Poly is not affected by alcohol or most other solvents, which is both good and bad depending on the the application. Test in an inconspicuous spot to be sure. Common sense says to cover the floors but they should be safe. Why not use shellac again when you finish the mantle? Someone may want to redo your work years from now which will be easy with shellac but next to impossible with poly.

Poly is usually unaffected by alcohol.

Poly is also quite hard and will craze----the tiny network of interconnecting cracks in a finish---when subjected to cycles of heat/cold like those that can occur on a mantle. Poly is so hard it chips easily when hit and repairing it is virtually impossible---the entire surface must be recoated.

Refinishing with shellac will be faster---you can recoat in 1/2 hour, where poly (oil based) needs 24 hours between coats. Water based poly needs four hours or more in most cases.

Or you could use varnish, but that needs the 24 hour dry time also.

Shellac and varnish can chip, but can be feather sanded and spot covered with a little smoothing with 0000 steel wool.

I normally don't comment, but read this a feel I must. The majority of WATERBORNE finishes and denatured alcohol , shellac thinner, everclear, etc., DO NOT PLAY WELL TOGETHER. A way to test is to throw a "soaked with denatured alcohol" on a waterborne polyurethane floor. UNFORTUNATELY,..it will probably melt itself into the floor. I wish it was different, but it's not. This is generally not true for waterborne epoxy finishes,. But is true for most single stage waterborne finishes. For oil based polyurethane, I don't ever recall having a problem using denatured alcohol or "goof off" from home depot...to remove latex paint spots.

I'm refinishing a GrandBanks interior. It's a satin finish on the wood. I sanded it, sprayed with alcohol to wipe down and it turned the finish cloudy white. What would that finish be??? I thought it was a polyurethane finish. Maybe it was waterbased polyurethane instead of oilbased?? ANy thoughts? Is oilbased polyurethan compatible with water based polyurethane??