Wood Finishing Technique: Some Thoughts On Safe Locations For Spray Finishing

By Bruce W. Maki, Editor

Start:

There are many places I have done spray painting and wood finishing: Outdoors, garage, basement, and professional spray booths. I believe spray finishing can be done safely in each environment, providing sensible precautions are followed.

Spray Finishing Outdoors:

Perhaps the most logical place to do spray finishing is outdoors. The benefits are obvious... lots of space, more-than-adequate ventilation, and little or no risk of explosion. But spray finishing outdoors has some potential problems:

Temperature Control: Most paints, stains and urethane products have a narrow temperature range that is suitable for their application. Here in Northern Michigan I could spray outdoors almost any day in the summer months, but that leaves about two-thirds of the year where it's too cold. In warmer climates it might be possible to do spray finishing during the cooler times of the day, perhaps early morning or late evening. Spraying in direct sunlight might not be the best idea because when coatings dry too fast many problems can arise.

Rain: What more do I need to say?

Bugs, Dust and Other Junk: Bugs like to take a break from flying, and they are certain to discover your project. Maybe oil-based paint, stain or urethane smells like food to certain bugs. If it's warm and sunny enough, flies might not land on your work because they will need to stay cool in the shade.

There's not much anybody can do to control the dust or pollen that falls in their backyard, but after it rains there is usually less dust in the air. However, after it rains there is often a chance of... more rain. I'll look at the National Weather Service's website to check the radar for my area.

If there are trees around, it seems that there's always something falling... leaves, twigs, bits of bark, bird poop, squirrel fur, etc. You can't win. I guess it's a good idea to stay away from tall trees.

Overspray: Preventing overspray is impossible, but it can be monitored and there are ways to control it. Distance is your friend. I wouldn't spray outdoors unless I had lots of open land and great distances between my spray gun and anything owned by someone else. How much distance? I don't know. That's the problem... overspray might travel hundreds of feet before it dries into a dust-like powder. It depends on how fast the droplets dry, which is hard to predict.

I will only spray outdoors if the wind is very light and if the direction of wind blows the overspray away from anything valuable, such as the neighbor's house or (most important) cars. I frequently stop spraying and look around for evidence of overspray getting on nearby objects, and faraway objects too. I have often been surprised by the distance overspray can travel.

A few years ago I repainted the cab of my truck. I disassembled the body panels and painted them outdoors on sawhorses or laying across my small utility trailer. You can read about this repainting job on yet another website that I publish.

In my article about installing an extension to a privacy fence, I spray painted sections of lattice with a Wagner power sprayer. The Wagner power sprayer makes A LOT of overspray, so it's important to keep some distance from anything that could be damaged by overspray.

In the above two pictures I was working in the back yard of a rural house I lived in several years ago. That house had five acres of land and there was lots of open farmland on three sides of the property. The nearest house was at least 300 feet away. I had no problems with overspray getting on anything valuable.

Spray Finishing In The Garage:

A garage would be the next obvious choice for spray finishing locations. It's out of the sun, the rain, and birds rarely fly over your project. In cold weather a garage may not be a suitable location for spraying, unless it's insulated and heated.

If adequate cross-ventilation can be achieved, a garage could be a safe place to spray paint, stain or urethane. What exactly is "adequate ventilation"? I don't know. Some characteristics of adequate ventilation: There are no explosions, and nobody gets sick, light-headed or dizzy from the fumes. And nobody develops cancer or brain damage later in life.

There are only a couple of times that I've done any spray finishing in my garage. When I did, I opened the garage door about 12 to 24 inches, I opened at least one additional door or window, and I put large box fans in places that would create a good cross-flow of air.

Since the vapors from most common solvents are heavier than air, they will sink. It makes sense to place fans at floor level, blowing air into the garage at one side and blowing air out the opposite side. It doesn't make sense to fight the prevailing wind direction... it's better to place the incoming fan on the windward side of the building (the side exposed to the wind) and the outgoing fan on the opposite side.

I suppose a fully-opened garage door would do the best job of preventing vapors from building up, if there is another door or window open and a fan running. But... when the door is opened completely there may be a greater chance of overspray getting outside and onto something valuable. (Isn't this a pain-in-the-a$$?)

Spray Finishing In The Basement:

Most of my spray finishing has been done indoors, in a basement. While it hasn't happened to me yet, THERE IS ALWAYS A CHANCE OF BLOWING UP THE HOUSE. Seriously.

When I've done spray finishing in a basement, I ALWAYS do the spraying directly in front of an open window with one of more large fans blowing the air OUT. I also place another fan in a window on the OPPOSITE side of the building, blowing air IN.

I only use fluorescent lighting around my spray area. I don't use halogen work lights because they get so hot I fear they might ignite the vapors. I've heard about fires where that happened. Even regular incandescent lights might be capable of igniting the vapors.

