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Homebrew paint booth questions

#1
I need to fix a temporary booth in my home garage (separate 24x32 building not attached to house) so I can paint my old Vette and a shortbed pickup. I really don't want to deal with a thousand square feet of poly sheeting, and would like to have something that's reusable for future projects. Here's what I'm thinking, and would like to get input from you guys as to whether it'll work okay. I've got free access to all sorts of air moving and distribution equipment including a real booth fan, so the money I'd have to spend is minimal.

My plan is to build one wall on the 24ft depth of the shop using 2x4 framing and drywall and bolt the 4 ft wide sections together. Rather than trying to seal everything up and operate at negative pressure, my plan is to use an air handler to blow filtered air into the booth and use some ductwork and diffusers to supply the air to the booth. With positive pressure, any leakage at the joints of the temporary wall shouldn't be a problem. Yeah, famous last words I know.

I can't decide whether I should supply the air thru the ceiling, or if it would be better to drop a couple ducts down in the corners at one end and blow the air out more or less horizontally. Thoughts on that?? Either way, I'd fix a plenum at the opposite end to hold some paint arrestor pads and and duct the exhaust out thru a damper. If necessary, I can add a smaller variable speed fan at the exhaust end to balance the flow.

This might sound complicated for a temporary booth, but I did industrial and hospital HVAC work for 15 years, so the fan and ductwork stuff is sorta second nature. My main questions are whether a positive pressure booth is a workable thing, and if so, whether I should supply the air from above or along the length of the vertical ducts I mentioned up above.

Thanks in advance for your input.
 
#2
I made a similar booth. Worked well. Be sure to filter your supply air well and make sure it does not pull any exhaust air. I supplied air from the ceiling and exhausted down at the floor. Good idea to filter the exhaust too.

Don
 
#3
The problem with a temporary booth is storage when you want it out of the way. Understandably, no temporary booth is going to be everything you would like it to be but those of us who are hobbyists have to make compromises.

Dealing with the sheeting does not have to be a big hassle. I placed sheeting along two sides of my "temp" booth. Walls are the other two sides. I stapled the sheeting at the top closely with light cardboard tack strips 10 years ago. When not in use, I roll it up to the ceiling and use tie strings to tie it up. In that position, it doesn't exist. When I need it, I unroll it down to the floor and it makes a pretty good place to paint. Fortunately, I do have a window that provides a good place for an exhaust fan.

The bottom is held in place with short sections of 2x4's place along the rolled up surplace at the bottom

John



Here you can see it tied up out of the way.



 
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#4
I don't have much to offer but would like to ask you a question. How do you know when you have the proper positive pressure?
 
#5
I started with this:
Booth 2.JPG

The left side is a 2x4 framed wall with plastic sheeting.
Problems with this design:
1. Filter bank too small causing turbulence in the booth as air swirls back along outside walls toward the filter bank.
2. Lighting not sufficient to properly see what's going on, especially on the lower sides of the car.
3. Used 2 squirrel caged fans from old furnaces but they only put out 2400 cfm combinded.
Booth Fans.JPG

I later added 2 more fans converted this set up to a plenum style so that all four fans blow into a large box that passes through a larger filter bank:
New Filter Bank.JPG
You can see how dirty the older filters were because of poor ventilation.
I later closed in the plastic wall with drywall and added angles to the ceilings on the sides of the booth to reduce turbulence and increase lighting.
Angled Ceiling.JPG

Recently I began converting to LED lighting.
The need for good lighting cannot be overstated. I plan to add at least 4 more 8' fixtures on the ceiling and 4 more 4' fixtures on the walls.
I live in the country on 7 acres so my booth exhaust system is controlled by how far I open the garage door. LOL
With the fans blowing I lower the door enough where it will force the small man door in this picture closed. This clears the cloud out of the booth in less than 1 minute.

Hope this helps.
 
#6
I don't have much to offer but would like to ask you a question. How do you know when you have the proper positive pressure?
There's not really any correct positive pressure. As 68 Coronet said, he judges his by when it will close his man door. You could get fancy and use a manometer to measure the pressure, but that would be overkill. All you're trying to do is create some amount of positive pressure that will preclude any migration of dust into the booth. Most any amount above zero will make that happen.
 
#7
Thanks a bunch for the responses fellas. Very helpful.

68 Coronet's experience has made me rethink the way to introduce the air into the booth. My plan was to do all the air filtering ahead of the fan, but I can see now how much better it would be to build a plenum and filter at the point of air entry to the booth. The spray booth fan I have will do about 6000 cfm as it sits. Since its got a 3 phase motor on it, I'll buy a VFD so it will run on single phase and have variable speed and then I can fine tune it to have enough air flow but not too much once everything is up and running.

I picked up an Iwata LPH 400 gun with 1.4 tip and silver air cap as everything I've read says its one of the lowest overspray guns out there, and also because Shine says its a fairly slow gun. Last overall job I did was long enough ago that it was lacquer in my old JGA, so I sure don't need to start now with a hoser gun.

Re the lighting.... At my age, there's no such thing as too much light. I've currently got four 4' 2 tube and 16 4' single tube fixtures in the garage, all using 5000K bypass type LED tubes. I've also got about 50 8' 2 tube fixtures in storage at my other shop where I make a living. 8 ft bypass LED tubes have come down quite a bit in the last year, so for about 30 bucks per fixture I can convert however many of those I need to add to the booth area.

