Share thisConsider that a holding room is an envelope of dissimilar materials. Concrete, masonry, drywall, steel, and plastic are all just a few of the materials that are used to construct a holding room. The envelope is built using these materials. Each time these materials are joined together they create joints and gaps. In addition, mechanical diffusers, lighting, electrical, and fire protection penetrate the envelope. To control the holding room environment and cleanliness, a balloon would be a perfect enclosure. However, this is almost next to impossible to achieve - or maybe not. In visiting some vivarium facilities, I am disappointed at how inadequately some rooms are sealed. Lights, electrical receptacles, and doors are typically overlooked; sealant is applied after the fact creating sloppy installations.
One of the first holding rooms that I designed consisted of walls extending to the underside of structure above. A gypsum board ceiling butted the vertical walls with a sealant joint around the rooms; the doors were gasketed at all four sides and all penetrations were set in sealant. When the contractor first powered the mechanical system (this was before balancing the room), the ceiling lifted six inches. I could see the sprinkler heads part from the ceiling. I said to myself, “Wow, this is a balloon!” So, it is possible to create a total envelope.
Let me first introduce the different types of sealant. There are a great many sealants on the market and an almost equal number of specific properties to consider in their selection. Of these characteristics and requirements, the most important for this design purpose are those associated with the sealant’s ability to be paintable and to form a gasket. Movement, although very important, typically is not an issue once the building is tempered. Another important requirement is that the sealant be FDA or USDA approved, anti-microbial, and fungi resistant.
Latex (water-based)
• Excellent paintability
• Some meet USDA or FDA approval
• Interior and/or exterior uses
• Premium products meet ± 25% movement
• Exhibit some shrinkage after cure
Silicones
• Not paintable
• Some meet USDA or FDA approval
• Excellent UV and heat stability
• Good adhesion to many substrates
• Very good joint movement capabilities; can exceed ± 50%
• Adhesion is adversely affected by less than perfect application conditions
• Some generate electrolytic action attracting dust and dander
Polyurethanes
• Some are paintable; compatibility needs verification
• Some meet USDA or FDA approval
• Excellent movement capabilities, up to ± 50%
• Excellent bonding, generally without a primer for many surfaces
Acrylic (solvent-based)
• Can be painted
• Generally meet ± 12.5% movement
• May need special handling for flammability and regulatory compliance
• Short open time; difficult to tool
• Exhibit some shrinkage upon cure
• Often used for perimeter sealing; low movement joints