Inside or outside the attention to detail is just the same, using quality materials for a lasting finish.
Damaged sills like this can be repaired by removing the rotten timber and applying a wood hardener before filling with an epoxy two pack filler.This gives a long lasting repair to a sill with a small amount of rot, especially after receiving a coat of Primer, then Undercoat and finally Gloss using high quality exterior paint which is formulated to last in such situations.
If the rot has gone too far the answer is to remove the sill altogether and replace it with a new piece of timber, making sure that it is well sealed into the existing frame.Once the sealant is cured it will receive a coat of Primer, then one of Undercoat and finally one of Gloss finish. We always use high quality exterior paint which is specially formulated to last outdoors.
All the other painted surfaces are scraped and sanded with the excess paint being removed from the glass. Any suspect areas of loose paint are removed using an electric heat gun.The bare timber is then Primed before the whole window receives one coat each of Undercoat and Gloss high quality exterior paint.