air flow

T

Treeslayer

Mike
i have a question on air flow while painting. my shop is 30x50 and not air tight at all. i have a 36" exhaust fan on one end and an entry door on the other.
with the door wide open its almost a wind tunnel. great for fumes, but is this too much? with the door closed the fan is defiantly more limited, but it is still pulling air. which way is better?
i could prop the door so its just cracked. suggestions?
 
The more air flow, the more dirt/dust etc.
Also, to much air flow can cause the top coat to dry to fast
trapping the solvents beneath which causes all kinds of problems.
I paint with as little air flow as possible.
 
ideally a spray booth will move air @ 75-125 feet per minute. not cfm. thats the speed of the air moving through the booth. if your not in a booth then thats a bit harder to figure out because air doesnt move evenly in a shop. its usually a swirly mess that picks up dust like jim mentioned. ultimately though, if you were in a long room with exh on one end and intake on the other then those are the #'s to shoot for.
 
hmm, im hearing dust will be the issue, and i have no doubt. wonder how i can figure out whats enough? with the door shut, she will draw a lot through the eves, which is not ideal since they are 12' up.
 
I am here at the boat factory and they just happen to be tenting up to spray a small 37 hull. Here are some pictures how they do it. This is pretty much industry standard when spraying anything on a boat.


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For a fan they use these small inline exp proof fans prob 12” dia and you tape a disposable clear plastic duct to it. Prob 4mil clear plastic and it comes on a big roll.
 
I painted my car in my 30x50 with a 36 inch fan. My shop is spray foam insulated. I cracked my 12ft roll up door about 8 inches. And kept the walk in door closed. It moved air. Still got foggy when spraying clear. It was alot to spray. Complete car in pieces. You can forget about not getting dust or nibs in the finish. It's going to happen. Your best approach is to spray early in the morning. Use good quality tack rags before basecoat and in between coats. And before clear. Keep your hose clean and say a prayer.
 
I’m all for as much air flow as you can to clear overspray out. As mentioned, dust is invitable and is a lot easier to sand out than too much dry spray or texture because you couldn’t see what you were doing or had too much overspray land in your paint.

Also, don’t overplay how much of an issue dust is. I’ve painted an entire camper outside before and even that had hardly any nibs in it.

That was actually one of the best spray jobs I’ve done. Perfect light and no overspray fog.
 
oh, i know its not gonna be a perfect job. its gonna have some dust.....i always seem to catch a damned fly in it no matter what.
no clear, shes gonna get ss black. we might not get the ss on until spring, depends on temps, but i need to get it in epoxy.
silly question for y'all......water in the air hose. my air cooler is now working great, dry air comes out the last trap every time i check it. but there is moisture in the hose. i have other hoses that should be dry, but i never really considered the hose as a problem until now. i see that it is. i can use a fresh hose to paint with, but i would rather not have it in any of hoses. whats the deal here? maybe rotate the hoses......hang um up high to dry?
feel like im talking about laundry........
 
I haven't had that issue as if you blow enough dry air through it it eventually removes all the water or dries it out. Sometimes I will set the hose out in the driveway on a really hot or sunny day to get it hot and evaporate out the water. You need to have any couplers removed to the hose so it's open on both ends. Or you could turn your oven on low (less than 200F or whatever temp rating the hose has on it) and coil it up in the oven to dry for 30 min or so.
 
I've used this lay flat ducting connected to a 12" exhaust fan to blow the fog out of my garage and deep into my backyard.
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Jim, do you know what plastic was used to may that boat tent?
 
Thats the same ducting. Its the same company that makes the fans as well. The white plastic i believe is just shrinkwrap plastic for boats.
 
ran the fan with the doors shut. plenty of draw, no over spray cloud at all. i am some what surprised, as strong as this stuff smells, it was not bad at all an hour after spraying.
 
My experience over the years when I have had to do something and had no booth, first you got to get everything really clean. Car, work area and you. Second airflow is not your friend painting in the open. Yes you want to remove the overspray but real airflow will just kick up dust. I did one recently where I actually had less trash than in some booths. Just had some box fans (3) in the garage door openings. Pulled the garage door down, and used plastic to seal up around the fans and door. Barry has said something similar as well. He mentioned that he could spray something in the open shop and not have much issues with trash. If you can get your work area really clean, as well as your car, wear a paintsuit and spray sock, tack between every coat of sealer and base, then tack again before clear, you can get a reasonably clean job, provided you don't have a lot of fallout from your ceiling. Is it ideal? Of course not but sometimes you gotta do what you gotta do.
 
Big key for what I said above is if you do get trash in the sealer or base, to nib it out, and recoat (if nibbing base). Most trash that you get in clear you can sand out when color sanding. You just don't want to have big lumpy trash in the base or sealer because when you start color sanding you will sand through the clear and often the base too where the trash is. Why denibbing is important.
 
Chris_Hamilton said:
Big key for what I said above is if you do get trash in the sealer or base, to nib it out, and recoat (if nibbing base). Most trash that you get in clear you can sand out when color sanding. You just don't want to have big lumpy trash in the base or sealer because when you start color sanding you will sand through the clear and often the base too where the trash is. Why denibbing is important.
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Chris i was sure i had a fly in it.......but he flew away lol. if i get this done with no flys in it, its gonna snow a blizzard.
on the plus, it has been no trouble at all to maintain temps. of course its not really cold yet either.
 
Treeslayer said:
Chris i was sure i had a fly in it.......but he flew away lol. if i get this done with no flys in it, its gonna snow a blizzard.
on the plus, it has been no trouble at all to maintain temps. of course its not really cold yet either.
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Best time to not have insects is the morning. If you can, get everything in place beforehand, seal up any openings around your fans with plastic, and hang a couple of flypaper traps. That will pretty much eliminate any insect issues if you don't leave any door open etc.
 
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