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How to Repair A Damaged Chimney Crown

The chimney crown is the portion of the chimney that is between the opening of the stack and the cap that rests at the topmost pinnacle.

The crown surrounds the chimney and is designed to slough away water that the cap blocked from entering the flue. It has sloped edges to direct the runoff and overhangs the rest of the stack, providing shelter for the more vulnerable brick and mortar.

Fixing a damaged crown can either be one of the easiest possible repairs to make to your chimney, or one of the hardest. How involved the task is depends on the extent of the damage.

This article will give you an overview of the importance of maintaining your chimney crown, how to identify the extent of the damage, and how to make the necessary repairs.

Risks of A Damaged Chimney Crown

Damage to the crown of the chimney presents a threat to the integrity of the rest of the structure, and potentially to your home.

The crown is not just a decorative topper, it serves a vital protective function. If your chimney crown is damaged, it will allow water to leak into your chimney.

The primary purpose of the crown is to prevent water from rain and snow from affecting your chimney.

The sloped sides direct water to run away from the opening of the flue, and the overhanging edge of the crown provides shelter for the brick and mortar of the smoke stack, elongating its lifespan. Water can cause damage in different ways, depending on where the crown fails.

If the crown fails to prevent water from running down the outside of the stack, it can cause freeze-thaw damage, exacerbate cracks, and erode the mortar binding the bricks. This can eventually cause the stack to collapse. If the crown fails to stop mortar from seeping within the bricks, then the mortar can be degraded from within.

The bricks are also able to absorb a significant amount of water, approximately 1 ½ cups per brick. The water can dissolve the mortar, soften the bricks, and increase the weight of the stack. If the crown fails to prevent water from running into the flue, then the interior of the chimney can suffer damage, as can your fireplace, hearth, and damper.

This can prevent smoke or carbon monoxide from being properly vented, allow sparks into the wood structure of your house, rusts the damper shut which prevents the release of smoke, compromise the heating efficiency, and allows outside elements directly into your home.

How to Repair the Chimney Crown

If the crown of your chimney has still maintained its original shape and there aren’t any large chunks missing or edges that have eroded away, then you don’t have to replace the entire thing.

You can easily seal up cracks with only a few simple tools and a few minutes. Regularly reapplying sealant is also a good preventative measure to avoid greater damage over time.

  • The Materials You Will Need
    • A Trowel
    • Mortar, Caulk, or Silicone Sealant
    • Crown Sealant
    • A Broad Paintbrush
    • A Steel Chisel
    • A Ball peen hammer
    • A Wire Brush
  • How to Reseal the Crown
    • Use the wire brush to clean the crown of dust and debris. Take this opportunity to test how badly damaged the crown is. Make sure you aren’t able to pull off any big chips or see exposed brick. If you can, you will need to replace the crown. If you can’t, then you can just reseal the crown. 
    • Use a trowel and caulk or silicone sealant to fill in the largest cracks. Be especially careful to seal up ALL cracks that have any separation. Cracks with gaps are in worse shape and need more care.
    • Apply a liberal amount of crown sealant to the crown and use the paintbrush to smoothly distribute it. Build up a thick layer that has edges sloping away from the flue. Make sure to thoroughly seal the points at which the crown connects to the flue to prevent any water from seeping in.
    • Finish the crown off by adding or replacing the chimney cap. The cap is screwed into the flue over the crown itself. Make sure that the cap is also large enough to overhang the crown so that runoff water stays away from the flue opening.

How to Replace or Rebuild the Chimney Crown

If there are chunks taken out of the crown, if the edges have eroded away and exposed the brick underneath, or if the crown has lost its shape, in particular its slopes, then it will need to be completely removed and replaced.

Replacing a chimney crown is far more time consuming and work intensive than a simple repair, but it is still possible to do on your own.

  • The Materials You Will Need
    • A Trowel
    • Mortar
    • Silicone Sealant
    • Crown Sealant
    • A Chisel
    • A Ball peen hammer
    • A Wire brush
    • Concrete Mix
    • Wood framing
  • How to Rebuild the Crown
    • Using a chisel and ball peen hammer, chip off all of the concrete comprising the damaged crown to completely remove it. Make sure to chip the concrete off of the brick and mortar stack, the flue, and anything else it is bonded to to get as clean a surface as possible.
    • Use the wire brush to finish removing leftover concrete and clean the bricks of dust.
    • Make a frame for the crown out of wood. The frame pieces should have at least a 15 degree bevel to facilitate the construction of a slanted crown.
    • Construct a grid structure base out of steel. Alternatively, you can lay down a piece of sheet metal or a concrete sheet. This creates a bond break, which will reinforce the crown, keep the shape, and prevent concrete from running into the flue when poured. The bond break also, as the name suggests, stops the concrete from bonding with the surrounding masonry to accommodate for the difference in the rate of expansion and contraction due to weather.
    • Put the frame in place and go mix your concrete.
    • Between the flue and where the crown will meet it, put ¼ inch of silicone sealant and compression material. A good choice for the compression material is ceramic wool. This will allow for the different materials between the crown and stack to expand and contract at different rates without separating.
    • Pour the concrete in the frame and let it set for at least 24 hours.
      • To prevent the concrete from sticking to the wooden frame, use a thin piece of oiled cardboard as a barrier between the two.
      • When pouring the concrete, make sure to leave at least two inches of the flue sticking up from the crown, rather than pouring right up to the edge. Different cities have different recommendations and laws, so check your area.
    • With the concrete set, brush sealant onto the crown until it is completely covered and smooth. Make sure to preserve the sloped edges. Pay special attention to make sure the points between the crown and flue are thoroughly sealed.
    • Add or replace the chimney cap. Since you should have left at least 2 inches of flue length, you should have enough room to screw it directly into the flue. Double check that the cap is large enough to fully cover the flue opening and properly overhang the crown. The crown should not allow any water directed by the cap to get closer to the opening of the flue. If it can, your cap may be too small, or the slopes of the crown may be too shallow. In either case, you will need to fix the issue.

When to Call a Professional

Although resealing a crown is easy to do on your own, rebuilding the crown is much more difficult. It involves more tools, greater expertise, more time and planning, and provides far more opportunities to make costly mistakes. If you aren’t confident in the efficacy of your masonry skills, you may want to simply hire a contractor to come help you.

In addition, you need to be comfortable with heights and working on tall ladders. If you are not accustomed to this type of work, you may be better off hiring a professional.

Falls can result in thousands of dollars in medical bills, lost time from work and other life activities, and pain and suffering. You should never work on a tall ladder alone. Someone should always be present to hold the ladder while you climb, and a safety harness is always recommended when working on a roof.

Crown repairs are fairly inexpensive chimney repairs, typically running below $1,000 even for rebuilding. Considering the damage caused by a faulty chimney crown can easily exceed ten times that price, calling a qualified chimney repair service for your crown will never be a bad idea.

If you do wish to use a contractor or repair service, make sure that they are qualified to do crown repairs. Inexperienced repair persons will sometimes try to cut corners and rebuild your crown entirely out of mortar.

Mortar cannot withstand the elements, and will fall apart quickly. Your crown must be made from concrete or another weather resistant material and it must be properly sealed in order to work.

All in all, chimney crown repairs should take less than a day, not counting the time it takes the concrete to set.

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