Live plant tissue is exposed and vulnerable to infection when cut. A good sealer must be applied to the wound to prevent such infection as well as cracking due to drying out. Preventing the cut from drying out will ensure that the live cambium/tissue of the tree will be able to heal the scar quickly and as smoothly as possible so ensure the paste overlaps the cut by 1mm or more.
In this range of pastes there are 3 options: