Half-timbered buildings always have a certain proportion of stone materials: rubble stones for the foundations and cellars, bricks in the infills, paving stones of the courtyard, roof tiles, floor slabs, and ashlar stones at window and door jambs. Therefore, the stone restorers in the open-air museum have a lot to do. In addition to the construction work within the framework of new buildings coming into the museum, they are primarily responsible for the preservation of the infills and stone bases of the approximately 115 buildings.

The water mill at the museum entrance is being restored from the outside. Most of the work on the building is needed on the plaster surfaces. The mill has been standing in the museum grounds for 40 years and the weather has caused clearly visible damage.

During the restoration, the experts make sure to carry out the work according to the historical findings. The materials used are ideally the same as those used in the construction of the building. A lot of value is placed on authenticity. Frequently used historical building material is reused.

Since 1984, visitors to the museum have first encountered the Heller water mill from the Osnabrück district upon entering. Forty years have taken their toll on the half-timbered building. Weather influences such as wind, rain, and snow caused damage to the infill panels. Therefore, this year, the water mill will be fully restored from the outside for the first time.

The sides with the most damage are the weather sides: the west gable and the southern eaves side with the water wheel. For the restoration, these sides are scaffolded. The scaffolding must stand in the water for this.

The first task of the building restorers is to remove all loose and damaged plaster surfaces. It will probably be necessary to knock off the plaster down to the rubble stones or bricks. In the second step, the infill panels are re-plastered. For this, lime mortar is applied with a plastering trowel in at least two, possibly also three, work steps. The last layer of plaster must be flush with the adjacent half-timbered woods. The restorers smooth the last layer with the rubbing board and compact the surface. This restores the appearance as it was customary at the time of construction.

Once everything has dried, the painter can colour the plaster infill panels. The half-timbered framework, which was never painted, remains unpainted even now. With this, the restoration is completed