Repointing a Kirkland chimney means matching what is actually there

Genuinely old masonry is rare here. Of roughly 41,910 Kirkland housing units, about 252 date from 1940 to 1949 and about 253 from 1939 or earlier — a little over five hundred houses in the whole city. Against that, 10,541 units went up in the 1970s alone.

That changes the conversation about mortar. The governing rule does not move: a repointing mix has to be no stronger in compression than the mortar it replaces, and the selection principle is to take the weakest mortar that still does the job, because a mix harder than its surroundings pushes movement stress into the brick faces and spalls them. What moves is the starting point — matching a mid-1970s portland-based mortar is a different exercise from matching a soft historic lime one, and putting a historic mix on a modern stack is as much a mismatch as the reverse.

It also changes what failing joints mean. Mortar of that era does not usually erode simply because five decades have passed, so on a chimney of Kirkland's common vintage the first question is what has been keeping the joints wet.

Spalling is the brick's outer face flaking, popping or crumbling away, and it comes from water inside the unit rather than weather on the outside of it. Brick that takes on too much water can spall, crack, craze or disintegrate as it cycles through freezing and thawing.

So the first thing worth doing is walking around the chimney. Wet-season wind here blows from the south or southwest, so one elevation takes driven rain while the others largely do not — and the Brick Industry Association's position is unambiguous: heavy wind-driven rain penetrates a single wythe of brickwork whatever the quality of the materials or the workmanship. Saturation runs highest on the loaded face, and that is usually where the story starts.

• Mortar you can rake out with a house key. The binder has gone. This is the clearest case for repointing, and joints receded more than about a quarter inch are already past the industry's maintenance trigger.
• Thin brick flakes in the gutter or on the ground. Spalling in progress. The face is the wearing surface, and once it is off the brick behind it absorbs faster.
• A white bloom that keeps returning after cleaning. Efflorescence that comes back is the Brick Industry Association's signal of a water path still open, and it says find the source before attempting repairs.

This is the practical question a Kirkland homeowner rarely gets answered. The National Park Service puts the working range for repointing at wall temperatures of roughly 40 to 95 degrees Fahrenheit, so that a fresh mix neither freezes nor gives up its water before curing, and the mortar goes back in thin lifts that each have to reach thumbprint hardness before the next.

Set that against the year here. Roughly three quarters of the region's precipitation falls between October and March, and December and January frequently record rain on 20 to 25 days or more each month. That does not make winter repointing impossible; it makes it work that needs protection and a real dry window rather than a date.

• If the joints are failing but the top is sound. The repointing can wait for a workable window. Nothing is gained by rushing mortar into a saturated wall.
• If a crown, cap or flashing is feeding the joints. That comes first regardless of season, because repointing over an open water source means paying for the mortar twice.

A replacement brick has to match what is already there in physical behavior as much as in appearance — absorption and strength, not only color and size — and any unit going where it will be wet and freezing has to be severe weathering grade, proven by fifty freeze-thaw cycles or by limits on strength, absorption and saturation coefficient.

Repointing renews the sacrificial part of the wall. It does not correct movement, and it does not rescue brickwork that has lost too much of its face.

• Cracks through several bricks, stepped or diagonal cracking, or a stack out of plumb. Movement rather than weathering. This is investigated, possibly by a structural engineer, before mortar work is specified.
• Widespread spalled brick rather than isolated units. Individual badly spalled bricks are cut out and replaced. Once it is general across an elevation, replacement stops being the economical answer.
• A quarter to a half of an area already needing work. Spot repointing is preferred where it holds, but past roughly that share, doing the whole elevation in one access setup is usually the more sensible call.