Damp weather and well-intentioned attempts at restoration are combining to put at risk important wall paintings in castles, abbeys and churches across England.

English Heritage on Tuesday sounded an alarm call for the 77 wall paintings it cares for, from 12th-century visions of eternal damnation at St Mary’s church in the Forest of Dean to the adoration of the magi at Berry Pomeroy Castle in Devon.

Rachel Turnbull, the senior collections conservator at English Heritage, said wall paintings were the most challenging type of art to care for, but they offered “a precious insight” into the nation’s history.

Facebook Twitter Pinterest A mural at Longthorpe Tower in Peterborough. Photograph: Richard Lea-Hair/English Heritage

“For thousands of years people of the past have left little traces, glimpses into their everyday lives through richly decorated wall paintings,” she said. Whether domestic or religious, “these artworks tell a story about the people who painted them and the communities who lived or worshipped in these buildings centuries ago”.

“If they are to survive for future generations to enjoy, we need the public’s help today to repair their buildings, stabilise their structures and protect them from damp and decay before time runs out.”

English Heritage is appealing for donations and says just £20 can pay for specialist mortar to be mixed and used to repair plaster damage, while £75 can pay for multispectral imaging revealing things invisible to the naked eye.

It gave three main reasons for the risk, one of which was the weather. It said: “Unlike the well-preserved paintings in France and Italy’s warmer climates, England’s wall paintings are being increasingly affected by damp and wetter weather, which is causing damage to their fragile structure.”

Facebook Twitter Pinterest St Mary’s church, Kempley. Photograph: Richard Lea-Hair/English Heritage

Also to blame are early 20th-century attempts at restoration doing more harm than good, and the fact that the paintings cannot be removed and are often on the walls of ancient buildings, themselves at risk.

England’s wall paintings date back as far as 100 AD, with images of nymphs on a wall of Lullingstone Roman Villa in Kent. Nineteenth-century examples can be found at St Mary’s church at Studley Royal in North Yorkshire, one of the finest examples of high Victorian gothic revival architecture in England with its extravagantly decorated interior.