Modeling in Living room - Airbrush question

Skyking66 wrote:

Hi All   I am currently modeling in my living room on a coffee table, I live in an appartment and this is the only available space.   I am thinking of getting an AB setup with an 11 Gal tank filled at the local gas station. I tried researching the forums but did not find the answer I was looking for. My question is, can I AB in the living room without creating much mess? How much of an overspray will I get ? I planned on Abing inside a cardboard box set on a cofee table. Am I crazy to even think abou this? Myself and my SO are not extremely sensitive to odors so this is not an issue, I can ventilate the space pretty easily too.   Thanks for the help,   SkyKing66

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Title Spray Booth Design And Fan Selection Date Added June 24, 2003

Author Klaus Raddatz Screen Name Dadsworkbench

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This is not intended to be the final word on spray booth design, fan selection, or a criticism of anyone's spray booth, but to share what I know about booth design and provide a guide to take some of the experimentation out of building your own spray booth. Also, please keep in mind that we're designing a hobby paint spray booth using some of the design principles of full sized booths. This should not be interpreted as a guide to building a full sized spray booth.

{A Plenum of 2" is nessesary to have a even draw of air from fan to front of Filter drawing the air through the filter for it to draw the air evenly...}"RC"

When it comes to fan selection, there are usually concerns about drawing too much air into the booth and contaminating your paint with dust/dirt. In determining the airflow through your booth keep in mind where your spray booth will be used, the type of spray equipment that you'll be using, and the ambient condition. While some compromises are possible, dusty environments should be addressed through means other than reduced airflow through the booth. The goal in building a spray booth is to create a healthier working environment by exhausting the paint fumes from your workshop.

Several things to consider before selecting a fan for your spray booth are spray booth size, direction of draft, airflow requirements, duct diameter and length, and static pressure.

SPRAY BOOTH

Booth size and proportion are dependent upon need. Make sure the booth will accommodate your largest part and you can comfortably paint within those confines. If you're not sure about proportions, build a mock-up out of cardboard first and try it. Then transfer those dimensions to whatever material you're going to use to build your booth. Something to keep in mind when you're deciding on size: the larger the booth, the larger the fan you will need to exhaust it, and fan prices go up with CFM and SP ratings. Also, consider adding a plenum chamber between the fans and the filters. 1:1 spray booths use plenums to even out the airflow across the filters.

DIRECTION OF DRAFT

Most 1:1 spray booths are totally enclosed and designed with either a cross-draft or a downdraft airflow. Cross-draft booths pull air across the booth from inlet filters typically located in the booth doors, into exhaust filters located directly opposite the inlet filters. Downdraft booths pull air downward from inlet filters located in the ceiling, into exhaust filters located in the floor.

From a hobby perspective, it's not feasible to build a totally enclosed spray booth. Hobby spray booths are typically small, open-faced bench top units, drawing in unfiltered air for ventilation, as shown below. As such, problems can occur with dust and dirt settling in the paint. This is especially true in cross-draft booths where all of the air entering the booth is drawn across the part being painted. Dust contamination is reduced somewhat in downdraft booths due to the lower air volumes required for ventilation and the air being pulled downward as it enters the booth. Adding an inlet filter to the top of the downdraft booth, can further reduce the amount of unfiltered air drawn across the part.

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As for venting to the top of the booth, it's normally not done that way because of the adverse affects it can have on finish quality. It's important to realize what happens when you vent to the top of the booth. First, you're working against gravity; that means you'll need higher airflow rates for proper ventilation. Secondly, the updraft pulls the atomized paint away from the part, requiring higher spraying pressures to compensate. The finish problems created by high airflow rates and high spraying pressures, are further compounded by the limited adjustments on airbrushes (versus conventional spray guns), and limited thinners and reducers available for hobby paints. Although automotive thinners and reducers have been used in hobby applications, their corrective properties may not be sufficient to overcome a poorly designed spray booth. Finally, when venting to the top of the booth, there is a good chance that overspray particles in the filter will fall down into the paint. It's not a good idea to hang dirt above the part you're painting.

