I have white oak floors that were installed 12 years ago and we finally hired someone to refinish them. The first color turned out a lot lighter than I wanted (Duraseal medium brown) so I paid him to re-do it in a darker color that we mixed (1/2 jacobean and 1/2 chestnut). The color was nice but after the poly coats were applied we could see these long waves across the floor opposite the grain (see photos). The contractor was perplexed and thought these were waves that must have been present in the existing floor. Either way, after a night of thinking on it, he decided he wasn't happy with it and wanted to fix it. He then re-sanded and re-stained the floors with our jacobean/chestnut mix. The waves are more mild now but we have a new problem: streaks in the stain. Up close, it looks like a wire brush was dragged across the wet stain in the direction of the grain. From a far it looks like long, light streaks that compete and distract from the grain. (see photos)

https://www.flickr.com/photos/128849822@N08/

We concluded that something was wrong with his sander and he's taking it to be repaired. Any one have experience or an explanation for the streaking? Thanks!

He may have skipped a grit dojng a 36 80 resand with the drum or potentially some of the stain built up on his belt (which may have been the original dulled down belt). Sometimes the uncured finishes are a little gummy and it builds up in lines on the paper creating streaks where no abrasive is in contact with the floor.

The lines perpendicular to the floor might also be because the floor is a little loose, or his sanding machine might have a wheel or wheels slightly out of round.

i hate to say it but that sand job is weak at best in all the photos. The lines you see are from the rough paper, it looks like he skipped from 24 to 80/100. You cant skip more than two grits as you go up or it wont take out the heavier marks. it will just take off the tops like what you have now. Im glad he is working with you but im not sure if he has the skills/knowledge to get it right.