The Ontario Building Code | Mortar for Chimney Liners
9.21.3.9. mortar for Chimney liners
(1) Chimney liners used in chimneysfor solid fuel-burning appliances shall be laid in a full bed of,
(a) high temperature cement mortar conforming to CAN/cgsb-10.3, "Air Setting Refractory mortar", or
(b) mortar consisting of one part Portland cement to three parts sand by volume.
(2) Chimney liners used in chimneysfor oil- or gas-burning appliances shall be laid in a full bed of mortar consisting of one part Portland cement to three parts sand by volume.
In Plain Language
This clause sets the mortar spec for chimney liners depending on fuel type: high-temperature refractory mortar or a 1:3 Portland cement-to-sand mix for solid-fuel liners, and the same 1:3 mix for oil- or gas-burning liner joints.
Common Questions
Q: Can I use regular mortar for a wood stove chimney liner?
Only if it's high-temperature refractory mortar meeting CAN/CGSB-10.3, or a 1-part-cement-to-3-parts-sand mix. Standard bricklaying mortar without these specs doesn't meet this clause.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.