there had cracked or moved despite a similar period of prolonged cold.

So my take is three things could have happened -

1. Frost heave unrelated to any building technique, basically its bad luck on my part despite never having frost heave on that ground before.
2. Slabs crack due to an intrinsic fault in the slabs (Marshall's deny this is the case, but I haven't really pushed them on it)
3 The slabs cracked due to frost heave worsened by water accumulating in the gaps in the dabs, freezing and breaking the slabs.

Does anyone have any views, or advice. Have I just been unlucky and is the dab technique OK for a domestic patio?

All help welcomed! I can probably post pictures of the cracks if that would help anyone.

[ilovesettsonmondays]

hi , the dab / spot method is a fail . full beds underneath slabs . job has been laid incorrectly without any frost being taken into consideration

[mike builder/landscaper]

this is no way to lay a patio. 100mm-150mm of type 1 stone should have been layed and compacted. then full morter beds to support the paving. you are right to suggest the voids underneath have filled with water, frozen, expanded and caused the cracking.

[lutonlagerlout]

they will have to come up,no pro would lay on dabs it is a pure fail
it really angers me when the big boys gang together on things like this to try and mug punters off


anything you pay for should be fit for the purpose for at least 12 months
thats the law
LLL

[Brian1]

Thanks for the speedy responses, that's very helpful. I know its a stupid question and I think I pretty much know the answer, but I assume there is no circumstance in which the dab method would be acceptable for a domestic patio?
I just want to be clear as the builder is telling me 'we've done it this way on lots of jobs with no problems and everyone we've spoken to say its OK'.
I'm kind of assuming that's garbage, or at least if its true for them they've been lucky not to have had problems before.

[London Stone Paving]

Not if you want to the patio to last for any period of time. You have been particuarly unlucky with the speed and extent of the damage but even in the very best circumstances dabs dont last, they start rocking after no time at all and once they start rocking they are as good as knackered

[Mikey_C]

have you paid him yet?

[Brian1]

Yes, damn our foolishness, it happened 2 weeks after the final payment for the job.

[London Stone Paving]

I used to work as a labourer for a reputable landscape contractors in Stoke (10 years ago) and all the guys there used to lay in spots. It was only when I moved to a differrent company that I was shown that paving needed to be laid on to a full bed. I think its more widespread than people realise.

[Tony McC]

Brian,

I know we've discussed this via email, but the answer you seek is actually in your post above.

I've said that spot/dab bedding is NEVER acceptable. This is repeated over and over and over again on the website, which, though I say it myself, does tend to promote best practice at all times.

Then, the biggest paving manufacturer in Britain, Marshalls, have said that they do not recommend spot bedding.

BS 7533 Part 4 requires flagstones to be laid on a full bed of mortar, and this specifically covers patios (although patios and other caterory IV pavements may also be laid on a full bed of sand).

Yet the arsey builder/patio layer is claiming that spots are adequate.

Who do you think a court would side with?

[Brian1]

Many thanks for all the replies, its all been very helpful, when I'm being hit with a builder denying everything and not knowing much about building at all you start doubting whether or not you are right.
Its reassuring to know that you all think I am right!
Cheers guys.