To be fair, they are the experts and they should know what they are doing and telling you what mix should be being used.
Their mix may be approved by architects, but that means nothing as there are many different specs of buildings.
They are wrong they can't call a cement lime mortar, lime mortar, they must call it cement lime.
Hydraulic lime mortar is very different and requires the correct type of sand, it's also more expensive.
There is plenty of evidence online as to why hydraulic lime should be used.
Try and find a surveyor who specialises in old buildings
Their mix may be approved by architects, but that means nothing as there are many different specs of buildings.
They are wrong they can't call a cement lime mortar, lime mortar, they must call it cement lime.
Hydraulic lime mortar is very different and requires the correct type of sand, it's also more expensive.
There is plenty of evidence online as to why hydraulic lime should be used.
Try and find a surveyor who specialises in old buildings