The Danger of Bondcrete in Heritage Masonry
Limestone fretting due to use of a cement mortar
Over the years, I’ve seen extensive damage to heritage brick and limestone walls in Perth and Fremantle caused by sealants, particularly Bondcrete and other non-breathable paints.
Sealing heritage walls is never advisable because breathability is essential to the wall’s health, especially in managing rising damp and moisture issues. It often takes years for the damage caused by sealing walls to become apparent.
Initially, the surface may seem fine and intact, held together by the sealant. However, beneath the surface, moisture begins to build up, leading to the breakdown of the material into sandy pockets.
Other issues caused by sealants and non-breathable paints include:
Damp issues: Moisture becomes trapped within the walls, unable to escape.
Sweating: The walls can “sweat” moisture, leading to further deterioration.
Fretting: Damage to the stone or brick beneath the sealant.
Brick and stone decay: The materials deteriorate more rapidly.
Unnatural-looking tuckpointing: The sealant can create an artificial appearance.
Unnatural sheen: The surface takes on an undesirable, glossy finish.
Why Do People Seal Heritage Walls?
The primary reason people seal heritage walls is the false belief that it will protect the wall from further deterioration. This misconception often arises from a lack of education on the subject, a desire for a quick fix, or reliance on unskilled tradesmen. Some also mistakenly believe that sealing will extend the life of tuckpointing.
We are frequently contacted by clients who want to seal internal heritage feature walls, frustrated by the dusting and shedding that occurs, as well as the constant cleaning of floors and furniture beneath. While all heritage walls, particularly limestone rubble, will shed a small amount of dust, this is minimal and typically not noticeable on external walls. However, when it’s an internal feature wall in a kitchen or living room, it understandably becomes a concern.
Alternatives to Sealing or Painting Limestone
Instead of sealing or painting limestone, there are several effective alternatives:
Heritage breathable lime washes: These allow the wall to remain breathable while providing a protective finish.
Proper restoration: This includes cleaning limestone surfaces of loose dust and solidifying the stone faces.
Repointing mortar joints: Using a mortar with good compression to form a protective “skin” over the lime mortar.
Modern breathable sealants: These alternatives allow moisture to escape while still offering some protection.
Once a non-breathable sealant is applied, it is challenging to remove during the restoration process. However, we’ve had success in removing it by applying boiling water under light pressure.
If a heritage wall, whether brick or limestone, is restored correctly, it does not need to be sealed.
While Bondcrete and non-breathable paints have their place in the building industry as adhesives, they should not be used for sealing or painting heritage walls.
If you need more information, feel free to contact us.
Regal Heritage Restoration’s Jake applying breathable sealant to a limestone wall.