Cheap 'n' Easy Spray Booth:
This is a tutorial on building (like the name says) a "cheap 'n' easy" spray booth suitable for priming, sealing, basecoating with aerosol sprays, and even airbrushing. I am simply providing step-by-step instructions, and am not to be held responsible for anything that may happen through the use of a spray booth such as this indoors, i.e. toxic exposure to paint fumes, exploding furnaces, or a light dusting of primer on someone's antique furniture. (Consider yourself warned and myself absolved - nothing says "bad karma" like feeling responsible for someone else's fiery, explosive demise!) Also, many thanks to Alf from the RelicNews Forums for the original inspiration!
With that out of the way, here's the materials:
Here's a picture of the first spray booth I set up myself (it saw about 4 years' worth of frequent use):
I would suggest that you set your spray booth up in a well-lighted, well-ventilated area such as a garage. I would also suggest that you raise the overall level of the booth to a comfortable height to allow for easier spraying - my first homemade spray booth was at roughly floor level due to space considerations, but a small stool underneath gave me enough clearance to easily see all areas of my figures when spraying whilst sitting on the floor in front of it. My new booth is set back on a shelf of my painting desk, so I don't need to hunch over to see!
To start, cut a squarish piece of microfiber filter a little larger than you actually want the opening at the back of the box to be - try to make the hole reasonably large, as the whole point of this setup is to remove as much of the excess paint vapors from the open air as possible. The next step is to cut a hole about 1" or so smaller than the piece of filter in the back of the box, relatively centered behind where you expect to do the majority of your spraying. Make sure to leave a reasonable border of cardboard for the filter to sit flush against on the back of the box.
For reference sake, this is what microfiber filter looks like in its natural state:
Next, tape all the seams of the box so as to prevent excess paint being sprayed from escaping out any holes or crevices - ideally, you want as much paint as possible to be drawn towards the filter when using the spray booth. Taking your plastic bag, cut a hole in the opposite end of the opening, or, alternatively, cut the length of the bag down to a more manageable length - depending on the size of the bag, you might want to cut slits at the end so it opens neatly into four "flaps." The purpose of the bag is to act as a funnel between the hole at the back of the box and the nozzle of your commercial-grade vacuum.
The tricky part now is to tape the sides of the filter down to the back of your booth over the cut opening so that there are no gaps and the filter sits flush and overlaps the hole on all sides - with mine, I used overly long strips of duct tape on all four sides and made sure they overlapped at the four corners around the filter. (The reason I used duct tape as opposed to packing tape is for ease of removal when I next need to change the filter or bag.) The filter doesn't necessarily need to sit into the opening, but the edges do need to be airtight against the box for the next step.
For the final step with the box, tape one opening (likely the largest) of the bag over both the hole and the filter from the back of the box. As can hopefully be seen from the picture, I made a similar overlapping square of tape around the mouth of the bag against the box - what you can do is tape down a side and then trim off the excess bag sticking out with a pair of shears. I also taped over the first layer of tape holding the bag down so that the second layer of was sticking, at least partially, with nothing but cardboard underneath - this is to prevent the tape and bag from peeling away from your booth from the weight of the vacuum hose, which could be very messy if it happened in mid-spray session.
For the sake of a snug fit, you will want to taper the bag via wrapped duct tape so it fits tightly around the nozzle of the vacuum. With my box, I made a "collar" of sorts to fit around the nozzle of the vacuum - although this is actually an extra shop vacuum I have, it's occasionally useful to be able to separate the vacuum from the attached spray booth if I need to use it for anything else. One way to make the collar is to wrap a length of duct tape around a jar or bottle with the sticky side facing outwards, hold that inside the open end of the bag, mash the end of the bag around the tape, and then wrap another length of tape or two around the outside of the bag end. The tape on the outside serves two purposes: it maintains the shape of the collar so it fits the nozzle of your vacuum snugly, and it also holds the nozzle in place to prevent it from collapsing inwards when suction is turned on. (Don't make the same mistake I did and use a bottle with a slight "lip" around it - the inner ring of tape was tight enough that it wouldn't fit over the lip in trying to get the bottle out, and I ended up having to undo the entire taped-up bag!)
My first spray booth was set up on the floor and fairly low, so I used a length of wood to prop the hose up so the mouth of the nozzle sat at roughly a right angle to the back of the filter inside the bag - it gets better suction this way. If you have the entire setup on a shelf or something, this prop might not be necessary. I can virtually guarantee you will need to play around with the placement of the vacuum nozzle the first few times, as it has a tendency to either suck in the bag or stick to the filter - as you can imagine, neither situation is ideal for drawing off paint fumes, and a total blockage with the vacuum running will kill the motor. With enough adjustment and a good prop, you should be fine - just remember the ideal angle is about 90° to get the strongest draw of air toward the filter of your booth. If you're really cramped for space or your vacuum continually misbehaves by trying to eat the bag, I might suggest buying an extra-wide funnel of a large enough diameter to cover the filter and hole in the back of your box entirely, and with a narrow enough spout to fit inside the nozzle of your vacuum hose. The spout of the funnel will stop the nozzle of the vacuum hose from collapsing inwards towards the filter when suction is on, and the wide mouth of the funnel will feed fumes towards the vacuum hose nicely.
Hopefully this is all pretty self-explanatory, but let me add a few parting thoughts. The vacuum is used whilst spraying to draw excess paint and fumes towards the filter and interior of the box - ideally away from yourself and the area around where you spray. To do this effectively, you need a pretty strong vacuum (mine is 3.5 horsepower) - the stronger the suction, the less airborne paint and fumes end up in places you don't want it: your lungs, your parked car, or nearby sources of flame.* The micro-fiber filter is there to prevent the airborne paint particles from clogging up your vacuum itself: you will ruin a perfectly good vacuum if you skip using some sort of ultra-fine filter material or if you fail to change the filter out when it starts to become clogged with repeated spraying. For the sake of brain cells and your overall health, only spray in open, well-ventilated areas and not anywhere near open sources of flame: paint fumes can easily build to toxic levels in enclosed spaces; you can kill off massive amounts of brain cells as chemicals are absorbed fairly readily into the bloodstream via the lungs; you can cause an explosion if allowed to build up anywhere near a source of flame or heat - this includes the pilot lights of furnaces and water heaters, cigarettes, and space heaters.