A factory made door never expand. If it expands then you will have to observe the splits or cracks on the door suface which should be visible. Its a myth that everyone says door expands. Its not true. Instead, check with the frame whether it is seasoned timber with low moisture content. The frame which is not seasoned properly tries to absorb or release moisture and the frame is tagged to the wall only at two points on either side of the walls.
Using metal paste / Janatha paste or any waterproof chemical is the best option. To the door frames, apply 1 feet vertically from the bottom the metal paste and primer and paint them to give maximum protection. A carpenter generally trims the door and makes it to sit inside the door frame, then comes the painter and paints the door at front, back and sides. But no brush goes at the bottom of the door as the gap is very less, and everyone leaves the raw surface like that. Water spilled in toilets are absorbed from this bottom part and wood starts absorbing water and door becomes more thicker at the bottom day by day. Slowly it will Jam / block and will not sit properly in the frame and towerbolt / locking cannot be done. Hence, before fixing, bottom protection is 100% required.
