How to protect a painted wooden table if you wanted to put it outside
Suggested Project Book
Seal the table with an outdoor polyurethane
Polyurethane. Might take multiple coats so go slowly with thin layers and letting it dry in between each.
Polyurethane is the right idea. Use High Gloss as it has a harder finish. Then if you prefer a dull or soft finish, make your top coat with satin Polyurethane. You will need 2 coats of the high gloss and 1 of the satin. Store inside during winter/snow months. Ours lasted for over 20 years doing that.