It could take 10 years to clear a backlog in documenting the full collection of art treasures and artefacts at the National Museum and Galleries of Wales, says a new report.
The Museum says £3.5m from the Assembly Government will help improve storage
The Auditor General for Wales found basic computer records exist for about a third of its collection.
It could also take 20 staff 20 years to clear the backlog in storing items.
The museum said it had increased information held on computer by 200% in recent years but if it concentrated wholly on this area, services to the public could suffer.
The backlog includes recording items ranging from paintings to locomotives, and from shells to ancient coins.
The Auditor General for Wales Sir John Bourn congratulated the museum on improvements since his last report but said more were needed.
However, the museum estimates it would take 384 staff years to clear.
At current funding levels, the estimate is that the museum needs another £1.65 million over 10 years to deal completely with the outstanding items.
Although over the last few years, storage space has improved, the report says more needs to be done in this area.
The Assembly Government has now earmarked £3.5 million for this work to continue
But it would take 20 dedicated staff 20 years to deal with these backlogs.
Items that are not stored appropriately are at risk of deterioration and there have been examples of damage such as to boats at the Museum of Welsh Life.
Tackling the backlog can't happen overnight says the Museum
Sir John said it was "essential" that the museum prioritises its resources to ensure it drives its programme of improvements even further forward.
He added: "The backlogs that persist mean that much of the collection is not maintained as well as it ought to be and that this needs to be addressed to preserve Welsh National Heritage for future generations.
"Until these are dealt with, the public cannot take the full advantage of all that the museum has to offer."
Robin Gwyn, of the museum said conservation was not something which could be undertaken quickly.
He said: "It's a time consuming area of work. To have to assess the size of an object, its location, its ownership, its condition, all those details have to be gathered in a painstaking way, you can't cut corners, it does mean extra people."
One of the museum's painting conservationists Eleri Evans added: "You have to make sure work is kept in a stable condition, you care for it, you clean it and investigate it and sometimes unexpected things can happen."
Mr Gwyn said there were backlogs in every museum but the right balance between such curation work and the visitor experience was a delicate task.
"Were we to concentrate wholly on ensuring that all records are computerised over a short period, then other aspects of work, such as services to the public might have to be revised to enable this work to be completed."
Museum officials will be answering questions from the Assembly's audit committee next month.