How to seal up gaps?

ChilliBob

Only use caulk or frame sealant if you're going to paint over it, otherwise it'll be a dust magnet!

Depends what the aim is.. You can get this plastic strip stuff that folds if half, and you can get foam you squash and let it fill the gap. 

Unless you have experience, I suspect expanding foam will be tricky. Also, one finished and trimmed you'd need to put some filler over it or it'd look a bit naff. 

chris_n

ThisIsWeird said:

Blackstar, is this mainly for aesthetic reasons, or to blocks draughts?

For aesths or both, something I've done in the past is to cap the existing cast skirting using architrave and MDF - 4mm MDF should be ok, provided you use enough filling adhesive behind it. But i'd still seal the gaps first using cheap frame sealant or caulk.

This is the best answer, fill the gaps first then use low expansion foam adhesive to attach the MDF / profile.