Thanks for the replies, if my memory serves me correctly the tiler was a bit of a stickler to the
rules, i not only got the living room floor done but got my hallway floor done as well, if 18mm ply had been put down i would not have been able to open my front door as this would have brought my existing floor up 35mm and too high for the door, i remember the tiler taking about a day to glue and screw down my floorboards as they were a bit of a mess and lay the plywood screwed at 6" Centres the top and sides were sealed with Bal Bond,
he used a 10mm Serator when laying the floor, can someone tell me after 17 months of no problems whatsoever why is this happening now, it always seems an easy excuse saying ply to thin as this reason is sited on many sites from 6mm to 9mm but 12mm ply, i mean who can really buid there floor up by an additional 35mm