Alex ,floor patch is a cemntitious product that when mixed to a smooth consistancy you can spread on the floor to fill in gaps and voids and wil dry very hard ,but not hard enough you won't be able tosand the roughspots out and make smooth.If you have problem areas you can keep building on top of this stuff to get to the desired heighth.You can get some at h.d. but make sure it is not a gypsom based patch,they are usually white,most manufacturers will not warranty their stuff over it any more cause it has a tendancy to "blow".[8D]
Mr.Captain Bob,i do not expect that you will have any problems with this floor sagging,unless you plan on housing elephan

ts
Floorman
floorlayers union local 1310