The most effective way to apply a finish smoothly and evenly is by spraying it. However, the process releases toxic and some times flammable substances into the air. A properly constructed spray booth (below) will contain the spray and vent it to the outdoors.
A Three-Sided Room: An effective spray booth is typically designed as an open-ended rectangle equipped with a powerful, specially designed exhaust fan at the inside end. The fan draws fumes through a filter and sends them outside; the filter traps drifting spray. Before committing yourself to a design, check local codes; also check how a spray booth will affect your home insurance. The size of the booth and the fan can vary, but always locate them at least 20 feet away from any open flame such as a furnace or the pilot light of a water heater. Situate the booth so you can vent the fan through a window opening in an exterior wall, with no buildings, bushes, or other barriers on the outside closer than 6 feet
Expelling Bad Air: The exhaust fan and its filter are the most important components of the booth. Choose a fan designed especially for spray booths, with a motor and drive belt shielded from the air passing through the fan duct. To cover the opening in the vent wall, buy a special paint-arrester filter. Your fan supplier will have a round- to-square adapter duct to connect the square filter to the round fan.
TOOLS:
- Plumb bob
- Carpenter’s square
- Tape measure
- Hammer
- Circular saw
- Carpenter’s level
- Saber saw
- Screwdriver
- Electric drill
- Caulking gun
MATERIALS:
- Plywood ( ¾”)
- 2 x 4s
- Common nails (3”, 3 1/2”)
- Wood screws (3/4”, 2” No. 8)
- Masonry nails (3”)
- Exhaust fan
- Fan shutter
- Duct adapter
- Filter frame and filters
- Fireproof wallboard
- Wallboard installation materials
- Caulk
SAFETY TIPS: Wear goggles when nailing, operating power tools, or working with finishes and other chemicals. When spraying a finish, don a dual-cartridge respirator.
Anatomy of a spray booth.
Confined by partition walls to one corner of the shop, an open-ended spray booth has walls and ceiling covered on the interior with fire- retardant wallboard. A space between the back partition wall and the exterior wall allows an exhaust fan to be mounted so its motor is isolated from the booth. The air compressor is positioned outside the booth. Explosion-proof light sockets masked by wire or plastic baskets provide overhead lighting, and all electrical switches and outlets are mounted outside the booth. A fire extinguisher is placed on the wall near the opening. The revolving platform at the center of the booth allows the user to remain upwind of the spray.
BUILDING THE SPRAY BOOTH
1. Installing the exhaust fan.
• Cut a backer board of *-inch ply wood to fit the window opening. With a saber saw, cut a hole in the backing to match the opening in the fan casing.
• Fasten a 2-by-4 mounting block with 3-inch common nails to the window sill flush with the outside edge of the window stool.
• Position the fan’s mounting flange against the backer board , then secure it with 3/4-inch No. 8 wood screws.
• To attach the backer board to the mounting block and to the window sash, drill pilot holes, then fasten it with 2-inch wood screws.
• Insert the round end of the round-to- square duct adapter into the fan casing, and install a fan shutter outside the window to keep out cold air and rain.
2. Planning the partition walls.
• Place the fan assembly in the window, then drop a plumb bob from the duct adapter to the floor 2 inches from the front edge of the duct; mark the point where the plumb bob meets the floor.
• Repeat the measurement on the other side of the adapter, then draw a line connecting the two points and extend it the desired length of the vent wall. Checking with a carpenter’s square, draw a second line perpendicular to the first to mark the side wall.
• Cut two 2-by-4s to serve as top and sole plates for the vent wall and lay them side by side on the floor.
• On the plates, outline two 2-by-4 studs to frame the fan duct at each plumb-bob mark on the floor. Mark off additional stud positions along the plates at 16-inch intervals.
• Cut top and sole plates for the marked side wall, and outline stud positions at 16-inch intervals along the boards. Then cut 2-by-4 studs for the vent and side walls 3 inches shorter than the floor-to ceiling height.
3. Raising the partition walls.
• With 3 nails, fasten the studs to the top plate of the vent wail at the marked outlines, driving two nails into each stud.
• Place the outside edge of the vent wall’s sole plate along the line on the floor and nail it in place with 3-inch masonry nails.
• Raise the top-plate-and-stud assembly into position, then nail the top plate to the ceiling joists and toenail the bottoms of the studs to the sole plate at the marked outlines. Check with a level as you go to keep the wall plumb.
• Assemble the side partition wall in the same way. At the end that will connect to the vent wall, fasten 2-by-4 nailing blocks at the top, middle, and bottom of the outside stud, then fasten a second stud to the blocks.
• When the side wall is in place, nail the end stud of the vent wall to the nailing blocks of the side wall.
4. Completing the walls and fan assembly.
• Frame the top and bottom of the fan duct with 2-by-4s, nailing them into place between studs. Drill clearance holes through the duct’s flange and fasten it to the frame with 3/4-inch wood screws.
• Install fire-retardant wallboard on the inside of the partition walls and over other combustible surfaces, such as exposed ceiling joists. Caulk the joints between wallboard panels to make them airtight.
• To install the fan’s filter assembly, screw the metal frame for the filter into the opening in the vent wall flush with the inside edges of the framing studs. Then snap the filter grid into the filter frame, insert the filter material, and snap in the two retainer rods that hold the material in place.
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