Out here in the Arizona desert, people assume masonry problems come from heat. They come from the mortar, same as everywhere else, the sun just hides it longer because things dry out fast between our monsoon soakings. Mortar is the sacrificial part of any masonry wall; it is meant to wear before the brick or block does. Knowing how to read it is the difference between a cheap repointing job now and a structural repair later.
Mortar is supposed to be the weak link
This surprises homeowners: mortar is designed to be softer than the units it holds. That way the mortar takes the stress of movement and weathering and can be replaced, while the expensive brick or stone stays protected. When people use a mortar that is harder than the brick, usually modern Portland-heavy mixes on old soft brick, the brick becomes the sacrificial part instead, and it spalls. So “failed mortar” is partly normal wear; the question is how far it has gone.
The signs, from minor to serious
Here is the progression I check, roughly in order of urgency:
- Powdering or sandy joints. Rub the joint; if it sheds sand, the binder is spent.
- Receding joints. Mortar has weathered back behind the face of the brick, leaving a shelf that catches water.
- Cracked or crumbling mortar you can pick out with a screwdriver or even a fingernail.
- Gaps and missing sections where mortar has fallen out entirely and you can see daylight or feel a void.
- Loose units. Brick or block that shifts when pushed, this is past cosmetic and into structural.
Once you see receding or missing mortar, water is getting into the wall, and stair-step cracking often follows, the pattern I break down in spotting structural cracks vs cosmetic cracks.
The screwdriver test
The simplest field check: take a flat screwdriver and press and scrape a joint. Sound mortar resists and stays put. Failed mortar gouges, crumbles, or falls away. Do this at a few spots around the wall, especially on the weather side and low near grade where water collects. If the joints are giving way in multiple places, the wall is telling you it is due for repointing.
What to do about it
The fix for failed mortar is repointing, raking out the bad mortar and packing in new, matched mortar, which I explain against the decorative technique in repointing vs tuckpointing. The critical part is matching the mortar to the wall, soft lime-based mortar on old soft brick, never a hard modern mix. The Brick Industry Association’s technical notes cover mortar assessment and matching through the Brick Industry Association. Catch failing joints early and repointing is routine maintenance; ignore them and water does the rest.
Where to look first, and how often
Mortar does not fail evenly across a wall, so knowing where to check saves time. Water drives most failure, so the joints that go first are the ones that stay wettest: the weather side of the house, anything under a leaking gutter or downspout, the low courses near grade where splashback and rising damp work on them, and the joints around windows, sills, and copings where water concentrates. Chimneys above the roofline take the worst of the weather and are worth a look every time you are up there. I tell homeowners to walk their masonry once a year, ideally in spring after the wet season has done its work, and run the screwdriver test at those high-risk spots rather than randomly. In the desert I add a check after monsoon season, since that is when a year’s worth of water arrives at once. Catching a few soft joints early turns repointing into a small, scheduled job instead of an emergency, and it keeps water out of the wall before it can reach the brick faces and cause the spalling that is far more expensive to fix.
Frequently asked questions
How do I know if my mortar needs repointing? Check the joints: powdery, sandy, cracked, receding, or missing mortar all signal failure, as do loose bricks. The screwdriver test, scraping a joint to see if it holds or crumbles, is a quick field check. Failing joints in multiple spots mean it is time to repoint.
Is crumbling mortar a serious problem? It becomes serious once joints recede or open up, because water then enters the wall and accelerates damage, and loose units mean the wall is losing integrity. Caught early as surface wear, it is routine maintenance; left long enough, it leads to structural repair.
Why is my brick cracking instead of the mortar? Usually because someone used mortar harder than the brick, often a modern Portland mix on old soft brick. Mortar is supposed to be the softer, sacrificial element. When it is too hard, the brick takes the stress and spalls instead. Matching mortar strength to the brick prevents this. Moisture arriving from inside the wall does the same damage, which is why a Tarrytown HVAC contractor gets called when a flue or vent turns out to be the source.