Q: I have just had my brick chimney cleaned, and the chimney sweep said the crown — the top layer of mortar covering the top of the chimney — is cracked in several places and needs replacement.

The sweep took a photograph and I can see what looks like smoke stains around one of the cracks. I don’t have a cap, but would like to get one. My house was built in the 1970s, and I understand they didn’t always put them on back then.

I don’t see why we can’t just replace the mortar ourselves. But I’m concerned about the smoke. How did it get there if the flue is solid? Would the contractor do more than just fix the crown if there’s smoke leaking through it? The estimate to replace the crown is $425. Does that sound reasonable?

A: We suspect that over the years water infiltrated the mortar crown, causing it to deteriorate. But $425 sounds a bit pricey for simply replacing the crown.

If you’re comfortable on a ladder and walking around on the roof, by all means replace the crown yourself. It’s a pretty easy job, and with a little attention to detail you can do as good a job as any mason.

First remove the “rotten” mortar. It probably will just lift off. If it takes a little persuasion, a few gentle taps with a hammer and cold chisel will do the job. Be gentle. You don’t want to break any of the bricks or the flue liner.

Clean the newly exposed brick with a wire brush. Sponge the surface with water to remove the residue left by the brushing and to help ensure a good bond with the new mortar. Then apply the new mortar, molding it into a slope from just below the top of the flue liner to the first course of bricks so that water will run off.

For such a small job, we recommend you buy a sack of mortar mix, available at any home center, and enrich it with extra Type II Portland cement. The extra cement helps the mortar to stick to the bricks.

While you’re at it, inspect the mortar joints between the bricks. If the mortar is crumbly, now is the perfect time to re-point them.

Scrape the loose mortar away from the joints. We’ve found that a teardrop-shaped paint scraper is the right tool for the job. Dig about 1/2 inch of mortar from the joint and replace it with the same mix you used to build the crown. Spend $5 or $10 and invest in a pointing tool used by masons to tool the joints to match the rest of the chimney.

As far as the smoke stain, it’s impossible to know if it indicates a serious problem without inspecting it. We assume that you have a flue liner. If that’s cracked, that could be the cause of smoke stains. If it’s not, the stain is probably just a combination of dirt and soot.

But an ounce of prevention is worth a pound of cure. When you go up on the roof, take a flashlight, or better yet a drop light, and look at the inside of the chimney liner. It’s probably clay pipe mortared together in 2-foot sections. Look for cracked liner segments or deteriorated mortar joints inside the flue. If you see something suspicious, get the chimney professionally inspected. The chimney sweep should have done this, but it sure won’t hurt for you to double check.

If you’re interested in putting on a cap, you can do this yourself at the same time. You may need to remove the top course of brick from the chimney to install the cap. There are different types and styles of caps available. Check out the examples at: www.fireplacemall.com/Chimney_Caps/chimney_caps.html. Then measure the flue pipe, buy a cap and install it. You might also consult with a fireplace shop. The employees should be able to suggest the type of cap and guide you in installation.

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