A few common home repair products to avoid on old buildings.

DO NOT USE

-Pure Portland Cement Mortar-

The strength and inflexibility of common portland cement mortar will eventually damage softer, more porous bricks, stones and the lime-based bedding mortars. The regular use of portland cement began in the early 20th century when simultaneously bricks were manufactured to be harder and less porous. Earlier buildings require softer, more permeable mortars because the brick and stone itself is generally softer and more permeable than portland cement mortar. Pointing mortar needs to be weaker than the brick and stone it surrounds, so when under stress and something needs to break, it is the mortar that breaks and not the brick or stone it adheres to. A softer mortar functions so well in old buildings because it IS NOT STRONGER than the masonry units it holds and supports. After about 30-50 years of slow deterioration to the face of the lime mortar joints, the pointing mortar will need to be replaced, or at lease repaired, under normal conditions. 100% lime mortar comes in a variety of strengths to best suite the application and is always a safer choice for pointing old buildings than portland cement.

Lime-based mortar is slightly flexible so it can withstand a small amount of movement, can self-heal minor cracking, and it allows water vapor to escape easily through the wall.

DO NOT USE

-Impermeable Layer in Wall Assemblies-

The damage starts when excess water builds up behind waterproof coatings, foil backings, spray foam, plastic sheeting, etc. where the water is stopped and cannot easily dry out. Old wall systems want to "breathe", meaning allow water vapor to pass through them, as its a natural process with differences in humidity, air pressure, and temperature between the inside and outside of a building. Walls in older buildings should be repaired/renovated in ways allowing this natural process to occur. When an impermeable plastic, foil or foam is installed, the water still travels through the rest of the wall until it hits that impermeable surface, where it builds moisture. The kind of damage will depend on where the impermeable surface is, but trapping water always leads to damage.

In fact, research has shown that waterproofing is misunderstood in general and impermeable coatings, linings, and fillers harm many newer buildings as well.

DO NOT USE

-So Many Adhesives-

Adhesive products are a huge industry and there are tons of options at the local hardware store. But the unnecessary use of adhesives to fasten materials can make future repairs more difficult and costly. New flooring glued down over older wood floors means removal will likely destroy the older floorboards underneath, even if they are in great shape. Adhesives gluing brick veneers to plaster walls make their removal slow and painful when the the fad has passed. The confusion begins with the way adhesives are recommended and marketed for so many product installations. The assumption in modern thinking is that when that thing is removed, it will be time for everything around it to be demo'd and rebuilt new. Preservation works against that kind of throw-away culture. Preservation is about maintaining something of quality for as long as possible. If you want to preserve something, it needs to be designed for maintenance to create longevity.

Adhesives, especially epoxies, play an important role in repairing older woodwork with limited damage. Many repairs to old windows and doors would not be possible without modern adhesives. The best wood repairs only use adhesives to attach new material onto a damaged piece, Adhesives shouldn't be substituted for fasteners or joinery when maintenance and longevity are the goals.