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Retrofitting Steel Storage Cases: Installing New, Improved Gasketry


Retrofitting old style steel museum cases with new improved gaskets is an economical and effective way to deal with the inadequacies of these older cabinets. By installing silicone sponge gasketry, a well-sealed cabinet is created which affords protection from the fluctuation of relative humidity as well as creating a microenvironment which does not allow the entry of dust, gaseous air pollutants, insects, vermin and light.

In the old style cases, two types of gaskets have been predominantly used (Fig. 1). These gaskets can easily be replaced and an improved door seal can be obtained for very little cost. Older storage units containing wood, however, are not acceptable, and should not be re-gasketed.

Figure 1. Example of a steel storage cases that can be used with this system.

The more recent polyurethane foam gaskets have been shown to deteriorate readily, primarily because of oxidation or exposure to ultraviolet radiation; they give off volatile substances as they deteriorate. These foam gaskets lose their resiliency and structural integrity in approximately 2-5 years, at which time they crumble and cause the cabinet to lose its seal.


Toby Raphael
Division of Conservation
National Park Service
Harpers Ferry, WV 25425 USA
Tel (304) 535-6139
Fax (304) 535-6055

Donald R. Cumberland, Jr.
National Park Service
Curatorial Services Division
Harpers Ferry, WV 25425 USA
Tel (304) 535-6072
Fax (304) 535-6055

Photographs: Julio Gisbert
and Rosa García-Perea

Publication: 1992



In order for a cabinet to provide the preservation features mentioned above, the gasket that lines the door jamb must have special characteristics and be installed correctly to form a seal against air and particulate infiltration.

The following are instructions for retrofitting a cabinet with a high quality, silicone sponge gasket in seven easy steps.

Materials Tools Supplies

  • Cellular silicone sponge (polydimethylsiloxane) gasket, low or medium density with acrylic adhesive backing
  • Denatured alcohol
  • Metal file
  • Mineral spirits
  • Single-edge razor blade or utility knife

For filing metal cabinets

  • Dust respirator
  • Latex gloves
  • Safety goggles


  1. Order and purchase the required quantity of cellular silicone sponge gasketry (11 linear feet is generally enough per single cabinet, 36in H x 29in W x 32in D, at approximately 2.00 U.S.$ per foot, 1992 prices). The gasket should be 1/8 – 3/16in thick and 1/2 – 5/8in wide. The gasket should have an acrylic adhesive backing.
  2. Mechanically remove the old gasket, using mineral spirits, if necessary, to dissolve the adhesive.
  3. File and sand the surface as needed to make it smooth and flat, especially at corners where welds may protrude above the flat metal surface. When filing and drilling metal cabinets, wear latex gloves, dust respirator and safety goggles.
  4. Wipe the surface with alcohol for a final cleaning.
  5. Before installing the new gasket, pre-cut the four gasket strips slight 1/4in longer than each dimension needed to compensate for any future shrinkage. Cut the corners at a 45° angle to insure better fit at the corners.
  6. Set the gaskets into place making tight butt joints, and being sure to adjust the gasket to meet at corners neatly. The gasket should sit to the outside of the door stop (also called the door jamb).
  7. The door fit will generally be tight. However, if the door fits too tightly to be closed, minor door adjustments can be made as follows: the latch side can be adjusted by filing the up-and-down latch bolts or latch holes; or the hinge can be adjusted by bending the hinges slightly. The hinges can be bent outward by placing a screwdriver or similar object in the fold of the hinge and closing door.


In some of the earliest cabinets, gaskets were made of felt impregnated with such poisons as arsenic. The felt was intended to kill insects that ate through it in an attempt to enter the cabinet. These felt gaskets pose a potential health hazard to staff and therefore should be carefully removed. Wear latex gloves, and a respirator with an organic vapor/high efficiency particulate filtering cartridge. Clean up all felt and dusty residue, seal in a jar or can, and label clearly. The felt must be disposed of as a toxic waste.

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