One idea is you may sprinkle a generous amount of baking soda on the urine stain.
How to get a black stain out of hardwood floor.
Take 150 grit sandpaper and sand the stain directly again along the grain of the wood.
Bleach might have been used to remove the stains from your white clothing but it can do a great job at removing hardwood floor stains as well.
Dip a small brush such as a toothbrush into a small amount of bleach and rub onto the stain.
Apply the paste on the stained areas and let it dry completely.
Let the vinegar sit.
It is best to avoid getting these types of stains as they are difficult to remove but if you already have black urine stains on your wood floors you can attempt to remove them without refinishing the whole area of the floor.
Sand away the stain with 150 grit sandpaper.
Another option is to combine vinegar with baking soda to make a paste.
Soak a cloth in vinegar and apply the vinegar to the stain.
Mix the vinegar with baking soda to form a paste.
For very severe stains sanding won t even get them out.
Allow the mineral spirits to dry.
Repeat for longer hours if the stain is resistant.
Hydrogen peroxide is also suitable for removing the dark stains and the lingering smell on hardwood floors.
The most troublesome hardwood floor stains are those that affect the wood itself.
Make your own hardwood floor cleaning solution by mixing a cup of white vinegar into a bucket of warm water.
Get a soft or microfiber cloth to wipe the paste.
Soak a steel wool pad with mineral spirits and rub the stained area with the pad.
They are usually the result of standing water and are most likely to occur when the finish has worn thin.
You need to remove the finish to bleach these black stains out of the wood and the best way to do that is to sand the affected area by hand with 120 grit sandpaper.
Black rings or dark water marks can be more problematic as these are generally water stains that have penetrated into the finish of the floor.
Oxalic acid is the best to treat stubborn aged stains discolorations like black water and rust stains from your hardwood floor.
The result should then be sprayed and wiped onto the exposed surface of the floor.
Continue sanding until you remove the whole stain.
In order to create the solution you have to make a mixture of one part bleach and four parts water.
Use a soft cloth to wipe the paste and luckily the stain will disappear.
It should help get rid of a black stain on your floor.
Switch to a finer sandpaper once you reach the bare wood.
Soak a piece of cloth in hydrogen peroxide and place over the stain overnight or at least 8 hours during the day.
Since urine is acidic it literally burns the tannins in the wood.