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Records Advisory: Salvaging Moldy and Contaminated Records

Dealing with Mold-Affected Documents

  • When papers have been soaked and then left for several days, they will often mold.
  • Wet paper records can be frozen to halt mold growth. They can be held indefinitely while frozen. (It is possible instead to air dry damp records. This is usually only recommended for small quantities of papers that have not yet begun to mold.)
  • It is recommended that frozen records then be vacuum freeze dried. This specific procedure removes the frozen water without it going through the liquid phase and is the most effective way to dry frozen records. It is not the same as simple freeze drying.
  • It should be noted that freezing does not kill mold. It suspends mold growth for as long as the material is frozen. Therefore, mold-affected papers would still need to be treated after freezing and vacuum freeze drying are completed. Residual mold can be cleaned off in a separate step by vendor staff wearing protective gear.
  • Do not use the following drying methods for documents: desiccant drying, dehumidification drying, thermal drying, or vacuum thermal drying. These will all harm the paper.
  • The following drying methods will not harm the paper but are not recommended: thermal vacuum freeze drying (which costs more than vacuum freeze drying), or simple freeze drying (which may be used for very small quantities of papers, but requires them to remain in a freezer for months longer than vacuum freeze drying and is therefore costly for large quantities).

Dealing with Contaminated Documents

  • Papers may also be contaminated by the contents of the water they were exposed to.
  • Papers that have been soaked in muddy water will still have dried residue on them, possibly in addition to the mold, after freezing and vacuum freeze drying.
  • If there is reason to suspect that the water contained biological contaminants (for example sewage), then sterilization is recommended. This must be carried out by a qualified vendor.
  • The two sterilization options for document holdings are: fumigation with ethylene oxide, and gamma irradiation. They are both in use though they are both still being studied; expert opinion about them varies.
  • Note that both methods require the materials to be dry prior to treatment. Both methods leave a residual odor in the paper.
  • Papers treated with ethylene oxide need to off-gas for at least a week before being returned to storage.
  • Papers treated with gamma radiation will probably be somewhat weaker as a result. Consider the intrinsic value of documents under consideration for this treatment.

Vendor Services

It is important to discuss options and expectations with vendors, and to obtain clear explanations of proposed procedures. The terminology used by vendors can vary. It is important to specify freezing, vacuum freeze drying, surface cleaning, sterilization with ethylene oxide, or sterilization using gamma irradiation, in any contract negotiated with a vendor.

For More Information

For more detailed records-related recommendations, please see the National Archives and Records Administration's webpage.

New York State Archives staff is available to provide advice on recovering records and archival material. Please contact us at (518) 474-6926 or at

Re-issued 11/7/2012