Recirculating Air Spray Booth

The construction of this spray booth happened out of necessity ,

I am responsible for the design and construct all the cabinetry for our custom built homes ( we build on average 4 to 6 homes per year ) and I was sending all our finishing out to a spray shop ( the only one in our area ) the problem that arose was that getting our finished pieces back when we needed them . Sometimes this would delay our completion, then the finishing company had some internal problems, which meant they were unable to take on any new work.

After a lot of research it became evident that because of the cost of a commercial spray booth and the shop area required that purchasing a booth was not practical for our present space. Because of our location a conventional booth would require us to have a make-up air system to heat the incoming air that would be exhausted out, another added expense.

IMPORTANT NOTE *****

I decided that we would only be using waterborne lacquers for finishing and no solvent based products. Waterborne products are more environmentally friendly, safer, and non toxic. Which meant two things :

1. That flammable vapors and fire suppression would not be an issue.

2. I would be able to recycle the air providing I could remove all the contaminates.

Today’s waterborne finishes are comparable with solvent based products; they just take a little longer to dry. And another deciding factor for using a waterborne lacquer was that there is very little odor, compared to the toxic gases given off by solvent based products ( grey cell killers and I need all that I have left ). Just because there is less odor, you still require a proper spray mask while spraying.

It should also be noted that the design of this spray booth incorporated items and material I had available to me at the time and changes to size and configuration could be used to construct a booth to fit your own needs and the materials you have access too.

As seen in the drawing,the contaminated air (paint over spray)

(A) is drawn into the first accordion type paint filter. This filter traps up to 90 % of the airborne paint on its cardboard riffles,

(B) next the air is drawn thru 5 -20’’x 20’’x 2’’ baffle filters (furnace filters ),

(C) then after the air passes thru the squirrel cage fan it is then forced thru

(D) 6 - Activated Carbon filters (to control organic vapors ).

(E) And then finally thru 5 more 20’’x 20’’x 2’’ baffle filters.

(F) The air then flows downward ( creating an air type curtain ) and then repeating the cycle with clean dust free air .

Filters A,B and E are readily available. The activated charcoal filter D was made from scratch and I will go over it's construction in a later step.

The frame for the whole unit started with 2 -9’ high pallet racks and 5 – 9’ horizontal bars. Using the steel frame would help provide enough weight to support the cantilevered upper plenum .

Once assembled the inside was lined with 3/8 ‘’plywood on the back, and 3/4 ‘’plywood on the sides. All the plywood was fastened on with self-tapping screws into the metal frame.

I made up a 3 ½ ‘’ x 6’’ piece of fir, the same length as the width of the pallet rack side, then attached a piece of ¾‘’ plywood and heavy duty casters raising the whole unit ¾ ‘’ off the ground. This makes the whole unit movable should it get in the way of our shop door.( I ended up adding a third wheel to each side and a support screw to bear the weight once it was in position)

I then built a 20’’ deep base ( the width of my squirrel cage fan and furnace filters ) x 11” high along the bottom.

Using the height of my card board baffles,( 36’’ clearance on the bottom and 18’’ on the top). the filters are held in an upper and lower U shaped channel, ( solid stock with 1/8'' masonite strips on both sides ).

The upper filter is just a 36'' filter cut in half down to 18''.

I then constructed a framework that would hold my 5- 20’’ x 20’’ x 2’’ furnace filters, and then mounted it horizontally across the unit.

The squirrel cage fan was then attached to ¾ ‘’ plywood. ( back, top and front with a hole cut out for the exhaust ) Then the fan unit was mounted above the filter framework.

Note that the 1hp motor was mounted above the fan and a fan belt connected the two thru a slot in the plywood.

Then I installed the two sides of the upper plenum ( 3/4'' x 16'' x 96 ) on which I routered out 3 -1 1/4'' x 16'' slots at 13 degrees ( these are for my charcoal filters ).

Next were cleats for back support so that I could enclose the fan, along the face (3/4'' ply), and on the top (3/8''ply).

NOTE: The face pieces were just screwed in place should I ever have to get access to the fan.

