I'm trying to restore a velux window frame that has become moldy and partially rotten. The window is 15 years old and has never had any attention. The sealant on the outside where the glass meets the metal casing had completely broken down so I have cleaned it out and applied a bead of black silicone. I'm hoping this will have solved the problem that caused the window frame to start to decay.
On the inside I have used wire wool to reduce the black parts. As I would like to get close to a factory finish I think I will need to use an electric sander to completely strip the outer coating before applying a few coats of varnish. (There are marks and what looks like fine mold specs that won't budge using the wire wool that are on the wooden frame that houses the window)
I am concerned that the window is not evenly aligned. (it's very tight at the bottom left and has a 6mm gap on the bottom right side) I am not sure if this compromises the seal to the outside.
I would appreciate any advice on how to go about restoring the window.
What varnish should be used? Do I need to use a product over the varnish such as polyurethane? Is the alignment a significant issue that will require further attention? (window currently locks fine, although it seems to push into the tight position when doing so) Is it likely that the outside seal on the glass being broken down caused the inside decay or could it be another issue that will need to be addressed before proceeding to sand it?
Any pointers would be very helpful.