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Frequently Asked Questions
Is refractory cement a Portland cement?
No, it is a different material.
Usually a calcium aluminate cement.
Different raw materials and process.
It sets through different chemistry.
That explains its unusual behaviour.
What is it used for?
Laying and jointing fire brick.
Casting refractory shapes.
Linings for kilns and furnaces.
Forges and wood-fired ovens.
Anywhere sustained high temperature occurs.
Why not use ordinary mortar there?
Portland cement degrades at those temperatures.
The paste breaks down rather than weakening.
Joints then fail before the bricks.
The assembly comes apart at the joints.
It is not a marginal difference.
How fast does it set?
Very fast, reaching in hours what Portland takes days.
That suits repairs and quick returns to service.
Working time is correspondingly short.
Batches must be kept small.
Mix only what can be placed.
Can it be used structurally?
It is a poor choice for ordinary structures.
Its strength can reduce over time.
Warm damp conditions cause that change.
The hydrate structure converts.
Early strength is misleading here.
Can it be mixed with Portland cement?
No, and this matters on site.
The combination can flash-set.
It goes off almost immediately.
Keep tools, buckets and boards separate.
Never gauge one with the other.
Is a ready-mixed version available?
Yes, and it is usually more practical.
Refractory mortars come formulated.
Castables include graded aggregate.
Both are matched to a temperature range.
Buy for the service temperature required.