In this photo you can see the fans in the open window behind me. Those are 20 inch box fans, which I bought at Home Depot for about 15 bucks. The grills and blades on these fans developed a coating of stain and urethane, which tells me that they are doing their job.

Also, note the plastic sheets beside me. I rigged up 2 of these by cutting a sheet of polyethylene plastic, rolling a 1x2 around each end and stapling it. The upper board is screwed to a beam above. When done spraying I just roll up the plastic around the lower board and hold it up with Velcro straps. These sheets do a great job of keeping overspray away from the rest of the basement.

Where Do The Solvent Vapors Go?

While writing this article, I looked online for information about the vapor density of various solvents. I was under the impression that most of these vapors were lighter than air and therefore would rise upwards. I was wrong. Just because you can smell the vapors doesn't mean they are all rising up. It turns out all of the common household petroleum solvents emit vapors that are heavier than air.

In the above photo, it's entirely possible that flammable vapors were gathering on the floor behind me. Luckily, I had another fan just behind the camera, blowing air across the floor towards the window. This probably stirred up the air enough to prevent a dangerous ponding of vapors.

BUT... five feet behind the camera sits my gas water heater, which has a standing pilot light. A pilot light is a common cause of flammable vapor fires. If the vapors had been able to flow back along the floor, I could've had a big problem.

The next time I do any spray finishing in my basement, I will take a small tilting fan and place it on the floor near the wall, blowing air upwards toward the window. That should keep fumes from building up near the floor. The goal is to bring fresh air in a basement window, blow air across the floor towards the spray area, then blow air up towards the out-blowing window where my two large fans will suck the air and vapors outside.

Just to be on the safe side, it would be a good idea to turn off the gas water heater, so the pilot light goes out. Of course, that means the pilot needs to be re-lit later, and there might not be enough hot water for anybody else in the house.

Overspray Problems: Since the fan blades get coated with stain and urethane, I knew that overspray was getting outside. My neighbor's house is about 12 feet away from that open window. Realizing that there was a chance that some overspray could reach their house, I rigged up a simple deflector to make the air turn upwards. I just placed a wheelbarrow on it's side about 3 feet from the fans, so the air and overspray were deflected upwards or back towards my own house. I didn't see any traces of overspray on anyone's siding.

Spray Finishing In An Industrial Spray Booth:

Industrial paint booths are designed for spray finishing. Most have built-in furnaces to heat the air in cold weather, and some have air conditioning to keep the air cool in hot weather. All are designed to minimize or eliminate the risk of fire or explosion.

While I'm not going to suggest that you spend tens of thousands of dollars on a professional-grade paint spray booth, it might be possible to borrow or rent one.

You might find a custom-cabinet company in your area that has a spray booth. Maybe they aren't using their booth 100% of the time, and maybe they would be open to the idea of letting somebody else use that booth for an hour a day over a couple of days. The bigger problem is: Where do you park your project while it dries, and where do you do the scuff-sanding that is required between coats of urethane? If they have a small section of their shop that you can borrow/rent to scuff the finish before applying the second coat then this idea should be workable.

If you were going to try this approach, it would be best to provide your own spray gun (make sure their air hoses can connect to your spray gun, or get some fittings that will work), bring your own stain, urethane, and solvent for cleaning up, and bring your own organic vapor respirator.

If you stayed out of the way of their workers, didn't interfere with the flow of their projects, and worked around their schedule, this might be a feasible solution for somebody looking to spray finish their own furniture or wood trim.

A more likely place to do spray finishing is a local independent auto body shop. I'm referring to body shops that are not part of a large chain, and are not associated with a new car dealership. I've learned that some smaller independent auto body shops find it increasingly difficult to make a decent profit doing repair work that is paid by insurance companies. Consequently these shops sometimes prefer to do custom work, car restoration, and special non-automotive painting/finishing jobs.

I suppose a do-it-yourselfer could call some of the smaller auto-body shops in their area and (if they have a spray booth) ask if they would be willing to rent out their spray booth and a small area of their shop. I've seen it done before, but please understand that not every body shop would be willing to do this. If you are looking for a safe place to apply spray finish, it might be worth a phone call.

The same suggestions mentioned earlier still apply: Bring your own tools and materials, and don't make their life difficult.

In this photo, the painter is spraying a car hood. Note the vent inlets down low on the wall. This spray booth is big enough to fit a large car, pickup, or SUV, so it's big enough for any furniture or amount of trim. This photo was taken for an article on BodyShopZone.com, which I publish with a friend who is an experienced auto body technician.

A properly equipped industrial paint booth is the only location that I would actually recommend to anybody wanting to try spray finishing.

While I've done spray finishing outdoors, in my garage and in my basement, I'm not going to recommend those locations to anybody. If you chose those locations, that is your decision, and you bear the consequences.

Copyright © 2009  HammerZone.com

Written January 15, 2009