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  #11  
Old 11-22-2019, 11:49 AM
Reformed SeaSnake Reformed SeaSnake is offline
 
Join Date: Nov 2016
Location: Beaverton
Posts: 46
Default Build your own

I framed in a booth using 2x2’s (about 4 ft x 8 ft). Wrapped the whole thing in heavy clear plastic tarp. I use 1 box fan mounted on the ceiling on hi blowing through a filter for inlet air and a second box fan mounted on down low on the far wall on a medium setting for exit air. The exit fan blows through two filters (I replace the 1st one periodically, but the 2nd has never gotten clogged). The fan settings create a bit of cross flow and a positive pressure in the booth. I paint right under the inlet so overspray is carried down and away from the part I’m painting.

Fumes do get into the rest of the hangar but I have never had an issue with overspray. When I first built the booth I did put a cardboard panel about 4 inches beyond the outer exit filter and checked it after painting for particles, but have never found any.

Whole thing including the 2 box fans and filters was under $150.
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  #12  
Old 11-22-2019, 01:03 PM
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JonJay JonJay is offline
 
Join Date: Jan 2007
Location: Battleground
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Generally speaking, if you keep any possible ignition source, like an unsealed fan motor, out of the exhaust stream, you lesson the risk of a combustible event. Professional booths typically use sealed explosion proof fans in the exhaust stream, typically behind a filter wall. Exhausting fumes is way easier than trying to design a system to force air through the inlet.
Explosions are rare, but they can and do happen. Each person rolling their own is making a decision to either accept, or ignore, that risk. While the risk may be low, even extremely low, it exists.

I either paint in “free air” or in a properly designed booth, but that is just me.
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  #13  
Old 11-22-2019, 01:32 PM
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Zuldarin Zuldarin is offline
 
Join Date: Mar 2013
Location: Snoqualmie, wa
Posts: 347
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One more consideration for paint booths...plastic does not hold dried paint very well. I've had several variations on paint booths over the time I've been building my 9A and now the 10 and I found that the dried over-spray would flake off the plastic walls during subsequent paint/prime sessions. The plastic also seems to generate a static charge that makes it want to brush up against me every time I'm near....hence more flakes.

You might consider buying some 9'x12' canvas drop cloths from your local hardware store instead of plastic.
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  #14  
Old 11-22-2019, 01:51 PM
rockwoodrv9 rockwoodrv9 is offline
 
Join Date: Dec 2011
Location: Meridian ID, Aspen CO
Posts: 2,551
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I did a limited search and could not find a time where a home built paint booth exploded. There are some really weird accidents on the osha paint boot accident web site, but no explosions. Most of us have heard stories of how it can happen, but does anyone have first hand info?

I can verify if you do old style formica work in a basement with contact cement, make sure the water heater pilot light is off. Contact cement fumes are way different than paint fumes - especially with a HVLP gun.

I built a paint booth in my hangar with 2x2's and plastic. I had 2x2 filters on one side and 3 box fans on the other that vented out an open hangar door. I have a Hobby Air supply and I wore it, but I dont believe the air quality ever got anywhere close to being an explosion. Air exchange is the key.

On a side note, my gas ceiling heater ran the entire time and that may not have been the smartest thing.
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  #15  
Old 11-22-2019, 03:46 PM
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wirejock wirejock is offline
 
Join Date: Oct 2005
Location: Estes Park, CO
Posts: 3,448
Default Bildge blower

I built a temporary set up with a bildge blower as the exhaust. They are designed for exhausting fumes. They are 4" in diameter and dryer hose works great.
The frame is conduit hanging from the garage door frame. The sides are old shower curtains. Bildge blower is plumbed to a dryer vent installed in the shop wall. Set up is fast. It's only big enough for parts but it worked. Link is on my blog under Kitplanes Tips.
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  #16  
Old 11-22-2019, 08:18 PM
FinnFlyer FinnFlyer is offline
 
Join Date: Aug 2018
Location: Bell, FL
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I don't see how a fan (for example a $20 20" Box 3-Speed Fan) can produce sparks, IF if is left on. In other words, put it on an extension cord and switch it on/off at an outlet that is not near fumes. Don't touch the switch on the fan while it's in fumes. These AC fans are brushless, right?

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  #17  
Old 11-22-2019, 11:54 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Quote:
Originally Posted by FinnFlyer View Post
I don't see how a fan (for example a $20 20" Box 3-Speed Fan) can produce sparks, IF if is left on. In other words, put it on an extension cord and switch it on/off at an outlet that is not near fumes. Don't touch the switch on the fan while it's in fumes. These AC fans are brushless, right?

Finn
Take a motor's cover off, turn on the motor, turn off the lights and look at the brush area. constatnt tiny sparks between the brush and the armature. Easier to see on more powerfull motors. Brushless motors are expensive and not common on these size motors. DEFINATELY not common on box fans. Also, not sure that brushless is synonomous with sparkless. I beleive motors made for use in explosive areas achieve safety by enclosing/sealing the area with sparks, separating it from the surrounding air. Cooling is then the engineering challenge.

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Last edited by lr172 : 11-23-2019 at 12:02 AM.
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  #18  
Old 11-24-2019, 08:44 AM
Reformed SeaSnake Reformed SeaSnake is offline
 
Join Date: Nov 2016
Location: Beaverton
Posts: 46
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I think it is reasonable (and safe) to assume any AC motor not rated as explosion proof is producing some spark. And it is definitely worth considering the risk before building a DIY paint booth. The reason I feel comfortable using mine is that due to the airflow through the booth, there is virtually no chance of fumes getting to a combustable concentration.

The typical 20” box fan has an un-restricted flow rate of 1000 to 2500 CFM. Mine are at the upper end of that, but assume 10% of that flow rate due to the restriction of the filters (250 CFM). The primary VOC in the paint and reducer I use is acetone. Worst case scenario for a wash primer is about 75% acetone.

The lower explosive limit (LEL) of acetone is 2.6% (by volume). That means I would have to be shooting about 1/2 oz of primer per second (sustained) to hit the LEL. I don’t get anywhere close to that flow rate of paint.

At that airflow rate though, my booth is nowhere close to laminar flow. It is positively “breezy” in the booth, which is probably not as good for finish quality, but hey I’m just shooting primer anyway, mostly on surfaces I’ll never see.
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  #19  
Old 11-24-2019, 05:46 PM
JDA_BTR JDA_BTR is offline
 
Join Date: Dec 2013
Location: Baton Rouge, LA
Posts: 887
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Lots of engineers on here....
Lets say that I did want a 120V sealed motor blower. With a high CFM. cheap of course..... Anybody got any good ones in their bookmarks?
Ideally it would have an outlet to a 6" exhaust pipe outside.
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  #20  
Old 11-24-2019, 10:38 PM
JDA_BTR JDA_BTR is offline
 
Join Date: Dec 2013
Location: Baton Rouge, LA
Posts: 887
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EC motors are sealed.... found this:https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Marketed to growers, not builders, eh?
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