Is it normal for old mortar to be softer than new mortar?

Lime-based mortar stays somewhat flexible even after it cures, which lets it absorb small amounts of movement in a wall without cracking the brick. Modern Portland cement mortar cures much harder and more rigid. Both can be correct choices, but they're not interchangeable, and the mortar is supposed to be softer than the brick it's holding together, not the other way around.

The real risk shows up during repairs. A common mistake is repointing an old lime-mortar wall with modern hard Portland cement mortar because it seems stronger. It isn't a fair trade: hard mortar doesn't flex with the wall, so instead of the mortar absorbing stress and wearing over the decades, that stress gets pushed into the brick faces, which can crack or spall the brick itself, a much more expensive problem than crumbling mortar ever was.

When Chelo's looks at old mortar, the question isn't just whether it feels soft, it's whether that softness is normal for the mix and age of the house or whether the mortar has actually failed. Matching the replacement mortar to the original type, rather than defaulting to whatever's strongest, is what keeps an older wall performing the way it was built to.

This is one reason a walk-through by someone who works on older masonry regularly matters more than a general contractor guessing at it. Telling normal lime softness apart from actual mortar failure by feel takes some experience, and using the wrong mix on a repair is a mistake that doesn't show up as a problem right away, it shows up as brick damage a few winters later.

• Softer mortar is common and often correct on homes built before roughly the mid-1900s
• Lime-heavy mixes flex more but wear faster than modern Portland cement mortar
• Hard modern mortar against old brick pushes stress into the brick, not the joint
• A scratch test can help tell normal softness apart from mortar that's failed
• Matching the original mortar type matters as much as matching the brick