My spray booth (shown below) is a cross-draft booth that measures 17 1/4" tall, 24" wide, and 19" deep. The top of the booth is set back about 9" to provide clearance for overhead spraying, and I've added a 2" plenum chamber to even out the airflow across the filter. Another advantage of the plenum is that if I find I've installed too large of a fan, I can vent the plenum chamber to allow the fan to draw in outside air, thus reducing the airflow through the booth. I've also added a door so I can close the booth after the fans are turned off to prevent dust from settling in the paint.

Click To Zoom

AIR FLOW REQUIREMENTS

Once the spray booth size and direction of draft are determined, calculations for fan requirements can begin, starting with air movement through the booth. For cross draft booths, this is known as face velocity and for downdraft booths, it's known as downward velocity. Industry standards specify that the air velocity through a cross draft booth should be 100 FPM, empty, meaning no operator or parts are present. For downdraft booths the specification is 100 FPM past the operator, meaning the operator and part are present when readings are taken. Some applications require more or less velocity depending on the type and quantity of material being sprayed, the applicator being used, and the direction of draft.

The rules of thumb -- design cross draft booths with 100 FPM face velocity, and downdraft booths with 50 FPM downward velocity. A lower velocity is used for downdraft booths, first, because of gravity's effect on overspray, and secondly, when a mass (part and operator) is added to the inside of the booth, the airflow velocity increases because the internal volume of the booth has decreased. It's like pushing the same volume of air through a smaller pipe.

My booth, with a face velocity of about 75 FPM, works well with most spray cans and air brushes, although a higher airflow velocity would be better.

CFM Calculations

To calculate the cubic feet per minute (CFM) of air required to produce the desired face velocity in a cross draft booth or the downward velocity in a downdraft booth, use the following formulas:

Cross-draft CFM = inside height x inside width x desired face velocity (depth is not a consideration)

Downdraft CFM = inside width x inside depth x desired downward velocity (height is not a consideration)

For example, the inside height and width of my cross draft booth is approximately 18" x 24". To calculate for industry standards, multiply the height and width by 100 FPM: 1.5' x 2' x 100 FPM = 300 CFM

To meet industry standards, I need a fan capable of moving 300 CFM of air.

For my booth, I chose a reduced flow rate of 75 FPM, so I'll need a fan capable of moving 225 CFM of air: 1.5' x 2' x 75 FPM = 225 CFM.

But don't buy a fan yet, read on…

DUCTWORK

Figure out your exhaust duct routing to determine the length of the straight sections and the number of 90 and 45-degree elbows you'll use for your system. Measure the length of the straight sections, and refer to the Elbow to Straight Duct Conversion table below, to convert the elbows to straight duct, and then add it all up.

For example, my booth uses 4' of 4" straight duct, one 4" 90-degree elbow, and two 4" 45-degree elbows, as shown below. The elbow to straight duct conversion for a 4" 90-degree elbow is 6', and a 4" 45-degree elbow is 3'. Add up the duct lengths, 4' + 6' + 3' + 3' = 16', and I find my booth uses the equivalent of 16' of straight duct.

Click To Zoom

Click To Zoom

STATIC PRESSURE

Next, determine the static pressure in the ductwork. Static pressure (SP) is the resistance to air movement in the ducts, and is important in choosing a fan. The fan you choose must be able to deliver the required CFM at the static pressure level inherent to your ductwork.

Refer to the Air Velocities and Static Pressure table below. The values shown are for 100' of straight, smooth, aluminum duct. Find the duct diameter you'll be using and the CFM closest to the face velocity as determined above. Note the SP value and proceed to Calculate the Static Pressure in the Ductwork. Static pressure values not given were determined to be too high for practical application.

Calculate the Static Pressure in the Ductwork

To calculate the static pressure of your ductwork, multiply 1/100 of your duct length by the static pressure value.

