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Mortar joints in brick masonry wear out. After 80 to 100 years, natural weathering erodes the mortar, especially soft lime mortar found in historic masonry. Stress from structural movement cracks the joints, letting in water, and eventually freeze-thaw cycles break down the mortar. You cannot reverse the aging process—only renew the outer layer by repointing. A repointing job should last for another 100 years, but some jobs last only a year or two. Why? Often, the mortar is too strong. When it comes to early brick masonry, stronger is not necessarily better. Cement vs. Lime Repointing jobs on historic buildings often fail because there are fundamental differences between modern and historic masonry. Setting time. When a wall is laid up with today's cement