Mildew in the Library stacks

At the beginning of May 2011, active mildew was discovered in the second phase of the stacks. This section of the stacks in the basement was immediately declared ‘out of bounds’. Staff and users were informed. Lending from this part of the collection was immediately halted. Returned books from the affected area were packed and stored separately from the rest of the collection. Humidity and temperature measurements revealed a high level of humidity. Three dehumidifiers were installed to bring humidity down to an acceptable level. DocumentenWacht, an external specialist company, was called in to assess and advise on the situation.

Their advice confirmed that the appropriate measures had been taken. We were also advised to conduct an architectural survey and mould testing, and the company gave advice on storing and cleaning the collection in the area concerned.
Further investigation showed that the mould type did not constitute a direct risk to the health of staff.

The architectural survey revealed that there were problems with the rainwater drainage – water had penetrated the cavity wall and other sections of the building. These problems were discussed with the architect of the University Services Department and subsequently resolved.
The architectural problems were dealt with by the University Services Department. The lead flashing in the cavity wall was repaired. The water drainage in the inner courtyard was improved. The soiled green glass was removed and roofing (of the section containing the stacks) was restored where necessary. Drainage has improved. The structural work is now complete.

The mildew has stopped, due to the dehumidifiers. The mildew has now turned to dry powder. The area has been cleaned by hand, in particular the books and shelving. Returned books from the affected part of the collection, which had been packed and stored separately, have been cleaned and returned to the stacks. The cleaning work is now complete.

The filters in the ventilation and air-conditioning systems have been replaced. While this was being done, it was discovered that two valves were set in the wrong position. This has been corrected, and the temperature in the affected area has improved as a result. This work has also been completed.

The problem has been dealt with. The remaining question is how to prevent mildew in future. The advice is as follows:

• It is important to monitor temperature and humidity. This is now done by staff working in the stacks. Temperature and humidity are measured and recorded every day. The University Service Department is looking into the possibilities for the remote monitoring of temperature and humidity. This investigation will be completed in 2012.
• Dust. Keeping the amount of dust to a minimum is essential in preventing mildew. Quotations have been requested for cleaning the stacks.

The quotations are for the University Library stacks and the stacks at the Zernike Complex. After decisions are taken on the quotations, a policy will probably be formulated for the cleaning operation. The work will be completed in 2012.

Albert van der Kloet
Head of Internal Servicesk