The Winter Garden Today

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2.1 Maintenance of the structure

When king Leopold II passed away in 1909, the ownership of the Royal Glasshouses passed on to various institutions. The land, purchased by Leopold II, and the glasshouses constructed on that land, became property of the Royal Donation, a semi-private institute. The other glasshouses, situated on the piece of land that he received to fulfil his duties as a king, are owned by the Regie der Gebouwen, a governmental institution. The borderline between these two adjacent properties can be diagonally traced through the Congo House (Figure 1, no. 4). The shared ownership of the glasshouses does not facilitate restoration procedures.

Since the death of Leopold II, few of the Royal Glasshouses were restored. The Winter Garden merely received some refurbishments in the 1980's, funded by the Regie der Gebouwen.

Some cross-sections were reinforced by welding new parts on to the old ones. However, the weldability of the initial material was never investigated and therefore the durable efficacy of this intervention remains questionable. Heavily corroded profiles were replaced, yet without recording these changes in an appropriate report. The whole structure was sand-blasted and

Figure 4. The structural parts of the Winter Garden (Vierendeel 1902; notes by the author).

repainted. The glass covering exists of many small flat rectangular single glass panels. To reduce the heating costs, all these panels were replaced by coated glass jointed with mastic to improve the insulation qualities.

For the sake of the well-being of the perennial plants and trees and for the visitors' safety, restoration works could not be scheduled during winter nor during the two weeks of public opening in spring. Therefore, all work was carried out in different stages, which considerably complicated the work, follow up and coordination.

2.2 Pathology of the metal structure

The metal structure of the Winter Garden is mostly unchanged, compared to the original construction dating back to 1876. Therefore, great historical value is attached to this building and any future restorations have to be done with the greatest respect to the original structure.

The major threat for the metal structure is corrosion. By filling the joints between the glass plates with mastic, the ventilation of the inside air has been dramatically reduced. This well intended intervention resulted in more condensation on both the glass and the metal structure. Together with the very aggressive tropical indoor climate, this has lead to increased profile corrosion on some vulnerable spots (Figure 5-a).

During previous interventions, a series of profile cross-sections were reinforced by welding new parts on to the old ones, e.g. on the iron column between the side aisle and the middle dome (Figure 5-b). The tension ring at the bottom of this column was cut off from the column, steel plates were welded on the column profiles and the tension ring was welded on the added plates. The tension capacity of these welds is unknown, as the weldability of the original iron was never determined.

Some profile connections show missing rivets (Figure 5-c). These connections have to be repaired, so loads can be transferred properly.

During previous restoration works, the whole structure was sand-blasted and repainted. Nowadays, the

Figure 5. a) corroded metal profiles (2006); b) welded plates on metal column (2007); c) missing rivets (2007); d) removing the paint and the corrosion (2006).
Figure 6. Compound profiles of the arches (2007).
Figure 7. Three-dimensional structure.

Regie der Gebouwen did again some tests with special techniques to remove the paint and corrosion (Figure 5-d). The techniques were evaluated on the time it took to rub a specific profile, the grade of efficiency of the rubbing technique and the nuisance for the tropical plants inside the glasshouse. The most efficient technique appeared to be a hammering technique where needles remove paint and corrosion from the iron. After cleaning the profiles, they need to be repainted as soon as possible to avoid new corrosion.

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