we used 600mmx200mmx75mm. You need ensure that the special premixed mortar for AAC blocks is used. This way there is no sand required to be purchased and not as much mortar needs to be applied. The same goes for render, special premixed. Once the render had dried and was ready for painting we had a plastic skin applied to the render, then the undercoat and then the top coat. With painting we used Dulux paint, BUT if you use that paint you MUST insist on NO watering down of the paint, as Thais love to add stacks of water so the paint goes on easier, but that then reduces the life span of the paint. As a result of using the AAC bricks, which we purchased from Global Warehouse, we don't need to run air con on the lower level, just fans, and in the top floor bedrooms only need air con on for 1 hour before hitting the sack. Noise reduction is pretty good to and the one big thing we've been happy about is no rising damp, especially as the ground water level is only 1 metre below the surface here, and no need for double bricking on the western side of the house.