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Chimney Work, Part 1

by on July 25, 2014

So, I was up on the roof tearing off leaky shingles, and found some thin pieces of concrete in my work area. Looking around, I walked up to the chimney, and found this.

Flaking Chimney Cap

Crack spanning brick, concrete, and clay flue liner

Needless to say, this was yet another thing I needed to fix. Doing some research online, I discovered that the optimists say this sort of chimney top lasts 15 years. (And the pessimists say you need to inspect it every spring, and be prepared to slap on another layer if it’s cracked over the winter.) There’s another style, that the optimists say lasts a century or longer, if done well. Since my guiding philosophy for this is to make repairs so that they’ll outlast me, the replacement will be in this second style. (I also learned that the terminology is thoroughly confused: Some use “cap” to refer to this concrete topper, and “crown” to refer to the little metal thing on top that mostly keeps rain from going down the chimney. And some reverse those meanings. And some interchange them randomly.)

So, I took a couple of days off in mid-week, thinking that the first day I’d tear off the old, flaking concrete; patch a few cracks in the mortar (and that big crack that broke one sandstone “brick” into two); and build the form to pour concrete in for the new top. And the second day, we’d borrow a cement mixer, mix up cement to pour in, and haul it to the roof in batches.

The tear-off went decently well. Standing a little “uphill” on the roof, the chimney looked like this, just before I began tearing it off.

Most of the concrete above the brick level came off with just fingertip pressure on cracks and such. For the rest that I tore off, I used a mason’s hammer, mostly the pick on the back.

Based on my readings of several “how to” sets of instructions, I had expected the chimney to be mostly hollow from basically the top of the bricks up. Instead, the concrete turns out to fill the chimney, at least to the depth of the top brick.

Chimney top flat

Although it’s not entirely clear in this picture, the top is still a little convex, especially on the right. I wound up taking it a little bit lower (and then failed to get a new picture), but it’s pretty much at that level. By the time I was done with that, some of the cracks I’d known about had become much worse. This is the scariest-looking corner.

Cracks in mortar and missing mortar

Then I got to work. Other than a gallon jug of water, these are the tools and materials I used:

Tools and materials

Because the cracks were most likely the result of water running into the mortar and freezing there, I chose a cement that is more resistant to water penetration than most. I used the measuring cup to measure both the water and cement. It would be a little more convenient if I’d measured the water and cement in different containers, as some cement inevitably started hardening in the measuring cup between batches. The quart container on the left I used to mix the cement in, and the pointing tool in the foreground I used both to apply and smooth the cement. You also want to be wearing gloves of rubber or plastic; cement is caustic until it’s cured. I used a cheap pair in Home Depot orange, that has some sort of rubbery-plasticy stuff on the grip side and allows sweat to escape on the back. 

This cement begins to harden 2-3 minutes after it’s mixed, so I didn’t take any action shots of the mixing and spreading. But here’s what that corner looked like after I’d filled the cracks.

Cracks filled

Also, there’s a funny thing about the chimney: When you’re sitting on the roof looking up at it, you see a *lot* more cracks, than when you’re standing on the roof looking down. How many more? Put it this way: In two days of work, I patched the cracks on two of the chimney’s four sides.

So, it’s Friday night, and I’ve a weekend with no responsibilities to fulfill. You’d think I’d have it all done by sundown Sunday, right? Well, probably not. You see, there’s a lot of rain forecast for the weekend. And rain makes roofs slippery. It sometimes washes away cement that’s not set sufficiently. And rain falling into a tub of cement powder, turns your chimney repair materials into a small anchor, suitable to hold your kayak or small canoe in place while you do something else. So, if I get up there at all this weekend, it will be some time that it’s not been raining for long enough that the roof and chimney are dry, and it’s not expected to rain for a few hours.

I’ll fill the cracks on all four sides before I proceed to the next step; before I’m finished, I’ll be putting something like 600 or 700 pounds of concrete on top, and I want to be as sure as it’s possible to be that the chimney will hold it without problems.


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