I just moved into a new house and they had prefinished hardwood floors. They were scratched but I also have a large dog. I was worried that with such little wear surface on these floors, I would benefit from extra layers of urethane. I lightly sanded the floors and put water based urethane on top. I lightly sanded between each layer. Now the urethane is peeling off. I did not sand much. Did I not sand enough? Should I have used an oil based urethane? Can I screen the peeling urethane off? They are Green Mountain wood floors. Please, I need help!

I just had the same problem in not sure of what to do with prefinished oak flooring I installed over 10yrs ago. After researching I decided to remove the prefinish. Sanded down to bare wood. Most manufacturers recommend not trying to recoat prefinished floors. One or two say it was OK if you followed their system, which involved more steps than just sanding. I used Polopalz Supreme (http://www.poloplaz.com/products/reside ... upreme.php) You will have to sand now that it's peeling. One of the more experienced pros, can give you a more definitive answer.

You did not sand enough and the finish is not bonding.The same would happen with an oil base.

The best way to prepare a prefinished floor to accept a coating is to abrade it with a wire brush/abrader.
Even with this, it is then helpful to apply a coat of shellac first as a bond coat..then your topcoating finish of choice.

now that you have a failure, you need to sand the flooring down completely.

James, can I screen off just the material that is peeling off, or do I need to screen all the way down to the wood? Would you use a buffer to screen it or would you use a drum sander? I am afraid a drum sander would eat too deep into the wood. If you use a buffer to screen it, would grit would you use? Thanks for the help.

Unfortunately you will need a full resanding to bare wood.
No otherway once bond has been lost.

Pooler,
In the past I've used a drum sander, but seen too many professionally finished floors with drum marks. A non professional probably wouldn't see it .. With the prefinished oak floors I used a pad sander with additional weight on it. It takes a LOT longer. Started out with 36 then 60 then 100. Spent all day on about 500 sq ft. Vac and tacked got first coat down, then sanded first coat with well used 100 grit paper the following morning.