Next came the box that would hold 2 - 4' - 2 bulb fluorescent lights ( 8'' wide 4'' deep to fit between the two upper plenum sides ) .There is a piece clear glass to protect the fluorescent bulbs. ( removable and held in place with a small rabbited molding )

I added a two sided divider in the middle that matched the grooves for the charcoal filter, and then connected them with U shaped pieces for the filters to slide into.I then attached 1/4'' MDF ( maximum density fiberboard ) between the bottom of the filter and the top of the filter below ( this forces the air to go thru each charcoal filters )

Next came another horizontal framework to hold another set of 5- 20''x 20'' x 2'' filters, and then the whole plenum was enclosed with 3/8'' plywood.

I used 1/8'' white Masonite cut into strips to create the U shaped channels to hold the expandable cardboard filters in place, and to close over the horizontal furnace filters. ( removable for filter replacement )

I made two doors out of 3/4'' plywood that has a white melamine finish on it, that has two more 4' fluorescent fixtures (mounted in a box on the outside of the door. with a piece of clear glass to protect the bulb from over spray).

The doors are held in the open position with small barrel bolts, and in the closed position with a commercial suitcase latch. The lights were wired into a switch on the side of the unit and the 220 volt fan motor just had a long cord with a plug on the end.

The first step was to make enough activated charcoal (6 + pounds) If you are uncertain what is the difference between activated charcoal and charcoal, it all comes down to the available surface area on the charcoal particles that can absorb odor. Activated charcoal has something like 2700 times the available surface area compared to charcoal, which makes it so good for purifying both air and water.

For me to go into how I made it is another whole Instructable. It takes a surprisingly large amount of work to produce any large quantity. Next time when I have to replace it I will look into purchasing it in bulk .

The actual filters were a two piece wood frame that has a piece of a 3/8'' rain screen ( a material used in construction to allow air movement under the exterior siding ). Fastened to the wood frames the rain screen has a thin layer of fiberglass on one side to hold the activated charcoal, and a dense plastic spaghetti on the other side, this spaghetti side will hold the activated charcoal from moving around.

Once I had the 6 frames made up I spread the activated charcoal evenly on them . I made up window screen frames to cover the charcoal side ( removable for when the activated charcoal needs replacing) and the slid them into the slots in the upper plenum, then covered over with a piece of plywood ( removable ).

Now that the booth was complete and fully functional, it was moved to it's location by the rear overhead door of the shop.

I then needed to build a spray room to keep unwanted shop dust out, and that could be moved out of the way when we needed access to the rear door. Finished size 16' x 22'

I mounted two steel tracks on the ceiling (12' high ) that would have rollers attached to a heavy duty white tarp. The door section was made out of 2'' x 4'' and 3/8" plywood . The whole door section slides in the track as well.

Above the door is a box with a filter that holds a construction heater that blows warm air into the room. On the ceiling I mounted two house type ceiling fans that would both push the warm air down and also create air movement to aid in speed of drying the water borne finishes.

Because the heater is blowing air into the room and there is no exhaust air going out, the room is under a slight positive pressure keeping any unwanted dust from entering the room.

The last step was to build 4 mobile drying racks out of plywood and 1/2'' electrical conduit and some solid stock.

We purchased a commercial high pressure - air assisted unit that you can see mounted on the white movable cart. Having the proper spray equipment ensures a better finish.

What you see on the racks is the first job I sprayed ( teak veneer doors and drawer fronts , sprayed with clear waterborne satin lacquer ) and it turned out better than I hoped .

This is my very first Instructable and I hope that my explanation isn't too confusing. Any unique projects I do in the future I will try to document them with more detail.

Like most of the things I make and do, I enjoy the challenge, the problem solving ,and the fun of doing it for yourself.

I have believed all my life that I was always the laziest guy in the room, because if there was an easier or quicker way to do something, I was going to find it !

I have done my fair share of spraying over the years in several different booths, and surprised myself with how well this worked to control the over spray and dust control . The [air curtain effect ] prevents any dust from entering the booth area. As for the odor, I leave the booth running the whole time and have had people walk into the room while I was spraying, and said the smell was negligible.

I did not keep an accurate list of the materials used in this project, and like I mentioned at the start , the purpose of this Instructable was to show how a recirculating air booth works , how I constructed it ,and the materials used. Should you attempt to build your own booth your list of material could be completely different than mine depending on your own design, and what you have available.

The entire build took about about 6 -7 weeks, ( mostly by myself and my lead (only) shop hand ), but now we can do all of our own in house finishing, saving time and money .

One Big Massive Tool to get the job done.

CHEERS!! Thanks for your support and votes .