For example, to meet industry standards, I need to calculate the SP for 300 CFM airflow through 16' of 4" duct. Multiply 1/100 of the duct length (for my booth - 16' x 1/100 = 0.16) by the SP value for the duct diameter:
4" Duct x 300 CFM = 4.19" SP (static pressure value from table)
0.16 x 4.19 = 0.67" SP (static pressure in the ductwork)

To meet industry standards, I need a fan capable of delivering 300 CFM @ 0.67" SP. This SP value is a little bit on the high side, so I might be better off using a 5" duct to reduce the SP and simplify fan selection.

In my booth, I use a fan capable of delivering 225 CFM @ 0.39" SP:
4" Duct x 225 CFM = 2.45" SP
0.16 x 2.45 = 0.39" SP

Also, if you're using flexible duct multiply the SP values by 3. Flexible duct is very restrictive.

I didn't include losses through the filters because it varies with filter media, however, furnace filters have minimal pressure loss when they're clean.

So, how critical is the SP to fan selection? Here's an example from a catalog, to give you some idea of how much the air volume is reduced as the static pressure increases. The free air (0.0" SP) rating of this particular fan is 320 CFM. At 0.5" SP that dropped to 50 CFM. In my booth that would produce a face velocity of about 17 FPM. Quite a bit less than the 75 FPM I'm currently using, and a pretty safe bet that my workshop will smell like paint. Not all fans will drop this much air volume, but without doing these calculations you'll never know. Also, keep in mind that many fans are rated only in free air (0.0" SP). If SP values aren't given, be careful. Contact the manufacturer to see if SP ratings are available. Some manufacturers have this information posted on their web sites.

Motors/Fans/Lights

Now, what type of fan? Bathroom, kitchen, induction motor, inside the booth, outside the booth…? You normally won't find an electric motor in the air stream of a production type spray booth, unless it's an explosion proof motor. 1:1 booths use externally mounted explosion proof motors. An explosion proof motor is certified as such by one of several industry recognized certifying agencies. None of the previously mentioned fans are explosion proof. Kitchen and bathroom fans are probably the most critical because they typically have exposed stator windings. Paint solvents, unlike cooking oils and hair sprays, can deteriorate the varnish on these windings and cause the motor to short circuit. Exercise caution if you're using these types of fans.

Also, keep in mind that voltage and current levels inside a spray booth must be kept below non-sparking levels, unless the components are certified as explosion proof. Non-sparking voltage and current levels are, if I recall correctly, about 16 volts and 50 mA, way below the 120 volts and several amps that many small fans use. Ultimately, the best type of fan to use is one that keeps the motor out of the air stream.

There are booths available that use computer type axial fans. These have induction motors located in the air stream, and while they're not explosion proof, their design makes them a better choice than bathroom or kitchen fans. I've taken a few of these fans apart and found the stator windings embedded in epoxy. Since epoxy typically has a high resistance to solvents, I feel comfortable that the solvents won't migrate into the stator windings and deteriorate the insulation.

Another alternative would be a fan with an externally mounted motor, such as the Dayton shaded pole blowers, available at Grainger.com (see table below). These blowers have been used successfully in spray booths, but please remember, they are not explosion-proof.

To find complete specifications for these blowers, go to http://www.grainger.com and search for the blowers by stock number. Depending on the booth size and the airflow restriction of your ductwork, one of these blowers should work for you.

When it comes to lights, florescent are preferred. They run cooler, use less energy, and tend to be more color correct than incandescent lights. Lights should be mounted outside of the booth for the same reasons that apply to motors - voltage and current. Cut a hole in the booth, install a piece a plexi-glass, and mount the light over the top of that.

Last thing, if your booth is metal or plastic; make sure it has a proper electrical ground. I spent a number of years in robotic spray finishing, and I can tell you first hand that electricity, whether it's AC, DC, or static, doesn't mix well with paint, unless of course you're painting with electrostatics. But that's another story.

Please remember A Plenum of 2" is nessesary to have a even draw of air from fan to front of Filter drawing the air through the filter for it to draw the air evenly..."RC"

I'll be finishing my spray booth for this winter, all I have to do is order the darn blower and I'll be spraying in my kitchen which is open to the living room.

