For anyone who does a lot of refinishing, a spray booth is a vital piece of equipment. The ventilation fan in a booth is important for the health of the person spraying, and it's also important for the workpiece because it prevents overspray from settling and creating a grainy finish. To finish cabinet doors, you could make do with a bench-top booth, but a full-size one isn't much more trouble to make.
The controlled environment of a spray booth should include a system for air circulation and exhaust. Most commonly, that's supplied by an exhaust fan at one side of the room and an opening in another wall to admit air. The booth also needs a light source bright enough to allow you to see what you're doing. It should have enough floor area for you to move around comfortably while trailing a spray hose behind you. Finally, because finishes are sensitive to temperature and humidity, it should include a heat source in the winter and on wet days, a dehumidifier.
The spray booth needs to be in a seldom-used part of the house or in a separate out-building, and it should be constructed next to an exterior wall so the exhaust can be directed outdoors. You may want to locate it in your workroom, but if you do, you have to completely enclose it to keep out dust, wood chips and other contaminants. If the booth is in a separate room, on the other hand, you can a simplify it. For example, it may only need three walls, and the corners of the walls may not need to be airtight.
Materials and Construction
Keeping in mind the fumes and dust created during most spray operations are flammable, construct the walls from a material that doesn't burn. Rigid foam insulation fits the bill. It is lightweight, impermeable and easy to work with. You can cut the sheets to the dimensions you need with a handsaw, and assemble them without screws or nails by gluing them together with wood furring strips and silicone caulk. Once the structure is together, make it airtight by filling gaps with spray polyurethane foam insulation.
Lighting and Exhaust
The hole for the fan should be close to a window, and a regular box fan placed outside the hole sucks the spray out of the booth. Put a furnace filter in front of the hole to control emissions. The work table can be anywhere in the space that has sufficient draft. It's usually a good idea to keep it away from the fan, however, because the air currents there can affect the spray. Do not use halogen lamps for illumination, because the heat they produce could ignite the fumes. A fluorescent fixture hanging over the work table on a wooden frame is a better option.
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