One of our vanity doors is in very bad shape after a leak some time ago. Now I'm trying to save it if possible. I've managed to sand away the very bad swells
However the bottom feels rather fluffy.
Can I just use any undercoat and paint it with any interior paint?
Any advice appreciated.
Best Answer
Everyone has already noted in the comments how and why MDF is not a good material to use around water or moisture and that you'll likely have future issues so that is not addressed in this answer. This answer is for the case that you still wish to go forward with your work, perhaps as a temporary fix.
Because water is a no-go it is necessary to use an oil, alcohol, or lacquer based primer first and then, after sealing, you can use latex water based paint as desired.
Here is a couple of articles with other related information that might helpful