How do you mix premix cement to lay over an existing badly laid cement floor in storeroom?

Answer 1

You will need existing floor to be clean and dry. Layering concrete like this is called a cold joint. Concrete does not like cold joints. That I why big jobs like the cn tower and Hoover dam are all one pour basically.

If you have to do cold joints, clean base floor, rent a sacrifice tool at a rent shop, rough up the floor as much as possible, clean all dirt and dust again, cover floor with a bonding agent from a box store, pour new concrete. Over 2" is recommended.

Another way to get it to hold is to drill holes into base floor or even put various concrete screws in base floor with just the heads sticking up a little bit so new concrete can grab.