Why Using Internal Surface Filler on External Timber Cills Is a Costly Mistake
Timber window cill
External timber window cills take a beating. From driving rain and winter frosts to harsh summer UV, they face constant exposure to the elements. Because of this, repairs must be carried out with products designed specifically for outdoor use. Yet one of the most common, and costly, DIY mistakes is using an internal surface filler on these external components.
At first glance, an interior filler might seem harmless: it spreads easily, sands nicely, and gives a smooth surface ready for paint. But beneath that perfect-looking finish is a repair that’s destined to fail.