What Type Of Mortar For Chimney Crown

The basic mortar ingredients remain the same.

What type of mortar for chimney crown.

These types are type o type s type m and type n. The nps describes type n mortar as a mixture of 1 part cement 1 part lime and 5 to 6 parts sand. Mortar however is not the best material to make a chimney crown with because mortar crowns will often crack due to shrinkage enabling water to penetrate the chimney beneath. While the mortar rests prep the area by clearing away any loose debris.

As the chimney crown deteriorates it causes two things. If your plans include the replacement of a chimney crown and if you have never replaced. The most highly recommended material for properly built chimney crowns is portland based cement. A custom multi flue cap protects the concrete chimney crown as well as the flues.

Gap provided between flue lining and crown should be filled with compressible materials such as fiber glass etc. However if the draft is inadequate this should be addressed before considering a chimney cap. Mortar typically comes as a large bag of powder that must be mixed with water per manufacturers directions. For very severe weather applications consider a type s mortar mix made from 1 part cement 1 2 part lime and 4 to 4 1 2 parts sand.

Often masons will use leftover mortar to make the chimney crown. When applying the mortar to the crown form the mortar into an apex with the peak at the middle of the crown sloping down toward the edges. Think of it like a roof. First it allows moisture to run down into the masonry structure of the chimney causing spalling on the exterior bricks.

It acts as an expansion joint and also provides insulation for the flue lining. National parks service also recommends type n mortar for the majority of chimney applications. Used often but extremely poor in performance stone which outperforms all. The idea is to have the water drain away from the crown image 1.

The different types of mortar the first tip to remember when mixing chimney mortar is the four different types of mortar that are commonly used in building projects. Caps made from masonry mortar fail very quickly. After filling the gap between flue lining and chimney crown seal it using silicone or butyl caulk. A properly designed cap with a minimum 5 inch clearance from the top of flue should not interfere with chimney draft.

Crowns built out of thin mortar without proper reinforcement will eventually crack over time due to temperature changes and weather conditions. Mortar is used to provide a bed for the precast crown. A mortar cap or chimney crown that has been improperly constructed or one that has become deteriorated over time may be the cause of water leaking into your attic through cracks or broken mortar in the crown when this happens it is sometimes better to replace the crown than attempting to repair it.