Walls, doors and windows are where a house shows its problems first: a crack, a draught, a patch of damp or a door that has stopped shutting.
Filling a hole properly
The common mistake is filling flush. Filler shrinks as it dries, so a flush fill leaves a dip.
- Clean the hole out and remove anything loose.
- Press filler in so it is slightly proud of the surface.
- Let it dry fully. Rushing this is why filler cracks.
- Sand back flat with fine paper on a block, not your fingers, which leaves a hollow.
- Prime the patch before painting, or it will drink the paint and show through.
Anything bigger than a fist, or on plasterboard, wants a patch rather than filler on its own.
Draughts
Draughtproofing is the cheapest heating improvement there is and the most often skipped. The usual culprits, in order: letterbox, keyholes, under external doors, sash window gaps, unused chimneys, and the gap where floorboards meet skirting.
Do not block permanent ventilation: air bricks, trickle vents, and any vent serving a fuel burning appliance. Sealing those is how you cause damp, or worse. See heating, damp and energy.
Condensation on glass
Water on the inside of a window is warm moist air meeting cold glass, not a leak. Between the panes of a double glazed unit means the seal has failed and the unit needs replacing; nothing you do to the surface will help.
Doors that stick
Wood swells in damp weather, so a door that sticks in winter and not in summer needs the damp addressing rather than planing. Plane it in January and you will have a gap in July.