Spray Finishing in a Small Shop – You Bet!
If you work in a small shop you might think that spraying is out of the question. However, that’s not the case. A knock-down spray booth will enable you to spray waterborne finishes easily and safely.
Use a Waterborne Finish
Waterborne finishes are ideal for the home shop because they don’t give off as much volatile organic compounds (VOCs) as solvent-based finishes, so they’re safer for your health. As well, they’re practically odourless, easy to clean up, and they don’t produce explosive vapours – so any fans or other ventilation equipment that you use in the vicinity of the spray booth don’t have to be explosion proof.
Equally important, the current generation of waterborne finishes are just as durable, and produce as beautiful a finish, as the more traditional solvent-based finishes. There are a number of good quality waterborne top coats on the market, including General Finishes, and Safecoat.
There are two basic types of spray systems – those that deliver air at high pressure (compressor driven spray guns) and those that use low pressure (HVLP systems). Compressor systems use siphon style spray guns, and operate on the ‘venturi principle’ – air passes over a narrow opening filled with the finish, sucking the finish out of the container, and depositing it on the work surface. This system tends to result in a great deal of overspray as a result of using turbulent high pressure (upwards of 50 PSI), low volume air to deliver the coating to the surface.
Alternatively, high volume low pressure systems (HVLP) have put professional quality spray application tools within reach of small shop owners and hobbyist woodworkers. Such systems are multi-stage turbines that deliver a large quantity of low-pressure air (10 PSI or less) 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.
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’s 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 small or home shop.
When looking for a HVLP, consider systems from the leading manufacturers.
Space is at a premium in most home workshops and few are large enough to have sufficient room to set up a dedicated spray area. That doesn’t mean you can’t spray. But you do have to think, and work, small.
The key is to use a simple take-apart spray booth that you can quickly set up when needed, and easily disassemble for storage between uses. For large projects that won’t conveniently fit into your booth, apply the spray finish to project components before you do your assembly.
You can make a spray booth out of any lightweight rigid material. Cardboard is a great choice because it’s usually freely available and can be easily replaced when damaged. You could also use coreplast, which is available from most home centers and all sign shops. I’ve had great success using large appliance boxes. Usually I place them on a pair of 24″ high shop-built sawhorses. I use a much more compact booth that sits on my workbench for small projects – jewellery boxes, display cases, drawer pulls, hand tools, and the like. If you chose to use a fan, set it on the workbench behind the spray booth, so that it vents away from the project you’re spraying. Optionally, tape a furnace filter over the face of the fan to absorb any overspray.
Keep it Simple
To keep construction simple use duct tape. Cut the cardboard panels to the size you’ll need for the front, back, and sides. 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.
Play it Safe
Even though waterborne finishes are much safer than solvent based finishes, it’s still a good idea to wear a respirator when spraying. Just as important, keep your equipment clean, especially the jet nozzles on the gun. When you’re only doing a small amount of spraying there may be a temptation to ‘clean it the next time’. I’ve made that mistake, and wouldn’t want to repeat it. Most of the time, problems with spraying come down to technique. If you’ve not done it before, take the time to practice using the equipment. Understanding how to use an HVLP system isn’t complicated – developing proficiency in using the gun does take time, and practice. But, if you’re looking for the optimal finish, then the investment of money and time is well worth it.