My tiler says I do not need 2 coats of mapei wetroom kit on walls just floor and do I need to wait 24 hours before tiling as it is hot today and he said it is dry enough.he has started to tile bathroom walls before tiling the floor is this a good idea.Does the waterproof cement board need priming before tiling.now there is a 23mm gap at the top of tiles by the ceiling and he will have to cut bottom row of tiles 20mm plus height of tiles on floor when he lays them I'm thinking 50mm at the end is the acceptable is it usual to start tiling wall first and from 2nd row up.我已经问他这个 他说这是方法 做它请帮助