Standard mortar

[theboss]

When building a brick arch doorway is it ok to use a standard mortar mix? By that I mean sand 4:1cement. I was chatting to a brickie mate and he said the mortar is likely to crack due to the large heat variance.
Last thing I want it the arch collapsing, so would you add a fire proof additive, or use home brew for the arch?

[oblertone]

Use homebrew, the cement will burn out but the lime component will keep it together.

[truckcab79]

Personally if he knows what he’s doing I ask him what he advises instead. I used a standard mix and I do have one hairline crack, but an arch is self-supporting so it can’t really go anywhere. That said mine, and I think most are also tied back into the structure behind it (using galvanised wire inserted into the arch joints and mortared back into the dome behind.