Posted: Tue Aug 29, 2017 4:12 pm
Hello all
We have recently had a large extension built and at the end of the build we asked our builder to lay a patio for us. The patio is approximately 8.8 m x 6.4 m in size and laid with Marshalls Wildwood concrete paving slabs (600 mm x 450 mm) onto a full bed of mortar. The work was undertaken during the first few weeks of the year and so the weather was cold on certain days with morning frosts, although the site is not really exposed being between two other houses. The sub base was a mixture of type 1 and crushed concrete bits and of course other building rubble left over from the bigger build so bricks, roof tiles etc which they then compacted down with a whacker plate. The patio was laid in a half brick bond pattern and the pointing contains a dye to match the colour of the slabs. Everything appeared ok until the summer arrived and with it hot dry weather which has resulted in around 80-90% of the slabs starting to rock at the corners slightly when walked on, enough to both hear and see. Strangely when it rains the rocking and movement reduces considerably, although is still present in some of the worst affected slabs i.e. where it meets the bi-folds doors into the house. I wondered whether this had something to do with the rain causing the pointing to expand slightly and reduce the movement? There are small hairline cracks along the pointing at the junction with the slabs and the movement has caused the pointing to break up in some areas. Also when tapped with a rubber mallet some of them sound hollow maybe indicating a gap between the underside of the slab and the mortar bed?. We are in ongoing discussions with our builder who is being difficult about sorting it out arguing that it has been caused by us walking on it although we did not use it for at least 2 weeks after the work was completed and then only in a certain place between A and B whereas the moving slabs affects the entire area although some at the edge ones appear ok. I don't think any of it should move and to fix it properly I suspect will require the whole lot to be relaid unless someone on this forum knows better? the builder appears to think some kind of patch replacement of certain slabs will do the trick but I'm not convinced and I don't want them coming back every 2 months. The installation instructions from Marshalls suggest that the 'backs of the slabs should be primed using a proprietary priming product or fine mortar slurry prior to placement' which I know that they did not use with the slabs simply laid onto a full mortar bed. The builder believes this is recommended for all of Marshalls products and is advisory only and not a mandatory requirement for concrete slab laying - again is that correct?
If anyone has any ideas on what is going on here it would be much appreciated as to be fair to the builder he seems equally baffled saying he has never seen this before and I would not consider them to be cowboys even if patio laying is not the majority of their work.
Many thanks in advance.
Tim
Photos here.....
https://goo.gl/photos/jopFoichkkCLNUds6
We have recently had a large extension built and at the end of the build we asked our builder to lay a patio for us. The patio is approximately 8.8 m x 6.4 m in size and laid with Marshalls Wildwood concrete paving slabs (600 mm x 450 mm) onto a full bed of mortar. The work was undertaken during the first few weeks of the year and so the weather was cold on certain days with morning frosts, although the site is not really exposed being between two other houses. The sub base was a mixture of type 1 and crushed concrete bits and of course other building rubble left over from the bigger build so bricks, roof tiles etc which they then compacted down with a whacker plate. The patio was laid in a half brick bond pattern and the pointing contains a dye to match the colour of the slabs. Everything appeared ok until the summer arrived and with it hot dry weather which has resulted in around 80-90% of the slabs starting to rock at the corners slightly when walked on, enough to both hear and see. Strangely when it rains the rocking and movement reduces considerably, although is still present in some of the worst affected slabs i.e. where it meets the bi-folds doors into the house. I wondered whether this had something to do with the rain causing the pointing to expand slightly and reduce the movement? There are small hairline cracks along the pointing at the junction with the slabs and the movement has caused the pointing to break up in some areas. Also when tapped with a rubber mallet some of them sound hollow maybe indicating a gap between the underside of the slab and the mortar bed?. We are in ongoing discussions with our builder who is being difficult about sorting it out arguing that it has been caused by us walking on it although we did not use it for at least 2 weeks after the work was completed and then only in a certain place between A and B whereas the moving slabs affects the entire area although some at the edge ones appear ok. I don't think any of it should move and to fix it properly I suspect will require the whole lot to be relaid unless someone on this forum knows better? the builder appears to think some kind of patch replacement of certain slabs will do the trick but I'm not convinced and I don't want them coming back every 2 months. The installation instructions from Marshalls suggest that the 'backs of the slabs should be primed using a proprietary priming product or fine mortar slurry prior to placement' which I know that they did not use with the slabs simply laid onto a full mortar bed. The builder believes this is recommended for all of Marshalls products and is advisory only and not a mandatory requirement for concrete slab laying - again is that correct?
If anyone has any ideas on what is going on here it would be much appreciated as to be fair to the builder he seems equally baffled saying he has never seen this before and I would not consider them to be cowboys even if patio laying is not the majority of their work.
Many thanks in advance.
Tim
Photos here.....
https://goo.gl/photos/jopFoichkkCLNUds6