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You can try something like oxolic acid to bleach out the stains after sanding everything to bare wood. Treat only the effected boards and give them a lot of time to dry out before doing any finish work. Moisture hides really well in red oak. Maybe even use a dehumidifier too.
After that something simple as an oil based clear coat or a shellac and water borne finish might be all you need. a darker stain might fair better to blend it all in.
If the animal oders are too strong you’re probably looking at replacing the effected boards. Take some from a closet for the best match and put new boards in the closet where they won’t be seen. An oscillating tool is great for cutting boards out of an existing floor.

I agree with using oxalic acid. Those stains look like something (urine ?) reacted with tannin in the oak and oxalic acid will usually neutralize that. You might start with sanding the areas so that the acid can penetrate better. If that works, then all you are left with is color matching and finish. Easy

(07-23-2022, 06:16 PM)DogwoodTales Wrote: [ -> ]You can try something like oxolic acid to bleach out the stains after sanding everything to bare wood. Treat only the effected boards and give them a lot of time to dry out before doing any finish work. Moisture hides really well in red oak. Maybe even use a dehumidifier too.
After that something simple as an oil based clear coat or a shellac and water borne finish might be all you need. a darker stain might fair better to blend it all in.
If the animal oders are too strong you’re probably looking at replacing the effected boards. Take some from a closet for the best match and put new boards in the closet where they won’t be seen. An oscillating tool is great for cutting boards out of an existing floor.

(07-24-2022, 11:11 AM)Willyou Wrote: [ -> ]I agree with using oxalic acid. Those stains look like something (urine ?) reacted with tannin in the oak and oxalic acid will usually neutralize that. You might start with sanding the areas so that the acid can penetrate better. If that works, then all you are left with is color matching and finish. Easy

While that’s a time honored way of dealing with the issue, it’s hard to control/ predict the results.