Which mortar should go into your old brick?

Say the letter out loud

Mortar is sold in types named M, S, N, O and K. They run from the hardest to the softest, and Preservation Brief 2 from the National Park Service lists them by approximate strength. Type M sits at 2,500 pounds per square inch, and Type K, the softest, at 75.

You do not need to memorize the numbers. You need to ask the mason to say a letter and give one reason for it. A mason who names a letter and a reason that mentions your brick is answering your question. A mason who says only that the mix will match is not.

Why softer is the right direction

The Park Service says a repointing mortar must be softer than the brick, more open to vapor than the brick, and no harder than the old mortar.

The idea is simple. A wall moves with the seasons, and something has to give. If the mortar gives, you rake it out and refill it. If the brick gives, you lose brick. Ask the mason to tell you which one they are protecting.

What a hard joint does to the brick face

Water moves out of a wall as vapor, and in an old wall it moves out through the joints. A dense joint blocks that path, so the water escapes through the brick face.

As it dries it leaves salts behind. The salts crystallize under the surface and press the face off in flakes, which is the damage the Park Service photographed in Brief 2. If your brick is flaking beside hard-looking joints, tell the mason before they quote.

Bagged mixes and what they hide

A bag from a home store can be masonry cement, which holds a lot of portland cement. Preservation guidance generally advises against it on old brick because it makes a hard mortar. Ask what is in the bag, and ask to see the label if you like.

The Brick Industry Association points to Type N for normal use on newer brick and veneer. That does not make it the answer for an old soft wall. Ask the mason why the type they chose suits your brick, not brick in general.

How your house's age changes the question

The City of Syracuse has a median build year of 1948, and brick of that age can be soft. Newer suburban houses may have harder brick or brick veneer, and the Census does not record wall types, so ask the mason to name yours.

Brief 2 also notes that some buildings put up in the early 1900s were laid with portland cement mortar from the start. So the mortar already in your wall may not be soft. Ask the mason how they tested it, and what they found.

A scrape test you can do yourself

Pick a hidden joint, such as one behind a shrub. Press a house key into it. Soft mortar gives up grit. Hard mortar barely marks, and the key skates off.

Do not treat that as a lab result. It is a prompt for a better conversation. Tell the mason what you did, and ask whether they agree and what the new mortar should be.

Matching the color is the second question

Many masons talk about color first, because color is what you see. The sand in the mix sets the color and the texture, and a good mason can match it closely. That is a fair thing to ask for, and it should come after the strength question, not before it.

A repair can look right and still be wrong for the wall. If the first words you hear are about color, ask the strength question out loud and see how the mason answers.

Depth and the tool matter as much as the mix

Preservation guidance puts the cut at two to two and a half joint widths, which on most brick walls works out to about half an inch to an inch. Shallower than that, and the new mortar has little to hold.

The same guidance warns that power saws and grinders in unskilled hands can be disastrous for soft brick, and that on thin joints they almost always break the brick edges. Ask the mason how deep and with what, and listen for a plain answer.

The honest answer is sometimes to wait

Not every joint needs work. A hairline crack in the mortar with nothing loose can be watched for a while. White powder on the surface is a sign that moisture is moving through the wall, and the water is the thing to find first.

If a mason tells you that everything must be done at once, ask which joints are worst and why the others cannot wait. A good answer ranks the work.

When the weather lets new mortar set

Mortar cures best in mild weather. In Syracuse that leaves a season, not a year. Ask each mason when they would do the work, and how they protect fresh joints from frost.

Antifreeze additives are not recommended, because they can leave salts in the wall. Ask what the mason uses instead, and book early enough that you are not squeezed into a cold week.

Questions to ask, in the order to ask them

1. Which mortar type will you use, and why?
2. What tells you it is softer than my brick?
3. How deep will you cut the old joints?
4. Which tool cuts them, and where?
5. Can I see a test patch before you do the wall?

Write the five answers beside each quote, and compare them before you compare the totals.

If you have already had work done

If an earlier mason repointed your wall, look at the joints now. Hard-looking joints beside flaking faces suggest the mix was stronger than the brick. Tell the next mason, and ask what they would change.

You do not need to blame anyone. You need to find out what is in the wall so the next repair does not repeat the problem. Ask for any paperwork from the earlier job, and keep it with your photographs.

What to put in writing

Ask that the contract name the mortar type, the proportions or the product, the joint depth and the tool that cuts the old joints. Ask for a test patch on a hidden section before the whole wall is done.

If a mason will not write down the type, you have learned something. Ask the next mason the same question.

Basis: NPS Technical Preservation Services, Preservation Brief 2 Brick Industry Association, Technical Notes on Brick Construction 8