I got to tell you guys this, you might get a kick out of it...?

At my buddies body shop he has a small paint booth in the corner. It's about a 40" cube with a huge 30" or so fan on the back wall vented directly outside. When I spotted it I mentioned that I would love to have that for at home doing my models. He looked at me and said, "You think so? Put a pice of paper on the turntable and turn on that switch." WOW that was the biggest paper shredder I ever seen!

He uses it when he has to do things like helmets and he hates wearing a mask or respirator. Well he sure doesn't in front of that thing. And yes, he proved to me that the paint will actually get on the helmet, just don't ask me how. 

Ok, thanks.

I do use a dust mask as well when spraying any paint. And i know all about resprators, i've worn resprators for everything from paint(industrial), buring paint, buring metal, sand blasting and fine wood dust. I am just not fimilar with acrylic based sprays and was not sure if a dust mask and box fan + filter would cut it.

While painting with acrylic's use a Dust Mask Or you'll be choghing up different coloered Spit and Loogies from the plastic bits ..If your painting with enamal= You use a resperator; as the fumes will harm your lungs and do possably non reversable damage to your lungs!...Down the road your gona die! Dust masks are not for Enamals! Only acrylics and like said above: breathing in the acrylics is breathing in Plastic! Also keep Babys and Animals Away from Paint being Sprayed!... You think second hand smoke Hurts you? This stuff Will Kill You and youre Wife & Baby & Animals....Thank you for listening!!

                                                         "RC"

Well it is acrylic. Just use a mask.  I use a three-stage filter mask with all of my spraying, enamel or acrylic.

Jesse

I had a thought, just how bad is spraying Future with a AB if your doing it indores with a box fan + furnace filter?

I ditto the mask part even with acrylics. Dried acrylic paint is nothing more than a form of plastic, and I suspect that coating the inside of your lungs with dried bits of plastic is not recommended.

While shaded pole blowers are the best thing to use. The kitchen hood isn't that bad. I use one, but then I also use acrylics. I do know I was more concerned with what kind of light to use than the blower. I'm not so sure I would have used the same idea for enamels though, but I'm basically a coward!

styrene wrote:

"I have one question myself. How worried do i have to be with all these flamable paint vapors and electrical things close togeather?" Shaded pole blowers (also called squirrel cage fans) are the best for spraying paints with flammable/combustible solvents.  In these fans, the electric motor is separated from the air stream.  STAY AWAY from bathroom exhaust, kitchen range hood, and computer fans.

I dont Know i built my paint booth out of an old range hood and havent had ay issues what so ever and i spray eneamel's all the time. I was cheap "free" so i couldnt comlaine. As for  over spray  youll get it on just about everything it floats in the air just like dust so be careful.

steveh wrote:

If you are not already using acrylic paints, now would be a good time to start doing so. They aren't completely non-toxic, but they sure are a whole lot less annoying in odor (and accident/overspray cleanup). Steve

Ditto that for me. I've switched to acrylics, and I'm glad I did.

Might also consider wearing a mask, just to be safe.

"I have one question myself. How worried do i have to be with all these flamable paint vapors and electrical things close togeather?"

Shaded pole blowers (also called squirrel cage fans) are the best for spraying paints with flammable/combustible solvents.  In these fans, the electric motor is separated from the air stream.  STAY AWAY from bathroom exhaust, kitchen range hood, and computer fans. 

To answer your question, the small quantities of paints and solvents used in airbrushing are typically not as hazardous as using a rattle can to do the same thing.  That's assuming, however, that you're spraying small scale kits.  Obviously, larger scale kits require larger amounts of paint, and appropriate precautions should be taken.  Spraying acrylics instead of lacquers or enamels is one way to reduce hazard potential; however, acrylics that use alcohols can also be somewhat hazardous, since methyl, ethyl and isopropyl alcohols are flammable.  Bottom line?  The more airflow/ventilation you can manage, the more vapor concentrations are diluted, and the more flammability hazards are reduced/removed.

Hope this helps some.

