Comments please,
I am refinishing a 2000/sqft red oak floor that appears very old as it is obviously on its last sand job because it is so thin and the house is very old, these are the origional floors.
The floor appears to have been resanded in the last 10 years and stained with possibly an english chestnut stain. My concern is that the homeowner just bought the home and she does not like the large cracks. I explained that the floor is un-even and cracked because of the foundation settling and the lack of humidity. I have been filling the floor with bona filler but it keeps popping out every time I run a pass on my hummel or if I vacuum. Alot of the cracks still have dirt and black filler in them from the last refinish that appears to be flour cement? I did explain to the homeowners that with the age of the floor and lack of humidity the filler is going to pop out again and it is up to them to mantain proper humidity levels above and below the floor. My concern is that I did not state this in the contract and I dont want them coming after me.
My other concern is that the upstairs of the house was a natural color wax shellac floor. I sanded it with 16 grit, 36, 50, then 100 grit and buffed it with 120 but it appears to have orange shellac bleeding out of the pores. How do I avoid this affecting the new stain (dark walnut) and should I seaa the floor with the universal sealer I have been reading about on this website?
Thanks

As far as fillers ,all you can do now is tell your homeowner the truth . However, instead of Bona ,woodline or similar filler , I would much more recommend timbermate. Timbermate holds much better than any of the other waterbased fillers I have used. The best wood filler is actually bondo.Bondo offers a yellow colored wood filler that is basically yellow tinted bondo. It holds incredibly well but the color is yellow and doesn't match with most flooring .

As far as your shellac problem, the only way to tackle it is to buff, let the pores bleed out , buff again and keep repeating until the pores stop bleeding.Putting down one coat of Zinsser shellac as a sealer coat might solve the problem for you.