I'm sanding my hardwood floors with a rental machine and concerned how using two different grits of sandpaper - 100 and 80, with the latter getting down to the wood in places where I tried to get deeper scratches out - will effect the appearance after a topcoat of polyurethane.

The floors are 75 yrs old and were 'taken down' for the first time 10 years ago, unfortunately before I did a lot of other work in the house, thus they're scratched and the poly is worn in major walkways. I didn't expect to go down to bare wood (and prefer not to, but would like to try to get the noticeable scratches out, for which I've used my hand sander w/80 grit) - and am now concerned whether 'uneven' sanding will result in a splotchy appearance after topcoats of poly.

Is there a conditioner or sealer I can use to be sure I end up with an 'even' appearance. This has been a lot of work so far; I'd hate to have ruined the job in the end.

Thank you very much for any input and/or advice.