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How should I vent a freestanding spray booth?

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Discussion Starter · #1 ·
I want to build a spray booth. Lumber and plastic, easy to put up and down, with a vent. It would not be inside my garage, no space or I would spray in there. It will be freestanding. Im not trying to paint my car, I have mismatching primer on the new metal and I want to spray matching epoxy primer, maybe some eastwood rat rod flat black, so it looks presentable but still a work in progress.

There is a big hemlock tree that drops needles right above the driveway, just trying to keep those off while I paint. I already have a compressor, filter, gun and gallon of epoxy primer. I have sprayed smaller parts in my garage. Im not trying to dodge paying someone to primer my car, I just have all the necessary equipment to paint, and I have a steady painting hand and practice under my belt.

I'm reading that the fan needs to be "explosion proof". It makes sense that you don't want a motor sparking with paint in the air. What are other safe alternatives? Do I even need a vent?

Squirrel Cage Blower
I have one venting a garden. The motor is on the outside of the metal casing, where the air runs through. Would this be a safe design? They move a lot of air for a little money. A 265 cfm fan is $90.

Inline Fan
More expensive, sounds like a small jet taking off. Inline fans work with an impeller just like a procharger. Probably has some mechanicals inside where the impeller is, not sure if it would be as safe as the squirrel cage blower.

Would either of these work, or is there a risk for spark? Anyone have a home built spray booth? How do you vent it? Do you have to vent it? Send some pictures, give me your input.
 

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Good that you are cautious. Everyone should be. The house sometimes wins but the odds of an explosion are slim. We ran a woodstove in a 26 x32 for two years in a shop in 1982. But had excellent exhaust. Then we built a downdraft. The number of shops across the country not meeting code is high. Now, acetone vapors in concrete floor artwork is no laughing matter. Very explosive. The odds are much higher for explosions and it does happen. So yes, use caution by all means with your paint booth.
 

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i have done epoxy primer before where i just built a roof and 2 "walls" to block the wind. If you wet the ground around and under the car it keeps a lot of the dust off. Run the fast reducer/hardener and it will dry in a jiffy. Anything that sticks after a few minutes would just brush off when the paint dries to the touch.
 

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My car was primed and painted outside of the paint booth at the shop I had it done at. They just wet the floor down like Scott said above. Dean is right but make sure if you use the squirrel cage that the wheel runs true and does not hit the housing - metal to metal sparks there.
 

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what if you used the fan as a pressure fan instead of an exhaust fan, that way the fumes are not present at the fan motor, turning it on before you start spraying?
 

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I think if you use the fan as a pressure (blower) fan then there would be too much air stirring around inside the booth to do a decent job. You want the air to just flow over and not blow over.
 

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My neighbor used to paint in his garage using a fan to blow the exhaust out a hole in the garage wall. Of course, his at home paint booth lasted just long enough till my call to the code enforcement guy shut that business down. After talking to my neighbor, it was clear that he thought that everybody likes to smell and breathe paint fumes all day long but he learned that he was wrong. My advice is not to paint at home unless you don't have neighbors.
 

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I think if you use the fan as a pressure (blower) fan then there would be too much air stirring around inside the booth to do a decent job. You want the air to just flow over and not blow over.
Pushing or pulling air is moving.
 

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True. :yes:
How ever the air enters it needs to be filtered coming into the booth, not going out.
Positive pressure is the only way to achieve good filtration. If you rely on neg. pressure every hole in the bubble is a contamination. Every time you open the door unfiltered air will displace the clean air as fast as your fan is pulling. Micro chip factories only use pos. pressure for this reason. Having said this, I use a 750 cfm mushroom exhaust fan for my paint room (can't really call it a booth) which gives me an air change every 3 minutes and seems barely adequate coupled with the use of a supplied air breathing system. This type of fan leaves the motor out of the airstream.

Jerry
 

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Positive pressure is the only way to achieve good filtration. If you rely on neg. pressure every hole in the bubble is a contamination. Every time you open the door unfiltered air will displace the clean air as fast as your fan is pulling. Micro chip factories only use pos. pressure for this reason. Having said this, I use a 750 cfm mushroom exhaust fan for my paint room (can't really call it a booth) which gives me an air change every 3 minutes and seems barely adequate coupled with the use of a supplied air breathing system. This type of fan leaves the motor out of the airstream.

Jerry
Very true every little crack will let unfiltered air suck in if the booth is not totally sealed within.
 

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Heres a bunch of stuff I wrote up a while back. http://www.chevelles.com/forums/showthread.php?t=243936&highlight=home+made+spray+booth

My setup is a negative pressure with a cross draft, very minimal dirt to almost non existent dirt, really clean paint jobs.

But its very low air flow and using supplied air because of the fumes, but it is a pleasure to paint with it, no stress from a respirator, a little cool breeze inside the hood.:thumbsup: And you can step out of the booth into the rest of your garage and you have zero fumes, it is user friendly.

Rob
 

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True. :yes:
How ever the air enters it needs to be filtered coming into the booth, not going out.
I think if you use the fan as a pressure (blower) fan then there would be too much air stirring around inside the booth to do a decent job. You want the air to just flow over and not blow over.
Large companies filter their air going out to reduce pollutants. The air has to go somewhere. Spraying occurs 6 days a week all day long. Other companies never stop.

Positive systems. Separate fresh air intake is heated to desired temperature then forced into the booth, another exhaust fan pulls it out at at a lower rate and forces it through a filtration system before being expelled into the environment. The pressure in the booth is regulated quite accurately with these set-ups. No air is coming from any place in the shop and is not subject to temp variations controlled by the shop thermostat. The entire system is self contained. Far more advanced than a backyard special. But an adequate system can be made for shop or home. We built our own downdraft in it's entirety in '82.
 

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I want to build a spray booth. Lumber and plastic, easy to put up and down, with a vent. It would not be inside my garage, no space or I would spray in there. It will be freestanding. Im not trying to paint my car, I have mismatching primer on the new metal and I want to spray matching epoxy primer, ..........................
Albeit interesting, we're drifting off into another world here.

I wouldn't even worry about a vented spray booth myself but if you have a tree dropping needles like you said, just throw up a temporary tarp to paint under.
 

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Discussion Starter · #19 ·
Thanks guys, nice to see the thread take off. If a squirrel cage blower will work, I can easily afford a bigger one than 265 over the $600 plus for the explosion proof fan.

What kind of filter do you use for dust? Will a HEPA filter work? They make inline HEPA filters that attach to the ducting. What do you use?
 

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i used three cheap (~$15) box fans from walmart. they were setup on the intake side, with prefilters, and i used filters on my exhaust side as well. i kept the fans on low, so although there was a lot of air exchange, there really wasnt a draft.
 
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