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CFM for paint booth exhaust fan?

atreff

Well Known Member
To those who have built their own paint booth, what do paint professionals recommend on how much air exchange is needed? I've found a 3100 CFM explosion proof fan:

http://www.sprayshield.com/

So, my question is how many air exchanges per minute do paint professionals recommend? Any ideas? I've found nothing in Ron Alexander's book, nor in Sam James Painting 101. In a booth 20'x12'x8', a 3100 CFM fan will provide 1.6 air exchanges per minute, not sure if that's too much or too little. :confused:

Art
 
Home made paint booths

I painted my "6" in my garage by installing a 2500 cfm explosion proof exhaust fan, with a paper filter frame "box" on the end of the ducted intake. I just put plastic sheeting up all around the garage walls and overhead. I installed a screen door on the small personnel door opening of the garage then duct taped on a bunch of home HVAC air filters on the outside surface of the screen door. This filtered the intake air, an allowed a sufficient air intake area without cutting down my flow too much. I believe I calculated that my air changes were going to be about 1-2 changes per minute.
I was glad that I captured my overspray in the paper paint filters before letting it get outside as to not let it get on neighbors cars or my own for that matter.
On two other topics - for what it is worth...
I installed a total of 6000 watts of light and that was still not enough - the more light the better!
I switched over to the gravity feed HVLP spray gun - which feeds off a regular air hose, instead of the turbine deal. Glad I did this too.
You absolutly need a full face fresh air supplied respirator! and nothing less!
You can see my "6" on the Centennial Homebuilt section of the EAA website under "wittman" RV-6 if you like.
If you have further painting questions, drop me an email dwittman_at_sonoma-county.org
Good luck
Dale
 
PapillonAir said:
You absolutly need a full face fresh air supplied respirator! and nothing less!

Dale,
Do you have a source for the full face air supplied respirator?

Larry
RV10 #356
 
The half mask with a hood is also acceptable. They are available in cloth or tyvex material and you can get replaceable lense protectors to keep overspray off the hood lense. I find the hood and half mask much more comfy tham the full mask. Keeps my hair from becoming the same color as my projects, too.

For a home made spray booth (10 X10 X 20 feet) I used a 20" box fan and furnace filters and blew the air into the booth. That way an explosion proof fan is not necessary, cause you do not draw fumes across the motor. I used filters on the fan and had an exit filter. Worked fine.

Roberta
 
Full Face Resp Source

I got the "hobby-air" system often advertised on the VAF site. I just got the simple one without the dual system to also drive a paint gun. I did "upsize" the system a little to allow a helper mask if needed, but turned out I did not.
I liked the full face system with a tyvek coverall with tight hood as opposed to a loose hood/head gear set up. The full face systems have tear off lenses that keep the glass clean, and the tight hood on the coverall stays with you nicely and keeps paint off hair. The important thing of a full face is that many of those paint toxins can enter your body through the eyes too.
Use what you like.
Dale
 
Where to put paint booth

Roberta and gang,

Thx for the quick replies, it all helps. I'm moving to a new house soon, and the garage is below the main house as part of the basement, not in a seperate building. It will be seperated by 5/8" drywall and all the other building code stuff for seperating garages from living areas. The ceiling will be 9' off the floor, so tons of room to circulate air around the booth and out the door.

So, when you all rolled your own paint booth out of plastic, was there still obvious paint fumes all over the place outside the plastic? Enough so that if your garage were under your house, you'd make the rest of the fam' crazy smelling the fumes? :confused:

If so, I guess I'll have to construct my booth outside in the driveway, which could mean I'll have to spend a few $100 more and buy one of those portable garages from JC Whitney, and seal that up. :eek:

Thanks again,
Art in Asheville, NC
 
do I need an explosion proof fan

I'm wondering if I really need that explosion proof fan? I am aware of and have seen fires in garages where people have been working with gasoline products, snowmobiles, lawnmowers and the fuel is the gasoline and any spark nearby is hazardous. Contrasting that to semiflammable(?) paint fumes where you are diluting those fumes with fresh air through filters is there really a cause for concern using a few of the cheap box fans? Let me know what you think.

Dave Ford
RV6 getting ready to paint
 
I've been painting in my basement garage for the last three years. The top two floors have never smelled paint during that time. How I did it was; Installed a stock box fan. Whenever I painted, I installed the fan butted right up against the window which was screened. Then I blocked off the rest of the window not covered by the box fan with plywood. Before painting I would start up the fan and run it until the paint was basically cured. The fan would suck air out of the rest of the house which would stop any fumes from seeping into the living area. I kept the door to the basement blocked open to assure a steady supply of fairly clean air. For finish painting, the doorway could be blocked with a full size filter to keep out the specs from your paintjob.

