Tuff Window Sills

They are called Stone Jambs and Stone Mullions!

Jambs stones are an integral part of any window or door surround. They are the 'side pillars' that stretch from the cill to the head. Jambs are structural stones giving support the heads (or lintels) and also to the window frame which sits inside them.

Mullions are the vertical stone sections that separate two window units using the same head and cill. A transom is the horizontal stone that separates two window units.

Window Surrounds can comprise of cills, heads, jambs and mullions. We have two standard styles – plain and chamfered. Jambs are manufactured with fixing anchors (dovetail slots). For tall windows, jambs and mullions are connected via stainless steel dowels.

Painting stone is not recommended and will be a factor in the rotting process although in my opinion, not the main cause. The main cause is water and although it keeps us alive it is the enemy when it comes to stone mullions.

The mullions are creating a cold bridge in a warm room that has a high moisture content. As soon as this warm moisture comes into contact with the cold stone mullion, the water condenses onto the stone. Clean off the mould with a solution of warm water and bleach.

A 2cm thick marble window sill also performs the same function, but it should be preferred to be at least 3 cm in terms of aesthetics.

Start by measuring the width and depth of the framing on the inside. The sill should overhang the front edge of the window frame at least 3/4 inch, but feel free to add up to 4 or more inches to the depth, depending on how much overhang in front you desire.