Why Timber Stair Treads Turn Grey or Black (and How to Fix It)

This is the most common one. The varnish has worn through on the walking line, so dirt and mopping water get into bare timber and turn it grey. The fix is a full sanding back to clean wood and fresh varnish.

Black marks are usually water reacting with the tannins in the timber: from plant pots, wet umbrellas, a leaking window or pet urine. Light stains can be bleached after sanding; deep ones go through the wood, so those pieces are replaced.

Sunlight through windows and skylights bleaches timber over time, so the steps it reaches are lighter than the rest. After sanding, stain evens the colour out. UV film on the glass helps stop it coming back.

Older oil-based varnishes turn amber with age. Sanding off the old finish and using a non-yellowing water-based or PU varnish keeps the natural colour of the wood.