Canadian Woodworking

Portable Spray Booth

Author: Carl Duguay
Illustration: Mike Del Rizzo
Published: June July 2007

Hand rubbed oil and wax finishes are justifiably popular, but there are times when such a finish is not appropriate. For table tops and other surfaces subject to hard usage, water or abrasive products, a modern film finish is the best choice.

This portable spray booth will enable you to spray water based finishes easily and safely, even if you have only a small workspace.

Water based finishes are ideal for the home shop because they do not produce explosive vapours and they are practically odourless. Also, the electrical equipment in your spray area or any associated fans and ventilation equipment need not be explosion proof.

Most people are familiar with the compressor driven siphon style spray guns. These operate on the ‘venturi principle’ – pass air over a narrow opening filled with fluid, and the fluid will rise out of the container and be carried in the air stream. This system tends to result in a great deal of overspray as a result of using turbulent high pressure, low volume air to deliver the coating to the surface.

Alternatively, high volume low pressure systems (HVLP), like the Fuji Mini Mite 4, or the Turbinaire, have put professional quality spray application tools within reach of the average home shop. Such systems are multi stage turbines that deliver a large quantity of low-pressure air to the spray gun. Some of this air is used to pressurize the cup containing the coating. When the trigger is pulled, this pressure forces the coating up a tube and into the air stream which then deposits it on the surface being sprayed. (see: “High Quality Finishing with HVLP”, June/July ’06, Issue #42). Transfer rates with a conventional compressor driven gun can be as low as 20% with most of the coating being lost as overspray. With an HVLP system, it is possible to achieve transfer rates up to 90%. This means less of the coating will end up in the air as overspray, making this a much more efficient system to use in a home shop.

Space is usually at a premium in home workshops and most are not large enough to have sufficient space to set up a dedicated spray area. But with this simple spray booth you can quickly set it up when needed, and easily fold it up and store it between uses.

You can make this booth out of coreplast or a similar lightweight product. Duct tape holds it together. The illustration below shows a freestanding booth with a stand on which to place a fan – this is ideal for spraying large items like furniture or cabinetry. The illustration also shows a smaller unit that will fit easily on a work table. In this case you won’t need the stand, simply set your fan on the workbench behind the spray booth.

Begin With the Stand

The stand needs to be more functional than attractive. You can make it simple, so as to hold the fan and some finishing supplies, or more elaborate, with doors and wheels to make it easy to move around the shop. Build it out of ¾” plywood or similar sheet stock.

The Spray Booth

To keep this booth light and portable, the collapsible portion is made with coreplast. This material is available from most home centers and all sign shops. Optionally, you could use a heavy cardboard. To keep construction simple we use duct tape. Cut the coreplast panels to the size you will need for the front, back and sides of the booth. The top and sides are held together with duct tape in a specific way, because the way you tape it together will determine how well it folds up. Lay the top face up on the shop floor and butt one of the sides up to it. Apply duct tape to the seam. Take the two pieces and fold them together, face-to-face, with the duct tape in the center. With the two pieces closed, apply tape to the seam from the outside of the joint. This will allow the two pieces to fold up in one direction only. Repeat the previous steps to attach the other side. “This spray booth is designed to be portable and functional.”

The Back

While you could use coreplast for the back panel, ¼” ply will add a lot of rigidity to the booth, and make a more stable surface for securing the sides. To fasten the sides and top to the back you will need to make several attachment blocks. These are relatively small and could be made from any convenient scraps left over from other projects. You will need at least four pairs – one at each corner. Drill holes in the blocks to accept dowels (½” or larger dowels work best), and use a scrap piece of coreplast as a spacer, then glue or screw the blocks to the back. Cut out a window somewhat smaller than the size of fan you will use with the spray booth.

Assembling the Booth

When it comes time to finish your project, setting up the booth is a simple procedure. Lean the back of the booth against the stand (optionally you could attach the back to the stand with bolts), and unfold the main portion of the booth. Slide the edges of the coreplast into the attachment blocks and slip a dowel though the holes (optionally drill holes in both ends of the dowels to accept cotter pins, which will help to keep the dowels from inadvertently moving out of the blocks). Place a fan on the stand (optionally tape a furnace filter over the face of the fan to absorb any overspray), and you’re ready to finish. – CWM

Carl Duguay - [email protected]

Carl is a Victoria-based furniture maker and the web editor at Canadian Woodworking & Home Improvement.

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