Its worth mentioning for anyone who's still using traditional fluorescents in a shop, you don't know what you're missing by not switching to LED tubes. The bypass type tubes allow you to strip out the ballast which is always the most troublesome part of a fluorescent fixture, and throw it away since the bypass tubes run on 120 volt power with no ballast. Takes about 10 minutes to convert a fixture to the bypass tubes.

You can walk into the shop when the temperature is below freezing, and when you flip the switch you have instant light instead of a bunch of sputtering and flashing as the fluorescents try to start when cold. And the light from the 5000K tubes is so white that it makes a standard cool white fluorescent look sorta dull yellow in comparison. Just be sure to buy frosted tubes rather than the clear ones. With the clear ones you have a string of bright spots along the tube since the LEDs are visible. They're both irritating to the eyes and tend to cause some weird shadowing effects that you definitely don't need around paint and body work. All that, and the LEDs cut the lighting portion of your power bill in half as a free bonus.

Thanks again for all the input and suggestions. Any other comments or do's and dont's are welcome too.
 

EddieF

Top Banana
#8
Psi gauge- how bout simple clear tubing thru wall & up a foot inside & out filled with water for diy water column.
No idea if it would work but sounds like fun experiment.
 
#9
Thanks a bunch for the responses fellas. Very helpful.

68 Coronet's experience has made me rethink the way to introduce the air into the booth. My plan was to do all the air filtering ahead of the fan, but I can see now how much better it would be to build a plenum and filter at the point of air entry to the booth. The spray booth fan I have will do about 6000 cfm as it sits. Since its got a 3 phase motor on it, I'll buy a VFD so it will run on single phase and have variable speed and then I can fine tune it to have enough air flow but not too much once everything is up and running.

I picked up an Iwata LPH 400 gun with 1.4 tip and silver air cap as everything I've read says its one of the lowest overspray guns out there, and also because Shine says its a fairly slow gun. Last overall job I did was long enough ago that it was lacquer in my old JGA, so I sure don't need to start now with a hoser gun.

Re the lighting.... At my age, there's no such thing as too much light. I've currently got four 4' 2 tube and 16 4' single tube fixtures in the garage, all using 5000K bypass type LED tubes. I've also got about 50 8' 2 tube fixtures in storage at my other shop where I make a living. 8 ft bypass LED tubes have come down quite a bit in the last year, so for about 30 bucks per fixture I can convert however many of those I need to add to the booth area.

Its worth mentioning for anyone who's still using traditional fluorescents in a shop, you don't know what you're missing by not switching to LED tubes. The bypass type tubes allow you to strip out the ballast which is always the most troublesome part of a fluorescent fixture, and throw it away since the bypass tubes run on 120 volt power with no ballast. Takes about 10 minutes to convert a fixture to the bypass tubes.

You can walk into the shop when the temperature is below freezing, and when you flip the switch you have instant light instead of a bunch of sputtering and flashing as the fluorescents try to start when cold. And the light from the 5000K tubes is so white that it makes a standard cool white fluorescent look sorta dull yellow in comparison. Just be sure to buy frosted tubes rather than the clear ones. With the clear ones you have a string of bright spots along the tube since the LEDs are visible. They're both irritating to the eyes and tend to cause some weird shadowing effects that you definitely don't need around paint and body work. All that, and the LEDs cut the lighting portion of your power bill in half as a free bonus.

Thanks again for all the input and suggestions. Any other comments or do's and dont's are welcome too.
Where are you buying the "bypass tubes"?
 
#10
I order mine from here: https://greenlightdepot.com/

As stated the bypass type allows you to use the old fixtures by just removing the ballast and simple rewiring.

They do make ballast compatible LED lights but to me dumping the ballast is the best option.

The first time I ordered the Clear tubes but they do funny things to your eyes when you look directly at them while working. Frosted seems to be much better. I moved the Clear tubes to my garage area where they work great.
 

EddieF

Top Banana
#11
And in 4 footers get at least 20w.
Like 68 said, frosted or you'll see dots after looking at them & in reflection.
I used a couple clears that uplight bounce of celing in kitchen.
 
#13
I would say yes. I did one half of the booth first and noticed I could see much better with the LEDs. You have to get the ones that have true color ratings, I think its 5000 but would have to look it up.
 

EddieF

Top Banana
#15
I got a couple different brands from amazon. Out of 20+ t8 style, 1 is flickering. All ballasts removed.
I went with 4000 cause that's pretty much snow white & its my home garage. Also got some 5000 which seem to show paint colors a bit better. Possibly scratches show better too.
4000 for kitchen.
CRI is another spec. Higher the better so they say.
 
#19
I'll say this- ballasts removed means always have 1 extra led on hand just incase.
I did (actually my father) leave most of them in fixtures, just bypassed them.
Me being in wheelchair can't. The 1 strobeing led on me might just need a twist. I tapped it but ng.
I did however mount a dozen myself down low to wooden shelf 2x4's and cheaply- bought 12 packs of tombstone ends & screwed them direct to wood. They don't get more then warm after 2hrs and only project light out front side.