Chimney Brick: Types, Age and Matching Old Brick

Chimney Academy · How it works · Updated October 2026

Why two red bricks can behave very differently

Brick is fired clay, and the firing is what sets its personality. Clay that is heated long enough to begin partly fusing, which manufacturers call vitrification, turns out dense, strong and low in water absorption. Clay that is pulled from the kiln earlier stays more porous and softer. The Brick Industry Association explains that for a given clay and forming method, higher firing temperature lowers absorption and raises strength, and that firing temperature also shifts color toward darker tones.

That last point is why color is a poor guide. A pale brick can be hard and a deep red one can be soft, depending on the clay and the kiln. Two bricks that look identical from the ground may differ in how much water they soak up, and water is what damages masonry in a New Jersey winter. Water gets into the face, freezes, expands, and pushes a thin layer of the surface off. The full story of that failure is in our guide to spalling brick and freeze damage.

Forming method adds another layer. Most American brick is made by pushing stiff clay through a die and cutting it. Others are pressed into molds from wetter or drier clay, which is how many older, softer-edged bricks and handmade-look bricks are produced. None of these methods is automatically better, but each leaves different surface texture and different absorption, which is why a repair brick has to be chosen, not just grabbed.

How brick is graded for weather

Industry standards sort brick into weathering grades. The terms you may see on a spec sheet or a supplier’s list are SW, MW and NW, short for severe, moderate and negligible weathering. Facing brick, the kind used where appearance matters, is made in the first two grades. Building brick, used as hidden backing, also allows the third.

The grade comes from three measured properties: compressive strength, absorption after a five-hour boil, and a saturation ratio that compares cold-soak absorption to boiled absorption. The numbers are lower for severe-weathering brick than for moderate, which is the point. A chimney stack is about as exposed as masonry gets, with weather on all four faces and the top. It stands above the roof, takes wind-driven rain, and cycles through freezing constantly in a cold climate.

If a supplier cannot tell you the grade or the absorption of a brick, treat that as information. Unlabeled brick is a gamble for an exposed stack.

Age, soft brick and what it means for your chimney

Older New Jersey homes often have brick that was made locally and fired unevenly in older kilns. Within a single batch, bricks nearer the heat were fired hard, and those on the cooler edges came out underfired. Masons have long called the pale, soft, orange-pink ones salmon brick. They absorb water readily and are the first to flake when they are exposed on a chimney face.

So an old stack is often a mix. Some bricks look nearly new after a century. Others have lost their faces. That pattern does not necessarily mean the whole chimney is failing. It can mean a handful of weak units were placed where the weather hits hardest. A mason can sort that out by looking at where the damage clusters. Our overview of chimneys in older New Jersey homes covers more of what to expect with age.

One more age-related point. Old brick was usually laid in softer lime-based mortar. Modern mortar can be harder than the brick itself, which pushes stress into the brick instead of the joint. The mortar question deserves its own look, and the masonry repair and repointing service page describes how joints are worked on.

Salvaged brick: what it solves and what it does not

Reclaimed brick is attractive for one reason: it looks right next to old work. The Brick Industry Association’s technical note on salvaged brick is blunt about the trade-offs, though. Its main points:

• Salvaged lots mix hard-burned brick with underfired ones, so the properties of any pile are unpredictable.
• Old mortar clings to reused brick and is nearly impossible to clean completely, which weakens the bond with new mortar.
• Poorly bonded joints are where water gets in, so walls built from reclaimed brick can leak more and carry load less well.
• Soft salvaged brick can spall, flake and crack in freeze and thaw cycles when exposed to weather.
• Reclaimed brick cannot be given a specified grade or color blend the way new brick can.

The same note advises against using brick salvaged from chimneys and recommends avoiding reclaimed brick on surfaces with high moisture exposure. It also points out that early savings can disappear when disintegrated units must be replaced later.

None of this means salvaged brick is never appropriate. A small patch on a protected wall is different from the top courses of a stack. It does mean the choice should be made with the exposure in mind, and with a clear idea of what to do if a patch starts to fail.

What to match, and what matters more than color

Color is also the property most likely to change. Fresh brick sits beside weathered brick and looks different for years. Masons often set a few sample units, let the person see them, and accept that a repair will blend over time instead of disappearing on day one.

Before any brick is replaced

A good repair plan starts by finding why the brick failed. If a bad crown, open joints or missing flashing is letting water in, putting in new brick without fixing the cause means the new brick will fail too. Look at the cap or crown, the joints and the roof junction first. Our guides on crown repair versus replacement and partial versus full chimney rebuilds show how these decisions fit together.

Things you can safely do yourself are limited to looking from the ground or with binoculars. Check for flaking faces, brick that has lost its outer skin, sand-like debris at the base of the stack, or sections of brick sitting loose. Stay off the roof.

• Take photos from the ground at the same spot each season so you can see change.
• Keep any fallen pieces to show a mason.
• Ask for the grade or absorption of any replacement brick in writing as part of the quote.

When to call a professional, and what this guide cannot tell you

Call for an inspection if you see brick faces peeling away, brick that crumbles under light pressure, leaning or bulging sections, or pieces of brick falling in the fireplace. Loose masonry is a safety question, not just a cosmetic one, so avoid standing or parking beneath the stack until it is checked.

This guide explains how brick is classified and why matching matters. It cannot tell you what grade or condition your brick is in. That takes a close look at the actual chimney, and sometimes lab testing for a sample. A chimney inspection is the way to learn whether your stack needs a few replacement units or more, and findings and options are explained before any work begins.

Frequently asked questions

Related reading

• Spalling brick and freeze damage
• Chimneys in older New Jersey homes
• Partial vs full chimney rebuild
• Chimney masonry repair and repointing
• Chimney repair