Cork flooring sealer problem

We have bought some cork tiles for our bathroom and fitted them OK, but when we used a polyurethane sealer to seal the tiles, the instructions said that this would dry in 4-6 hours, now 5 days later the sealer is still tacky. Is there anything that we can use to clean the tiles without damaging them, and what can we use instead to seal them that will be better?

Please help