Brick Repair
These mortar joints are unusually thin to start out with but must be tuckpointed back in and the column waterproofed.

A fireplace provides so much warmth to your home, not only in heat but adding a certain level of charm to the room it resides in. A hearth can be decorated for the holidays and be a real focal point of room if you wish. The cold reality of a chimney, however, is that you will more than likely need to do some type of maintenance work on the chimney during your time living in any home. Chimneys extend above the roof line and therefore get no protection from the rest of the home from the elements. Bricks often crack from water damage, but arguably the most common repair needed on a chimney is mortar replacement. In chimney sweep terms, this is a tuckpointing repair.

Missing mortar joints in between bricks are extremely common on brick chimneys. The mortar often erodes away from water damage or cracks and crumbles out through damage incurred when water freezes and thaws. Tuckpointing these joints back in is generally not difficult. Sometimes, very extensive damage requires more extensive repairs which may include rebuilding part or all of the chimney, but for minor damages tuckpointing is an acceptable repair.

To tuckpoint your mortar joints back in, you must first remove any existing damaged mortar. Often times little bits will cling to the brick. Using a mason’s chisel, a hammer, and a scraper, gently remove any clinging mortar from between the brick. Be careful to not damage the brick. Packaged mortar that you just mix water with is usually pretty good. Every mason will tell you the ingredients that they think are best for mortar. The most important part is to make sure that the mortar joints are completely packed. The easiest way to ensure this is to put mortar on a board and hold it up right below the mortar joint in question. Using a trowel pack the mortar into

Brick Repair
These mortar joints are crumbling and should be chiseled out and tuckpointed back in.

the joint completely. Strike off extra mortar by using a trowel and holding it flat against the brick to slice off the mortar that is extra. Using a jointing tool, press the mortar in so that it is neat and compressed and does not look sloppy.

Water proofing your chimney is always recommended after any repair. Since the brick had to be repaired in the first place, it is obviously susceptible to further damage of the same areas or new damage entirely. Water is a huge cause of damage to any masonry structure. It is important to select a water repellent that is not film forming because a film forming water repellent actually does more harm than good. Although a film that is not permeable is desirable in that it does not permit water to pass through to touch the brick, it also traps water vapors under the film which wreak havoc on the brick beneath the film causing it to spall and crack. A water repellent that forms a semi-permeable membrane over the brick which does not allow water molecules to pass through but permits water vapors naturally found in the brick to exit is preferred.

Clay Lamb

Clay Lamb is a Cincinnati Chimney Sweep contractor and the executive producer of the YouTube channel, podcast, and blog Ask the Chimney Sweep. He is also an award-winning educator and public speaker in the chimney and fireplace industry.

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Clay Lamb

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2 thoughts on “Crumbling Mortar on Your Chimney

  1. Hi Clay. We recently purchased a 100-year-old home with 8 fireplaces, which we do not use and have no intention of using–BUT we are concerned about deterioration. All of them need new fireboxes and refacing, but what concerns us most is that that all fireboxes have to be regularly vacuumed due to what I assume are small falling bits of crumbling mortar and dust. Does this mean that the entire inside of the chimney, from top down to firebox, needs to be repointed or relined? If so, which would you recommend? If not, do you have any idea of what might be happening here? We know nothing about any of this and I’m having a difficult time finding information on the internet.

    Many thanks for your time.

  2. Number one, you’re more than welcome to call my office, it sounds like probably a 15 minute or 20-minute call. 5136624600. As a sidebar note, you can put a plate over the top of the chimney to help stop wind and water to help with the deterioration of the mortar that is separating from the sand mixture into the firebox. additionally, you can install bags of insulation from the battings, this will help some, but the sand will still accumulate above the insulation material. the sand will still be a nuisance as you’re describing. I would attack these eight chimneys one at a time. I have told many people to consider how to use them as candle racks as I’ve told my friend in my beautiful historic Covington Ky, you can use an odd number of different size candles put a screen in front of it, some fireplace tools and enjoy a beautiful romantic night. Just don’t stuff it with combustibles or newspaper!!

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