Refractory mortars are now easier to use, much safer and readily available. It is a specifically engineered mixture of sand, fireclay, calcium aluminate and cement. It is utilized to lay firebricks in places exposed to extremely high temperature. Refractory mortar is used to build fire places and is not applicable to hot faces.
Two types of refractory mortars are available:
Hydraulic setting mortar and
Premixed or Air-drying mortar
Hydraulic setting mortar is an apt choice due to its superior properties like acid resistance and water-insolubility.
Premixed or Air-drying mortar is used for indoor construction as it dissolves in water.
Jobs site mixed mortar is another type, which isn’t applicable now due to its inferior
Added to that, jobsite mixed mortar is another type, which is no longer applicable due to its inferior properties.
Types of Refractory Mortars
There are two types of refractory mortar that confirm to ASTM C 199 as permitted by code:
1. Hydraulic-setting Mortar
Its also referred as non-water-soluble refractory mortar and is also considered the best mortar.
Hydraulic-setting mortar is a mixture of aggregate and binder. It withstands temperature of 1499C for a minimum of 6 hours.
Outstanding properties of non-water-soluble refractory mortar are:
- Acid resistant
- Water insoluble
- It’s the only type of refractory mortar, which is suitable for setting clay flue liners.
- Hydraulic setting mortar is the same as Portland based mortar when it comes to workability and curing. Its also easier to ship and store than premixed.
- It also comes dry in bags and isn’t subject to separation, freezing or hardening before its used.
- It can be utilized to lay the firebrick, set clay flue liners and outdoor applications.
- It can be also used to set the throat and smoke chamber.
2. Premixed or Air-drying Mortar
Premixed refractory mortar is a mixture of clay, aggregates and a liquid silicate is used as a binder.
This type of mortar is inferior to hydraulic setting mortar. It dissolves in water after drying and requires long time to dry in wet environment. Added to that, premixed or air-dry mortar can result into efflorescence. It can be used in pails and can be thinned with little water.
Air drying mortar is preferable in hot and dry environment as it does not dry quickly as compared to other types of mortar.
It can be utilized in the construction of kilns and furnaces. It sets quickly after its laid and can also be cleaned easily since it dissolves in water.
3. Jobsite Mixed Mortar
Jobsite mixed mortar is widely preferred these days. It is formed by using sand, clay, fire, lime and Portland cement. It resists high temperature and when it cools down it losses the binder hence can no longer perform its function.
Thus jobsite mixed mortar isn’t suitable for locations exposed to high temperature regularly.
Practical Tips for Refractory Mortar
Maximum thickness of refractory mortar in high quality oven is 6mm.
Refractory mortar isn’t applicable for filling holes or gaps between firebricks.
Mortar thickness that is greater than 6mm, shrinks and leaves space between bricks and it eventually lets bricks move.
Refractory mortar should be used only for the brick structure to stay stable and strong. It should not be left exposed in the hot space.
Mortar thickness which is greater than 6mm isn’t allowed for locations away from the hot face.
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