Gip Winecoff

I also plan on using an AB in an appartment (once i move) and have checked into home made spray booths, i have come accross 2 good plans.

#1 You know the fan/filter/light set ontop of some stoves? Well buy that by itself, get the proper type of filter (there is another one besides furnace filters, but i forget), cheap thin plywood to make a box fitting it leaving the front open, a light switch, dryer machine duct (keep as stright as possible to increase air flow) long enough to reach your window with either thin plywood or firm cardboard attached to the end that you can fit int0 your window. For added suckion add plexyglass (or glass) to the front leaving enough room for you to work with your hands under it, this will let less fumes escape.

#2 what i mentioned above, but replace the oven top fan set with a fan by itself. I have to look into the type more, but i'm thinking oven/bathroom fan. Someone on another model website built this setup for $60 us (without plexy glass i think). If you plan on building this, i proably can get a detailed account on just what he did for you.


I have one question myself. How worried do i have to be with all these flamable paint vapors and electrical things close togeather?

Here's a handy trick to check air circulation.

Once you get your fans or whatever you are using set up, light a stick of incense.  Wait a little bit and then walk around your apartment.  If you can smell incense in other parts of the apartment, you will definitely be able to smell paint fumes.

A guy at the local store told me to try priming with a rattle can in the bathroom with the fan running.  Let me tell you waht a disater that was.  After wiping the fine primer dust off every horizontal surface in the bathroom, I started shopping for a spray booth.  Some of the nicer ones have one (or more) carbon filters so you don't even necessarily need to vent to the outside if you are spraying acrylics.  

Here's a simple solution that might work for you.  Get a box fan (the kind that is about 20 inches by 20 inches)and put it in a window blowing out.  Get a furnance filter and tape it over the back part of the fan.  Airbrush in front of this setup.  The fan will push the air from inside of the apartment to the outside.  The furnance filter will help catch the overspray.  Try different speed settings to see which works best.

Jesse

If you are not already using acrylic paints, now would be a good time to start doing so. They aren't completely non-toxic, but they sure are a whole lot less annoying in odor (and accident/overspray cleanup).

Steve

Thanks for all the replies above, I guess I will try ABing without a box as sugested, newspapers are an obvious. Was thinking of using a fan, good sugestion. I was thinking of getting gravity fed, so my understanding is that it uses small quantity color cups anyway, right?

 

Now all I need is to decide which AB

SK66

The odor can be a problem, but overspray should be minimal. Your AB should be quite close to your subject, unlike the 12 inches recommended on a rattle can. The backdrop where I use the AB has virtually no paint on it.

The "mess" will be determined by the degree of preparation and organization prior to painting.  Put down plenty of newspapers, etc. to catch overspray. If not, your SO may not be your SO for very long!  Use the minimum amount of paint/solvent necessary to do the job (Try using a color cup instead of that 1 or 2 oz. paint jar.)

And get a fan or two going.  A small room fan placed behind you and slightly to the side will move vapors away from your breathing zone.  And don't put it on "high"; heavy crossdrafting can cause your paint to do things you don't want.  The idea is to a) dilute vapor concentrations and b) keep you from inhaling them.

Stay away from spraying in a cardboard box.  All that will do is concentrate the vapors and shove them back in your face.  Not something you want to happen.

Oh, yeah: open a window or two.  A supply of fresh air is always helpful.

Gip Winecoff

I tried that- once.

The amount of stuff that just floats off in the air is quite a bit. And the odor is quite strong if you use enamels.

I've started doing my airbrushing on our back porch. It's a bit of a pain to drag everything out there, but I don't have any space inside to do it. We should be moving into a new house early next year, and I'll have my own modeling room, with an outlet vent for a spray booth.

If you have the money, you might want to look into a spray booth that can vent the air outside. I've seen some folks make their own, too. Or you can go low tech and do it outside.

But I think if you try to do it inside without good ventilation- something that can move good volumes of air- it'll be unhealthy and smelly. All those fumes- enamel or acrylic- can have harmful effects if not vented well.