Normally after a screed, there is a topping material such as tile or timber or laminate applied. The material of course provides the designer the option of color, texture, durability etc. In this case, the problem with a bad screed is not immediately obvious, but would show over time especially with timber and laminate topping.For a pure screed flooring, a problem is almost immediately obvious; for example sandy surface etc. The components of a screed are sand, cement and water, mixed in the correct proportion and the right way. It is fairly simple, until a contractor chooses to use an inappropriate sand, or less cement or more water or anyhow mix them. And almost all the subsequent defects seen in cement screed flooring are caused by this contractor action. Next is the preparation before pouring the screed; there is a minimum thickness of screed to comply, the floor slab to be examined and vacuumed, and wet the slab (some would apply a coating material to help bonding of screed; same purpose of the sealant before painting a wall). And the screed is not supposed to be done on a raining day, when the air humidity is higher. And then the screed is poured and leveled, and left to cure, It could take up to 7 days to properly cure the application depending on the environment condition. So it is fairly simple, the process is similar to baking a cake, until a contractor chooses to shorten the time and start using (or apply epoxy on) the floor before curing is completed etc. Where epoxy is to be applied, the key is to first make sure that curing is completed. Epoxy is of course a coating, adding a skin to the flooring. An epoxy application is a mix of epoxy and a hardener; when mix correctly in proportion and method, and left to cure properly, it would not be sticky or tacky. Later I would write the process you would like to see a contractor take in rectifying the situation in this case. There is also the need to remove all furniture in the area and put in place protection before the start of the process. Good luck!