The now exposed walls and floors of the Hawke's Bay Opera House have revealed once-hidden treasures that tell a story of the 100-year-old building.

A boxing bout card number, coming attraction signs, old fuses, a cigarette tin and wooden match box, and an odd light bulb on a stick contraption are among the finds.

More is expected to turn up while work continues, as part of the earthquake strengthening.

One of the other 'finds' the builders enjoy is discovering the many hidden spaces and old stairways from previous layouts that have changed over the years, said Gemco construction manager Eddie Holmes.

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"You can trace a buildings history as you remove walls; it is really interesting to see the decisions made over 100 years."

Hastings District Council's Opera House and arts precinct subcommittee chairman Malcolm Dixon said the discoveries helped tell the history of the century-old building.

"Looking at them, you can just imagine someone holding up the boxing card for the next round; someone hanging the coming attraction sign out the front of the building - or a chap out the back in charge of set changes having a sneaky cigarette. That must have been risky with things like sets and stage drapes around."

He said it was not uncommon for a "building of this age."

Council's facilities and programmes group manager Alison Banks said artefacts found during the work would be showcased within the finished building once the project was completed.

About 400 cubic metres of concrete is expected to be poured into the Opera House within the next six months - using 150 concrete trucks.

The $11.1 million earthquake strengthening of the Opera House started on August 2 and is expected to take 20 to 24 months.