There are several cleaners available for stripping and/or cleaning the surface of the bamboo flooring. I would suggest trying some in a corner somewhere out of sight, on a small portion before doing the whole floor. Another alternative would be to lightly sand the whole floor down to 'new' wood, then coat the floor with a sealant and/or wax. For specifics, you need to go to the 'Flooring' forum as mentioned by Kudzu, they will point you in the right direction and who to contact for assistance.

It looks like the an area rug was used. In a dining room that would make sense. I would think this is a residue from an area rug....probably one with a rubber/black backing. Maybe even a black felt backing.

Anyway, the first product I recommend for my cork floors (their finish is MUCH more delicate than bamboo) is "rubbing alcohol". For $2 per litre/quart you can purchase some high-strength rubbing alcohol (70% - 90%) at a local drugstore. Go ahead and purchase some plain white cotton cleaning cloths (microfibre if you can) at the same time.

Go ahead and use a SMALL amount on a cloth and rub the stain. Make sure you are in a well ventilated area (open the windows) and always ALWAYS put the cap back on the bottle of rubbing alcohol. It is potent stuff.

I've had plenty of success getting paint spatter and other contaminants off of our cork floors with this method. It is cheap and easy and the alcohol does not damage the finish. This *should be true for any urethane/polyurethane finish.

Good luck. That's a lot of black stuff.

Thank you. Will try in a couple of spots and see if it will works

Success!!! Thank you Canork. With alcohol these abused floors are effortlessly transforming into something decent. God bless you.

Yeah! Good for you! And the finish looks to be in perfect shape! Awesome news! So glad I could help.