Err, reality check here. The chap wants to build a BBQ. Strength is
not important. Portland cement with careful attention to ratios is
what you use when building multi-storey carparks, motorway bridges and
runways for Jumbo jets. Not for BBQs. Lime is kinder to the planet
than cement. Come to think of it, we'd be better off without
multi-storey carparks, motorway bridges and runways for Jumbo jets so
lets just drop this whole cement addiction thing.
In fact, for a BBQ, I wouldn't even bother about the lime. Bond the
bricks with a sand / clay mix roughly 3 to 1. For the clay you could
dig it up from your garden. Remove the topsoil and use whatever is a
foot down. (You'll be half way to a water feature at the same time)
Most non-timber houses in the world are earth bonded with no cement.
Earthquakes can be a nuisance but shouldn't trouble an English BBQ
overmuch. Relax and enjoy the summer without stressing on mortar.