Patio problems

8 Nov 2009
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United Kingdom


We had a new patio laid in June measuring about 3m x 3m. We bought good quality York Stone 35mm thick.

The builder levelled the ground and laid the slabs on a 3-4 inch sand and cement mix.

Within a few weeks the pointing started shrinking and cracking. We also noticed a few loose slabs. By the start of this month we noticed some of the slabs had risen. There are two bad patches, one equalling about a quarter of the patio and the other about 1.5 m x 1 m.

The builder took up the larger area yesterday, this was easy, the pointing chipped out and when the slabs were taken out we noticed the sand/cement underneath had cracked.

The builder randomly dug down a good 12 inches to check for roots - there were none. A fresh lot of sand/cement has been laid and the slabs replaced.

When the builder started on the smaller area today more effort was needed to remove the grouting etc.

The builder is convinced the problems relate to ground movement caused by trees in the area but there is no evidence to support this. The area at the back of the patio and the beds are fine and none of the fences have moved so I can't see how this problem is caused by ground movement.

Can anyone advise what has caused this problem.

Many thanks for your help.

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What was the weather like when the patio was laid? The sand/cement mix used would have been a dry mix. If the patio was subsequently under scorching sunlight, the mix may have dried out completely before it had a chance to set. You should get on better with it being relaid now, cool damp weather. Could be worth stopping it drying out too quickly by covering with polythene for a few days.

Also, is the cement bed retained by a wall, or is there some other way the base is prevented from spreading outwards?
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Thanks for the reply.

Firstly I got the measurements wrong, I should have typed 6m x 6m. I got my maths wrong!

No, the slabs were clean and laid straight onto the sand/cement.


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