Q: After a hard rain, we found water in our basement near where our chimney attaches to the house. We noticed that the caulking between the chimney and the house is dry and cracking. We also noticed that the basement’s ceiling has water spots, which leads us to believe it has happened before.
Is there a special caulk we can use after we remove the old material? And some of the mortar between the bricks is cracked. Our house is about 30 years old.
A: A 30-year-old chimney needs a good inspection. You can do the inspection on the outside yourself. But we recommend that you get a chimney sweep for the inside.
Over time, creosote, a byproduct of wood, builds up in the chimney liner. Creosote buildup is the main cause of chimney fires. If you use the fireplace regularly during the winter, an annual inspection and cleaning is a must.
As for the chimney’s exterior, get on a ladder and take a look. Pay special attention to the joints, where the chimney meets the siding. Cracked caulking means water penetration for sure, but also pay attention to where the roof meets the chimney.
Is the flashing in good shape? If not, this could be a cause of leakage, too. Recaulking is in order, but first take a look at the mortar.
Given that you have cracked mortar joints, we suspect that the mortar is beginning to fail. Test the joints by trying to remove some mortar with a teardrop paint scraper. If mortar comes out in a granular mass, it’s time to repoint the chimney, which means replacing the decayed mortar with new mortar.
First, scrape about an inch of mortar from the joints. You can either do all the scraping at once or you can scrape as you go. While you’re at it, scrape out the old cracked caulk where the chimney and the siding meet.
To replace the mortar, you’ll need a pointing tool and some mortar. A point tool is a handheld metal tool about a foot long with two half-round sides on the ends. Mix the mortar to the consistency of thick peanut butter. If you use packaged mortar mix, we suggest you enrich it with some additional Portland cement.
Brush the joint with a wet brush. The added moisture will seep into the existing mortar and allow the cement to seep in. This will provide a stronger bond between the old and new work. Pick up some mortar in one hand and coax it into the joint using the pointing tool. The first few times you’ll lose a good bit of mortar. Don’t worry, pick it up and use it on the next joint.
Let the mortar dry for 20 minutes or so. Then tool the joints with the pointing tool. The tooling produces a smooth finished joint. Let the mortar dry for a few days before caulking the joint between the siding and the chimney.
Caulking brick should be done with paintable clear caulk. Paintable clear caulk goes on white but dries clear after a few hours. Unless you’re perfect, white caulk can make a mess on brick. If clear caulk is not available, choose an elastomeric caulk. Use blue painter’s masking tape on both sides of the joint to get a crisp, clean line.
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