Cheers, Pete
 
Pete,

Thx for the tip. Just want to understand your setup. So, you have a plastic sheet home made paint booth to put the plane parts in. I assume that that has the usual box fan with furance filters inside to keep the dust down and vent the overspray.

And the box fan you put in the window is outside you paint booth?

Art
 
Here are some shots of my spraybooth. I made two wooden frames to hold the furnace filters. Vinyl siding "J" channels where attached to the frames so I could slide replacement filters in as they got loaded with paint. One frame was attached to the box fan and the "J" channels sandwiched the plastic sheeting to seal the whole frame, filter and fan assembly. The other frame was attached to the plastic with "J" channels to mount the exhaust filter.

I blew filtered air into the booth to provide positive pressure to keep dirt from getting sucked in. This also kept fumes from going through the fan motor, lessening the chance for a fire or explosion.

Flood lights attached to firring strips provided light on the sides and I hung several flourescent shop lights from the ceiling.

I used 4 mil plastic for the walls and attached it to the framework made from 2" PVC. I used tape, tiewraps and clips to hole the plastic in place and used a large zipper from Home Depot for the door closure.

This booth was built in our hangar, which is attached to our home. During painting, the hangar door was cracked to allow the fumes to exhaust out the hangar door. We move our cars out to keep any overspray that might escape off of them. Paint fumes did not linger and did not intrude into the house. After painting, were were able to safely close the hangar door to maintain heat during winter painting sessions (we live in Wisconsin). We had no problems with fumes or paint getting on anything in the garage/hangar. The booth kept the paint contained and the plane parts clean during painting.

I successfully painted two airplanes this way. My SeaRey was awarded "Outstanding Homebuilt Seaplane" at EAA '02.

I used a Citation HVLP unit with fresh air supply. I liked using the half mask under a hood. The positive pressure under the hood kept all paint and fumes out and I never smelled any paint while in the booth using this setup.

The whole thing cost less that 300 bucks, including wiring and lighting.

Hope this helps and good luck with your paint project.

Roberta

paint32yb.jpg


This is an overview of the booth in our hangar.

paint41mw.jpg


This is looking into the booth. The fan and filter are just fastened to the plastic with the "J" channels and the fan sets on some blocks. Keep it simple and cheap.

wingpaint11ny.jpg


This is looking out the booth. You can see the exhaust filter and the wood frame that holds it.

spraybooth5am.jpg


Here is a shot of the fuselage being prepped in the booth. You can see the zipper for closing the booth.
 
similarly...

Similar to Roberta's...this is what I used to paint an old Harley Sporter's oil tank, fuel tank, front/rear fenders, and a few other parts. Obviously too small for an airplane...but maybe okay for a priming booth.

What would I do different? (1) Would not use that type of furnace filter again. Too much restriction. That simple house fan on medium really pulled the plastic in tight. (2) Would probably put the fan on the intake side vice the exhaust side for the explosion protection. However, with the plastic booth under pressure, it sure would make sealing the door harder than with it under a slightly less than ambient pressure when the fan was on the exhaust side.

Just another data point. YMMV.

-Jim



[img=http://img297.echo.cx/img297/3522/motorcyclepaintbooth0033lt.th.jpg] [img=http://img297.echo.cx/img297/1866/motorcyclepaintbooth0020ba.th.jpg] [img=http://img297.echo.cx/img297/3170/motorcyclepaintbooth0017rf.th.jpg]
 
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So Roberta...

"I successfully painted two airplanes this way. My SeaRey was awarded "Outstanding Homebuilt Seaplane" at EAA '02."

Hummmm....

How much to paint my RV-9, in say two years?
 
thanks for all the booth tips. coming in handy right now, had a couple thousand ft. of used 1.5" PVC laying around so we're finished with the frame and working on the fan auxillary stuff etc.

