Masonry air leaks
Masonry materials must be airtight and have airtight joints between the building assemblies to function as air barriers. Masonry roofs, walls, and floors may or may not be airtight. For example, concrete block isn’t itself airtight. Joints between masonry blocks may leak air. Also, cavities in masonry blocks may connect to air-permeable soil, floor cavities, attics, and roof cavities to conditioned areas of the building. Effective air sealing requires sealing leaks in the block and filling empty block cavities.
For buildings built with only masonry materials, these materials should somehow form a continuous air barrier. Masonry work requires knowledge and attention to detail for new construction, repair, and retrofit air sealing. Mortar, plaster, and stucco are air sealants. Workers who repair concrete, masonry block, plaster, and stucco may achieve significant reductions in air leakage and increases in building durability.
There is no substitute for knowledge and experience when repairing and air-sealing masonry materials. If the repair must strengthen the building against earthquakes, a structural engineer with expertise in masonry should advise the building owner and the masonry contractor. With the right specifications and workmanship, a weakened ancient building could last another century or more and function as an air barrier.
Masonry air sealing and repair
Air-sealing and structural strengthening are complementary renovations to masonry buildings. Strengthening existing masonry buildings is a priority for many countries, especially those threatened by earthquakes and windstorms. Masonry buildings lose strength over time from damage by moisture, movement, and wind. Repair crews, throughout the world, install innovative masonry assemblies to the exterior of existing unreinforced masonry walls and reinforced concrete walls and beams. If these crews understand the importance of air-sealing, they are careful to leave no cracks or openings in their renovations.
Know the composition of the masonry materials you repair. Repair materials may be incompatible to original materials, causing repair failure. The repair material’s composition, water-vapor permeability, water porosity should be compatible to the existing masonry. For example, use lime mortar to patch or repoint lime mortar between bricks and blocks. Use cement-based mortar or stucco to patch existing cement-based masonry.
Surface preparation is very important to air-sealing existing masonry materials and may include pressure-washing, sand-blasting, and acid washing. Repair materials may fail to bond to the original materials because of inadequate preparation.
You can install a variety of coatings to porous masonry materials that function as air barriers, vapor retarders, and WRBs, depending on your climate and your goals for the building.
Masonry air-sealing and repair materials
Consider these materials and methods for repairing and air-sealing masonry assemblies.
- Masonry bonding agents of various formulations (depending on required strength) that you paint onto prepared surfaces and into cracks. Masons also add these liquid bonding agents to mortar.
- Glass, steel, carbon, basalt, and plastic fabrics applied in stucco layers to strengthen walls, columns, beams, and vaults in a process called jacketing.
- Polymer fibers to reinforce mortar and stucco to jacket deteriorated masonry wall.
- Traditional mixtures of lime, water, and sand with or without portland cement, for patching mortar, stucco, and interior plaster. Lime surface mixtures work well to match the texture of existing surfaces.
- Dry mixtures in bags that combine ingredients for specific purposes.
- Wet mixtures in buckets that combine ingredients for specific purposes.
- Backer rod or 1-part foam to fill large cracks and polyurethane caulk to seal the surface cracks.
- Masonry adhesives that may repair broken masonry block and brick better than common mortar.
Information taken from: Residential energy: Cost Savings and Comfort for Existing Buildings
For the latest ideas on masonry, read Masonry Magazine
For excellent demonstration videos on plastering, go to Kirk Giordono Plastering on YouTube