Auckland's iconic Heritage Hotel is quite literally crumbling - but it's all cosmetic.

Chunks of plaster and masonry were noticed coming away from the former Farmers Department Store in September last year.

The building's facade was erected in 1934, stuck to the original 1921 building using metal ties.

They're now rusting, as water has got in between the facade and the original building.

Gary Jarvis of Heritage Hotels says engineers are looking into the issue, but he's sure it isn't structural.