The job a sill does
A stone sill is more than decoration. It throws rainwater clear of the wall beneath the window, usually with a slight slope and a projecting drip groove on the underside. When the stone wears, cracks or the drip is lost, water runs down the wall, stains the brickwork and may enter the building around the window.
Typical faults
- Surface erosion, particularly on soft sandstones
- Cracks, often caused by rusting iron fixings or settlement
- Sills that have been painted or sealed in a way that traps moisture
- Hard cement repairs that break away or crack the stone
- Blocked or missing drip grooves
- Failed joints between sill and frame
Repair or replace?
Where the stone is mostly sound, repair is often possible. Options include cutting out the damaged portion and fitting a new piece of matching stone, known as an indent, or using a suitable lime-based repair mortar for smaller areas. If the sill is badly cracked, split or heavily eroded, replacement in matching stone is the more durable route. The choice depends on the stone type, how much has failed, and the character of the building.
Matching stone
Many Newcastle and Tynemouth buildings use local sandstone, and different stones weather differently. Using the wrong stone can accelerate decay or look out of place, so identifying and matching the stone is part of the work.
How we do it
We check the window and surrounding masonry, since a failing sill often goes along with damp or rotten frame timber. The sill is then carefully removed, the bed is cleaned and prepared, and the new or repaired sill is set in a suitable mortar with correct falls. Joints are pointed, and any adjoining brick or stone is repaired. Where a sill supports a masonry mullion, additional care is needed.
For related work, see decorative stone cornice repairs and lime repointing. In conservation areas or on listed buildings, check consent requirements with the Planning Portal.
Frequently asked questions
Can a worn stone sill be repaired without replacing it?
Often, yes. Minor erosion can be repaired with compatible mortar, and damaged sections can be indented with new stone. Severely cracked or decayed sills are better replaced.
Why is water getting in around my window?
A damaged sill, missing drip groove, cracked joints or a failed seal to the frame can all let water in. We check the whole window opening, not just the sill, to find the cause.
