The Crown (sometimes inappropriately referred to as the cap) is a concrete slab that should be poured at the top on all chimneys. When pouring a new crown, the old mortar wash/crown needs to be completely removed and a new crown should be formed and poured so that it over-hangs all brick/stone on all sides of the chimney. Many chimneys in our area were built with just a “mortar wash” to save time and money during construction. The masons would take the left over mortar and smear it over the top of the chimney.
While this would last until the one year construction warranty was up, they will eventually crack and start to allow water to penetrate into the chimney. The end result is major deterioration to brick/stone chimneys, as well as water leaks inside the home. THE MOST IMPORTANT PART OF YOUR CHIMNEY IS A PROPERLY CONSTRUCTED OVER-HANGING CONCRETE CROWN.
A Chimney Crown is located at the very top of your masonry chimney chase. It protects the interior chase system from moisture, as well as the masonry structure below. The chimney crown is designed to have a gradual slope from the flue’s venting through the chimney, allowing water to roll away from the chimney flue systems. The overhang then prevents water from rolling down the face of the chimney structure, providing another level of protection for your masonry chimney from the elements. When constructed, care is taken to create a seal around the chimney flues to allow for expansion and contraction with changing temperatures both within the chimney flue and exterior weather conditions.
If you do not notice that the concrete crown overhangs your masonry chimney, you may have what is known as a Splay or Mortar Wash. Both practices are often seen in home construction, however in our experience require a higher level of routine maintenance and a higher risk of failing and causing a leak into the home.
A flexible waterproof sealant called CrownCoat may be recommended if your concrete crown has minor cracking or defects, to prolong the life of your crown and prevent water intrusion.
Water is one of the most detrimental elements your chimney faces. Causing over a billion dollars in repair costs annually, it is important to protect and prevent damage to your masonry chimney. Moisture absorbed into the brick or stone can cause spalling, discoloration from efflorescence, and insulation and structural failure. When we repair or come into contact with a masonry chimney, we will recommend the masonry chimney to be waterproofed with a 100% vapor permeable, water-based, and environmentally friendly waterproofing agent. We use a water repellent vs. a sealant, as we want the brick or stone to be able to maintain it’s vapor permeability, allowing moisture to leave the masonry while preventing absorption at the exterior. The product goes on clear, does not induce a sheen on the masonry, however when exposed to rain allows the water to bead off of the chimney.