The product is indeed bonding and is perfectly acceptable as a backing coat internally. Under absolutely no circumstances whatsoever however should this material be applied to an external area....Never, never, never!!!!!
Bonding is however not strictly designed for use generally as a backing coat, it has many various uses but generally speaking what was used was browning and still is though for high suction backgrounds they now use hardwall. This was all before the advent of drylining which while in the uk is almost 100% the preffered practice is still not widely accepted in Ireland. The old fashioned methods of sand cement float and set (rendering and skimming are still the best) unfortunately there is a saturation of plasterers, so called, out there who dont know their a**e from their elbow!
Liteweight, anyone suggests using bonding to an external wall send em packing "tuite suite"