What Mortar Belongs on Old Syracuse Brick

Softer mortar than your brick, never harder. National Park Service Preservation Brief 2 states the rule directly: repointing mortar should be more vapor permeable and softer in compressive strength than the masonry units around it, because the joint is the part of the wall that is meant to give way. So the question worth asking anyone who quotes for repointing is which mortar type they will use, by letter, and how they know it is softer than your brick.

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Why the joint is supposed to be the weak part of the wall

The mortar is the part of a brick wall you are allowed to lose, and that is deliberate. National Park Service Preservation Brief 2 sets four criteria for a repointing mortar, and two of them never show on a finished joint: the new mortar has to be more vapor permeable and softer, measured in compressive strength, than the brick, and no harder and no less permeable than the mortar it replaces. The reason is where stress goes. A wall moves with temperature, with moisture and with settlement, and that movement has to be absorbed somewhere. When the mortar is the softer material it absorbs it, and the worst outcome is a hairline crack in a joint, which can be raked out and repointed. When the mortar is stronger than the brick, the Brief says the stress is relieved through the masonry units instead, and the result is cracking and spalling that cannot be repaired easily. That is the whole argument in one line: mortar can be replaced as many times as a wall needs it, and a brick face cannot be put back.

The second way a hard joint does damage: it moves the water

Stress is only half of it. Historically a mortar joint worked as a bedding material, closer to an expansion joint than to glue, and moisture in the wall left through the joints rather than through the masonry units. High lime mortars are more permeable than denser cement mortars, so when a joint is replaced with something dense the water has to find another exit, and the only one left is the face of the brick. As that water evaporates it deposits soluble salts, and salt crystallization within a masonry unit creates pressure that can spall or delaminate the outer surface. The National Park Service publishes a photograph of the finished result and captions it plainly: hard portland cement mortar less permeable than the soft bricks, moisture unable to evaporate through the joint that was supposed to be sacrificial, and water pressure that eventually popped the surface off the bricks. Its page on common problems with brick masonry is blunter still, and worth quoting to anyone who thinks this is a detail. More damage is done to historic brick buildings with improper pointing than with almost any other treatment, and the damage is not only cosmetic.

The white powder on your brick is a symptom, not a fault

Efflorescence, the chalky white bloom that shows up on brick and on joints, is the wall telling you that water is moving through it and evaporating on the outside. That is information rather than a defect. Preservation Brief 2 is specific about the difference: soluble salts deposited on the surface as efflorescence are usually relatively harmless, and it is subflorescence, the same salts crystallizing below the surface inside the unit, that creates the pressure which pops a brick face off. So a bloom you can brush away does not mean your wall needs work, and it very much does not mean your wall needs sealing. What it is worth doing is finding where the water is arriving from, because a gutter joint, a downspout outlet, a missing chimney cap or an open joint above the affected area explains most cases. If the powder keeps returning to the same patch after a dry spell, that patch is the one worth a closer look.

Which mortar type, and what the letters actually mean

Mortar types are letters, and you should be able to say the letter you want out loud. Preservation Brief 2 lists them in decreasing order of approximate strength: Type M at 2,500 psi, Type S at 1,800 psi, Type N at 750 psi, Type O at 350 psi and Type K at 75 psi, the letters taken from the words MASON WORK using every other letter. Proportions are always given in the order cement, lime, sand, so a Type O is one to two to nine. There is one wrinkle you should hear from us rather than discover in an argument: the Brief lists five types including K, while the Brick Industry Association, reporting current ASTM C270, lists four, M, S, N and O, with K no longer among them. Both are accurate as published and we have left the discrepancy visible instead of tidying it away. For ordinary modern brickwork the Brick Industry Association recommends Type N for normal use, including most veneer. For soft old brick the direction of travel is downward from there, toward O, and where exactly it lands is a decision for whoever has looked at your actual wall.

Why the bag from the hardware store is the wrong bag

The preblended mix sold as masonry cement is the easiest way to get this wrong, and it sits on the shelf of every hardware store. Preservation Brief 2 records what it is: a product introduced in the 1930s to hasten and simplify a mason's work, containing a large amount of portland cement along with ground limestone and other workability agents including air-entraining agents. Because masonry cements are not required to contain hydrated lime and generally do not contain it, the Brief states that they produce high strength mortars that can damage historic masonry, and that they are generally not recommended for use on historic masonry buildings. This is not a fussy preservation preference. It is the same physics as the rest of this page, arriving in a bag that is quick to mix and looks entirely normal in a struck joint. Ask what is going into the mixer, and ask whether the lime is coming out of a bag of hydrated lime or is being taken on trust.

Matching the color is the half of the job that everybody does

Every mason in this market will offer to match the color, the texture and the joint profile, and they are right to offer it. Preservation Brief 2 explains why it works: the most useful thing a laboratory analysis of an old mortar produces is identification of the sand by gradation and color, because sand is the largest ingredient by volume, and that is what allows color and texture to be matched with some accuracy. The same Brief warns against writing a specification from laboratory analysis alone, because several things that decide performance cannot be recovered in a laboratory, among them the original water content, the rate of curing, the weather during construction and the condition of the sand. So appearance is a solved problem, and it is the visible half. Strength and permeability are the invisible half, they decide whether your brick is still there in twenty years, and almost nobody in this market advertises them at all. That asymmetry is the reason this page exists.

When you can leave it alone, and how to check with a screwdriver

Plenty of old joints look worse than they are, and the check costs nothing but a screwdriver. Preservation Brief 2 has old mortar cut back to a minimum of two to two and a half times the width of the joint, which for most brick joints means approximately half an inch to one inch, with any loose or disintegrated mortar beyond that depth also removed. Turn that around and you have a homeowner's test. Press the point of a screwdriver into a joint and drag it. If the point skates off and nothing comes away, the joint is doing its job, and hairline cracking with nothing loose can genuinely wait. If you can pick mortar out to something like half an inch with hand pressure, that section has already failed and water is getting behind it. This is a rough check on a patch you can reach, not a verdict on a wall, and it will tell you nothing about the chimney or the parapet you cannot get to. What it will tell you is whether you are looking at a job for this year or a job to keep an eye on, and that is most of what people want to know before they call anyone.

Why this bites harder in the city than out in Clay

The mortar mistake only matters where the brick is soft, and soft means old. The City of Syracuse has 67,601 housing units at a median year of construction of 1948, with 43.1 percent built in 1939 or earlier and 85.5 percent before 1980. That is a very large body of exactly the masonry a hard joint ruins. The Town of Clay is the mirror image: 26,282 units, a median year of 1978, only 3.2 percent built in 1939 or earlier and only 16.0 percent before 1960, with Cicero close behind it. In those towns the likely masonry problems are modern brick veneer details rather than mortar compatibility, and telling you otherwise would be selling you something. One honest caveat runs the other way as well: Preservation Brief 2 notes that many buildings put up in the first half of the twentieth century are now historic and may have been built with portland cement mortar originally, so old does not automatically mean lime. The question is still what is actually in your wall, and the answer still comes from looking at it. If you want that done, send us the address and what you are seeing.