York Castle Museum opened as normal today but offering discounted tickets due to its partial closure.
Owners York Museums Trust revealed last night that they had found Raac, the collapse-risk concrete, in parts of the building.
Today it was displaying notices about the partial closure outside the entrance to let visitors know.
The north side of the building, which houses Kirkgate, the Period Rooms and Shaping the Body has Raac (reinforced autoclaved aerated concrete) in the roofing.
It is shut as a precautionary measure.
The rest of the museum, including the Prison Cells, the Sixties Gallery and the First World War Gallery will remain open.
Prices have been more than halved during the disruption – for adults it is normally £14.50 online/ £16 walk up price, and £8.75 online/ £9.75 walk up for children.
A spokesperson for York Museums Trust told YorkMix: “We are introducing reduced prices to the museum from today – £7 for an adult, £4 for a child and £6.30 for a student.
“We also have a range of other concessions, including all children age 0-16 who are York residents are able to visit for free (on proof of address). The tickets are annual and enable a return visit for a year.
“We will be offering refunds or discounts to those who have pre-booked tickets for a visit over the next couple of weeks. We are currently putting the measures in place which will enable us to do this.
“A specialist inspection will be taking place in the near future.”