I used 8 x 110 mm for the kitchen, but the render and plaster was fairly shallow. On the old part of the house, the render is quite thick, 1/2 inch in places and crumbly. So after the fixing goes through the sheet and render, there's about 35 mm in "solid concrete", but the end of the fixing is tapered, so probably only 25 inch holding. Probably better to go for 8 x 140s? I was able to pull two of the fixings out after hammering in. Possibly cavities in the shuttered concrete walls, bad concrete or spots where the render was extra thick.