Facade Plans Post 3 – How NOT to Restore Historic Masonry

Then comes restoring the brick, and this job is scary. I’m going to take the paint off my brick. Many sources recommend avoiding this as it can damage the substrate, but you saw what the paint looks like on my house. For further reading, I suggest this piece from the National Park Service, the preservation guidelines for Boston’s Beacon Hill neighborhood, and the New York and Philadelphia Rowhouse Manuals.

The problem is that traditional bricks have a durable outer layer from being kiln fired. Inside of that they’re much softer and it’s important  not to take that off. So…

What you really should never do is of course what everyone does. Scrub pointing, or covering over the mortar joints with new mortar without removing the old. This alters the look of the brick and it doesn’t hold up.

Don’t power wash the brick with high pressure. Traditional bricks were kiln fired and you could take off the outer later, which is the most durable part. And NEVER sandblast historic masonry. This can wear away the surface badly, altering its appearance and shortening its life. I encountered this poor facade on tony Spruce Street. I would have thought it was some kind of rustic 1920’s brick except for that little square that was once covered, revealing the same pressed brick as I have. Also pictured: scrub pointing, paint.

NEVER use dry heat like a heat gun. This can drive paint deeper into the masonry and make permanent stains. Plus, it doesn’t work well on masonry.

NEVER clean or strip masonry when there’s any risk of frost as any extra moisture that absorbed could freeze, expand, and cause the masonry to spall.

Avoid driving too much water into the masonry even in mild weather as it’s weaker when wet. Repointing before cleaning the surface is a good move, but you can also temporarily caulk the joints and repoint later.

Don’t sand or grind the surface.

Avoid strong acids (Hydrochloric/Muriatic) and alkaline (lye) products and only use in very limited applications.

Don’t use acidic cleaners on acid sensitive stone like marble. (That’s me!)

Don’t expect surfaces to look brand new. Some patina may be desirable and vigorous efforts to remove troublesome stains or residual paint can damage the substrate.

So what can you do? Use the gentlest means possible. Low pressure washing, hand scrubbing, washing with a non-ionic detergent, some mild acid and alkaline cleaners, steam cleaning, and dangerous chemical solvents can all be effective. Test in an inconspicuous area (which I don’t have) preferably a full year before proceeding, but at least a month.

And when I repoint I must not use modern masonry techniques. My house is made of traditional clay bricks with lime mortar. Modern mortars are harder than this kind of bricks, so if the wall shifts, the bricks fail instead of the joints. Some preservationists recommend only using lime while others specify a soft mortar made with lime and Portland cement.

My façade is pressed brick, which is very smooth and uniform with very thin mortar joints. The mortar is washed or colored red to match the bricks. Scrub pointing is putting a false wider mortar joint over the real ones. This kind of halfassed job eventually pops off and until it does, it fakes the look of inferior and historically incorrect masonry.

And what about that damaged area?

I think I should use a water resistant coating here. These are formulated to let water vapors out but prevent liquid water from getting in. Never use a waterproof coating that traps both. And even the best of these products can do more harm than good, but it sounds like treating the damaged areas only could help preserve it. Or if I pick the wrong one it could help destroy it.

So this will be fun right?