Hi x008164You can use Thin-set with an acrylic admix instead of water to build up the low spots, but the floor drain area needs regular concrete with some 1/8 gravel, and fine masons sand as aggragate to bring it up that much. Actually you may want to consideer leaving it alone. It was placed at that level for a reason I'll bet. Changeing it may change something you dont want to mess with.
Just be sure that is can be concreted over without affecting anything adversly before you pour.
Best, THS
You can use a good stiff wire brush and plain ole water to prep the concrete. If you like you can use a concrete binder to seal the new to the old. The best thing to get a good solid bond is to rough the concrete with a chisel or sharp punch. The rougher the surface the better the bond.
As for the leveling yes that will work just fine. Be sure it is not below 45 degrees. That incluides the slabs temprature. If you pour below 45* the new surface will spall off in short order.
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