I am laying a new garage floor which is 5+m by 3+m I am using a 100mm slab (ready mixed) with a 50mm screed on top. Do I need to think about expansion where the slab meet the walls? Will I need any reenforcement to avoid cracking at a later stage? I will use the walls to align the framework and fill in after. Also I am using a screed because I was told that it is difficult to get a good finish on the slab only.