I laid 8 limestone paving slabs around 2 weeks ago and unfortunately most have already come loose and can be lifted up. The pavers don't wobble when walked on so I believe they are level but they have not adhered to the mortar. I laid the pavers on a full bed of mortar using a 6:1 mix of Sharp sand and cement as recommended on a number of websites. I cleaned the pavers thoroughly with water to remove debris and then brushed on a diluted waterproof PVA to the back of the slabs before laying. As seen in one of the pics the paving was to sit on a brick wall all around edges and then the middle had been filled with a subbase. The paving appeared to have set and everything seemed rock solid for about 2 weeks and then I noticed one of the pavers was loose, checked the rest by trying to lift and about 3 others moved. What could have gone wrong? It was a very warm day when they were laid, about 25 degrees and the patio is south facing so was getting a lot of sun when drying out. Could this have affected it? I've also read up that maybe I should have used an SBR to help the pavers stick? What are my options now? Is there any way to rectify without having to remove the whole mortar bed and start over?