mark
 
Paint booth issues

Hey guys, there are a couple of things you need to consider for these booth issues. For the CFM issue you need to consider the characteristics of the paint you are using. I have a 50 X 60 paint booth that we only have a exchange rate of 1 air replacement every 5 minutes. But, I use a paint that stays "open" for 3 hours and isn't dry to touch for 8 hours, so we never have to worry about hazing. If you are shooting in a booth and your paint skins over in 30 minutes and you still have mist in the air, you're going to haze over your paint. Check the paint dry times. For a booth as small as what you are probably using in a garage or t hangar, an exchange of 1 per minute is very good if your paint isn't a quick dry paint. Especially check clear coats, they usually dry much faster.
As for masks, you definetly need a full face, supplied air mask if your paint contains Isocyanates. Standard Organic Vapor cartridges like the 3M brand you get at your local paint supply store are inadequate as they do not stop Isocyanates. Isocyanates are also absorbed through the skin, YES SKIN, as well as the eyes and nose and mouth. So, be sure to wear gloves with the cuffs taped shut to your suit and wear a hood of some type with the neck area sealed with tape.
You can also absorb the Iso's while mixing if you are breathing the fumes directly, like when you stand up close to your paint container while stirring. The Isocyanates are in the hardener and they will be listed as Di-isocyanates or Poly-Isocyanates. These build up in your system like lead does and will cause a veritable plethora of health problems including short term issues with breathing, heart, nervous system, or even death if acute exposure is sufficient.
Also make sure you ground all parts to be painted, and make sure you groung the plastic sheeting you make your small booth from. It will build static from the air molecules being accelerated by the paint gun and will make you a smoking hole in the ground if you get a spark in a high concentration area, like, maybe your exhaust fan where all of the fumes and paint mist is being pulled to. The plastic can be grounded by taking heavy gauge stranded wire and stripping back the insulation to expose the strands,then spread the exposed srands out like fingers onto the plastic and tape them in place using aluminum metal tape and connect the other end to building ground.
The strands should be fairly long since the plastic doesn't conduct well and may build up a charge but not be able to dissipate it because the strands are too far away. This also helps keep the plastic from attracting dust because of a static build.
Keep in mind that you may not be able to feel the static if you are at the same voltage potential as the plastic, but it still may be there in other parts or even in the paint. We use an electro static system that requires all parts to be grounded and the paint is charged and thus drawn to the parts. So the seat of the pants method doesn't apply here when it comes to determining static build.
 
Paint Booth CFM

Most paint booths have 100-150 linear ft/min.
OSHA requires at least 100 linear ft/min.
The easy way to calculate this is by taking
the the total sq. ft. of your intake or exhaust filter wall
and multiply by 100.(Most booths have filters covering 2 whole walls)
This will give total cfm requirement to meet OSHA regs.
You can probably get by with 50 linear ft/min. but if you
go less than that you'll get alot of paint hanging around
and messing up your finish.

Also there is a risk of explosion depending on your paint.
I would never paint without an explosion-proof fan!

You can get ideas on paint booth designs at our website:

www.SprayShield.com

Chuck Stuhrenberg
RV-7A Flying
N180WC
RV-10 In the works
 
Since I paint RVs for a living I'll add my .02. I don't have any specifics in front of me so I'll give a general guide line. You want your fan to pull your overspray out of the booth but not so powerfull as to run the risk of pulling dirt into the booth and onto your paint. This not as big of a concern in purpose built paint booths as they are generally sealed pretty good and have intake air filters. Temp booths like the one shown in the earlier post and basic hangers used for painting can leak more unfiltered air. This can increase the trash in your paint job. That's not to say they are bad. Great results can be had. I've painted Lear jets in a booth made of PVC pipe and plastic sheeting, suspended from the rafters of an old crappy hanger.

:)
 
How did you fasten the zipper

Roberta,

The booth looks like a great creation! You could probably offer plans!

How did you fasten the zipper to the poly?

thanks, and I think I'll copy your design :)

Tim Ribble
 
Paint booth 101

I've been painting cars for 25 years using regular fans to exhaust the air. I've never had an explosion which is not to say it isn't possible. Every few years the fans die but the Home Depot aviation dept has lots of fans.

Exhaust vent the room at the bottom in one location and chest height at another location so you exhaust airborne and particles dropping to the floor.

Dampen the floor, use a/c filters for incoming air, hang a wet towel 6" away & in front of the vented air to capture overspray so that your neighbor's cars are not painted, make sure the compressed air goes thru water and oil filters, place your regulator & final filter at the gun, work with hvlp, enjoy.

Practice, practice, practice before squirting material. Wear a forced air, full face mask even when mixing materials & gloves. Don't believe the baloney about if you can't smell it, it won't kill you.

I like the Sharp Finex 300 gun which paints at 29lbs at the gun. Gets great results. I use a 1.8 tip for primer and 1.4 tip for base & clear. It's better than my old $300 Devilbiss.

You cannot have enough lite so you can see the glare as the paint or primer lays down. In addition to 13 overhead lites I welded a base to a Home Depot 48" fluorescent lite so I can stand it up and direct the glare down the side of flat panels. If you cannot see the paint build up on the panel, you cannot flow the right amount of material. It will either be too dry or too wet and sag.

Don't forget to allow for flash time between coats. Too many jobs are ruined by inadequate flash time.
 
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