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Replies

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  mark harris July 27, 2014 at 9:36pm

  they may sound hollow, but if there is no movement then is no problem,untill any movement is found which on a full wet bet should not happen
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  Stephen Boaz July 27, 2014 at 10:35pm

  Thanks Mark, I agree but I think I need to satisfy the customer with a reason why it's making the hollow noise at all.
• PRO

  Gary RK July 27, 2014 at 10:43pm

  Could it be some of the slabs have inbuilt fracture lines which is changing their sound (ie the same issue when checking Bells etc)?

  One other option is to "test lay" 6 or so slabs elsewhere in the Garden on a full bed, with client present and then return to check them out and prove point ?

  Perhaps one the Paving Supplier members could also pass comment ?
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  David Benson July 27, 2014 at 10:50pm

  hi Stephen were you there when the flags were laid and 100% shore they were all laid on a full bed if so you might have to lift one of the offending flags while they are there to prove it at least go and check the flags yourself different thickness's can sound a different note even if its the bed thickness
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  matt evans July 28, 2014 at 6:34am

  is it a 5 spot style mix in each corner? if so there may be small 'caverns' where nothings touching the slab?
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  Stephen Boaz July 28, 2014 at 10:47am

  Thanks all,
  
  The guys have definitely laid it on a full bed as I insist on it and there would be a mass of sand left over if they hadn't. We have never used the 5 spot technique in 15 years and if any of my team did they would expect to be disciplined! We are planning to use SBR on our next project so its interesting that has been raised and hopefully that is the answer to the problem.
  
  There is no movement in the slabs so is there any arguement for leaving the slabs as they are with a view to carrying out correctional work if they become loose within the next x years? We pride ourself on customer care but obviously cost of unnecessary snagging is also a consideration.
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  Steve London Stone July 28, 2014 at 4:34pm

  This is something that can happen with natural stone. Obviously it could be a sign that the slabs have not properly adhered to the bedding layer but equally it could be an underlying issue with the stone as Gary RK has pointed out.
  
  The best way to see if the slabs haven't properly adhered to the bedding layer is to look at the pointing. Even the slightest movement of the slabs will result in the pointing seperating from the paving slabs.
  
  Obviously you need to satisfy the client so what about lifting one slab just to show that the paving has been laid on a full bed. You could also then have a good look at the slab to see if there is any obvious reason for the hollow sounding noise. If nothing is apparent then its not unreasonable for you to refuse to lift and relay the other 29 slabs. You could back this up with a written guarantee from yourself and your paving supplier agreeing to a lift and relay if any problems occur in the future
  
  Steve
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  Colin Hunt July 28, 2014 at 6:44pm

  I have also encountered had this situation. I lay the slabs, so I know the bed is fine. I think it is due to the layered nature of the slab, where a part has separated, but can not be seen.
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  Thermo July 28, 2014 at 7:36pm

  ill echo the comments, can still happen on a full wet bed that the stone can ever so slightly not adhere, especially in a corner, either through a slight movement as you adjust it or if the slab pulls the moisture out of the mortar too quick in one area. Can also happen with natural faults in the stone. Is it the larger slabs its happening on?
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  Colin Hunt July 28, 2014 at 7:48pm

  I had to return to a Slate patio that had been down a year because 'the pointing on one of the slabs had come away'. When I had a closer look, it was a 600 x 600 slab and the complete top of the slab had come away in one piece to a depth of just 1/4" - the remainder of the slab was solid and 'rang' as it should. Obviously the slab was sound when it went down, so with, heat, cold, wet etc a fault can occur once laid.