Repairing Stone Mullions

Possible causes of damage to stone mullions

Water infiltration is one of the major causes of damage to stone mullions, this can occur as a result of the following factors.

Most stone has a ‘seam’ or ‘grain’ and if made and fitted incorrectly into the build, water and frost will permeate into the stone causing it to blow, whilst wind and rain will etch at the surface.

Some stone ullions have metal rods inserted through their core for added structural integrity. Often these rods are made from ferrous metals, such as iron or steel. Ferrous metals are more susceptible to rust and corrosion. As such, these rods may react with moisture present within the stone, beginning to rust and expand. This build up of pressure over time damages and cracks the surrounding stone.

More often than not, however, the stone will deteriorate as a result of old and rusting steel casements. As steel is a ferrous metal, the screws can rust and expand, cracking the metal windows. A build up of water over a long period of time causes the stone to burst allowing further water ingress, which in turn leads to greater long term damage.

Methods for repairing stone mullions

Every case should be judged on its own merit and it has to be said that for some, there is a beauty in seeing aged old flaked stone – a clear indicator as to the integrity of the building and forming part of the building’s history. In these instances, less intrusive repair options may include filling with lime mortar which is mixed with stone dust. Cracked mullions and transoms can be resin filled and re-built with supporting dowels.

However, if you believe that your windows have seen better days, or are tackling larger areas of deterioration, sections of stone may be totally replaced with matching stone from a quarry.

It may be time to invest in replacement windows. Real bronze is a non-ferrous metal, meaning it is not susceptible to rust and corrosion which, in turn, helps towards preventing damage to stone mullions. This combined with its natural patina and signature rich warmth make it the perfect fit for stone surrounds, whether historic, refurbished, or brand new.

Methods for repairing stone mullions

Regularly inspecting stone mullions for signs of cracking, weathering, and moisture infiltration can help identify issues early, allowing for intervention before damage becomes severe.

Ensuring proper water drainage around windows and mullions is crucial in preventing moisture-related damage. Gutters and downspouts should be well-maintained to keep water away from vulnerable areas.

The growth of moss, algae, and lichen should be controlled around stone mullions. Their presence can trap moisture against the stone leading to surface damage.

Ask an expert first

It should be noted that any assessments or repair work carried out should be performed by an expert in this field. They will be able to advise you on the options available for your particular situation and make the necessary recommendations. Companies awarded The Heritage Gold Card are names to be trusted.