How can I remedy sags and runs on new paintwork?

This is usually caused by uneven paint application on broad, flat surfaces, or by over-applying on mouldings or rough-contoured surfaces. Also, failing to join up 'wet edges' before they have set can cause excessive film thickness, resulting in sagging and running. When the paint film is thoroughly dry rub down the sags/runs using wet and dry abrasive paper (or waterproof silicon carbide) together with warm water and detergent. To prevent sags/runs when painting broad, flat areas, work systematically and cross-brush each section into the next; finally using vertical strokes to gently lay off along the length of the surface.