I recently purchased a home which has a tongue and groove wood ceiling in a screen porch that had not been maintained over the past seven years. So it was restoration time.
The ceiling was untouched for years all though protected by the elements directly it still withstood moisture and no sun whatsoever.
Te process I choose for this restoration of the ceiling was:
As you can see by the pictures it is now protected for years to come and endure the weather all though no directly hot by rain or snow it does have to have a protective coat.
Tips for this project;