The interior decorative wall paintings as they appear in the house today probably date from the late 18th or early 19th century.

In 1979 two museology students from the University of Stellenbosch carrying out some practical work, set off a chain of discoveries which finally revealed that the so called authentic 18th century murals on the walls of most of the rooms were incorrectly repainted in the 19th and 20th centuries. Dr Purcell who had led the first major renovations of the house had already indicated in his personal notes that many more rooms had been decorated with murals but that owing to the lack of funds only a portion of the rooms could be restored. The only authentic visible murals were those in the dining room, entrance hall and lower hall which were revealed by Dr Purcell underneath layers of wallpaper.

Subsequent to the discoveries of the original 18th century murals it was decided not to strip the walls and retouch the authentic designs as more than 50% of the originals had been destroyed over the years as a result of alterations, replastering and dampness. Instead it was decided to reconstruct the designs on the basis of the results of more test strips and using Dr Purcell's records. This project took more than a year to complete.

The styles of the murals vary from room to room and could have been influenced by the fashions of the time. The styles range from Neoclassicism in the lower hall reflecting the classical architecture of the front of the house to the elaborate decoration with its interesting medallion above the fireplace in the music room, and from soft pastel colours in the drawing room to the arabesques in the dining room.

It is interesting to see how the artist created a three-dimensional illusion by adding shadows in the designs. The murals in general demonstrate a high standard of craftsmanship. There is no conclusive evidence on who painted the murals or how many artists worked on them. Traces of similar paintings have been found in other buildings of the same period such as Uitkijk, Boschendal, Grosvenor House in Stellenbosch, as well as Rust-en-Vreugd and the Sendinggestig Museum in Cape Town.

The murals at the Koopmans-De Wet House are unique in their variety and use of skilful techniques. They are, however, presently in urgent need of attention as a result of damp problems and of wear and tear.