Auto Body Shops Pollution Prevention Guide
#5 - Paint Preparation and Application
Paint application wastes are generally comprised of leftover paints, incorrectly formulated paints, expired paints, air emissions of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs), and paint-contaminated wastes. The goals of pollution prevention in paint applications are to:
- Manage auto body repair materials properly
- Select less hazardous materials
- Improve paint application practices
- Reduce paint-contaminated wastes
Volatile Organic Compounds (VOCs)
- Include most organic solvents used in surface coating operations
- Examples includ toluene, xylene, and methyl ethyl ketone (MEK)
- Can lead to the creation of unwanted ozone smog in the lower atmosphere
- Can cause severe health problems
Hazardous Air Pollutants (HAPs)
- Include 189 materials listed in the Clean Air Act Amendments of 1990
- Examples include toluene, xylene, and methyl ethyl ketone (MEK)
- Include many solvents used in surface coating operations.
By keeping your work areas clean and free of filler and sanding dusts, you can prevent pollution and reduce the amount of time spent cleaning up and redoing dirty paint jobs. This can be accomplished by:
- Mixing and using body filler according to the containers directions.
- Wearing respiratory protection when sanding polyester or fiberglass filler -- these fillers have been determine to be a respiratory irritant and potential health hazard.
- Avoiding metal surface cleaning solvents especially those based on methyl ethyl ketone and chlorinated compounds (check Material Safety Data Sheet).
- Installing a central vacuum system to catch dust during sanding operations.
- Using a broom or vacuum to clean up body repair waste instead of water.
|Pollution Prevention In Action|
|Humes Collision Center, Inc. of Minnesota installed a vacuum sanding system for $9,000. The new contained sanding system has improved indoor air quality, reduced employee labor costs for cleaning dust off cars and in the shop, and almost eliminated the need to redo work on cars damaged from dust participles. In addition, air filters are changed less frequently and the amount of sandpaper used has been reduced. Since installation, Humes has saved over $7,000 a year, primarily from labor costs (Auto body Repair Shop Waste Reduction Measures, 1993).|
The surface coating process can produce two types of waste that auto body shops should be concerned about: hazardous air emissions and hazardous waste. To help reduce the emission of VOCs and HAPs, finish material manufacturers have agreed to produce more low VOC-containing materials. Examples of low VOC-containing surface coating materials include water-based or high-solid application materials. In water-based paints, water has replaced most of the VOC-containing solvent to help the paint flow smoothly and evenly over the applied surface. The advantages of using water-based paints include:
- Reduced VOC emissions
- Reduced personnel safety hazards
- The elimination of potentially toxic solvents
The disadvantages of using water-based paints include:
- Availability may be limited
- Corrosion resistant spray painting equipment may be necessary
- Water-based paints may take longer to dry
- May be difficult for technicians to apply
High-solids paints have more solids and less solvents and can reduce VOC emissions by up to 75%. The main disadvantage of using this type of paint is the increase in paint viscosity or thickness. You may also want to consider using powder coatings. Powder coatings are 100% solids; therefore they do not contain any VOC-containing solvents. The part to be painted is reheated and/or the powder particles electrostatically charged to enable the powder to cling to the part's surface. The part must then be baked to help the paint cure. Unfortunately, the cost of using such coatings can be prohibitive. The advantages of using powder coatings include:
- Overspray can be collected and reused
- Reduced VOC emissions
Determining VOC Content
To calculate the VOC content of a particular product, look first in the Material Safety Data Sheet (MSDS). The MSDS usually lists the VOC content of the product as shipped in pounds per gallon (lbs/gal), minus water and non-VOC-containing solvents. Note that this may not be the actual VOC content of the product in application form. Most products require additional reducers, thinners, or hardeners for proper application. These additives can contain up to 100% VOCs by volume and could alter the VOC content of the coating. See the following example of calculating VOC content.
VOC Content Calculation Example
Your job is to apply a topcoat on a vehicle. To get the proper coating, the topcoat has to be mixed with a hardener and a reducer at a ratio of 2:1:1. The VOC content in the paint alone is 4.50 lbs/gal. To determine the overall VOC content of the material to be applied, you have to consider all the potential sources of VOCs
The applicable product would have a VOC content of 5.75 lbs/gal, not 4.5 as listed on the MSDS. (Source: Auto Body Surface Coating: A Practical Guide to Reducing Air Emissions, 1994.)
When comparing product VOC content, you also have to consider the total amount of the product to be applied. If a product has a low VOC content but requires four or five applications, it may actually release a greater volume of VOCs during the application than a high VOC product that will perform equally well using just two light coats.
Sources of VOC Emissions in Paint Application
Topcoat applications release approximately 55% of the VOCs emitted during the refinishing process. The high release of VOCs in this step is attributed to the poor transfer efficiency of traditional spray equipment. Over half of the topcoat material can be lost as overspray.
Equipment cleaning contributes approximately 20% of the VOCs released during the refinishing process, while undercoat applications are responsible for approximately 17%, and surface preparation materials 8%. (Source: Auto Body Surface Coating: A Practical Guide to Reducing Air Emissions, 1994).
Improper paint application techniques not only waste paint but your money as well. A measure of how much paint actually coats a surface compared to how much is applied is call transfer efficiency. By increasing your paint transfer efficiency you can:
- Purchase and use less paint
- Replace paint booth filters less frequently
- Clean the paint booth more easily and less frequently
- Reduce VOC and HAP emissions
To increase your paint transfer efficiency:
- Use efficient application equipment
- Provide training for your paint booth operators
Efficient Application Equipment
The standard air spray gun transfer efficiency rate can range between 20% and 50%. However, to minimize waste, you should strive for 65% or greater transfer efficiency rates. This can be accomplished by using the proper equipment in the hands of a trained sprayer.
Some high-volume/low-pressure (HVLP) spray guns achieve transfer efficiencies of up to 90%, making them one of the more efficient spray guns on the market today. HVLP spray guns use compressed air (at about 20 cfm) to atomize the paint under lower pressure (10 psi or less). This system provides a higher air flow rate than conventional paint guns. The disadvantages of using HVLP equipment over conventional equipment include a potentially higher price tag and slower application rate.
Low-volume/low-pressure (LVLP) spray guns also use compressed air (at about 7 cfm) to atomize the paint under low pressure (10 psi) and with a lower air flow rate. An advantage of using LVLP systems is that you can have a transfer efficiency ranging between 55% and 75%. A disadvantage of using LVLP spray guns is that many have a pressurized cup which is only pressurized when the gun trigger is pulled. This could cause a delay in material delivery that may affect an applicator's technique. When choosing a spray gun, consider the following:
- Determine the price range you are willing to spend for spray equipment
- Determine the types of coatings you will be using
- Select spray equipment that will achieve the highest transfer efficiency based on your needs and price range
A high transfer efficiency spray gun is not very effective if it is used by a poorly trained operator. If you would like more information on paint application training opportunities, contact:
- The Iowa Waste Reduction Center (800) 422-3109, (319) 273-8905, and inquire about STAR Training nationally.
- Your local or state pollution prevention program.
- Your paint supplier
- Your local automotive trade association
Follow these suggestions for improving your spray technique:
- Always hold spray gun perpendicular to the surface being sprayed, using parallel strokes. Never arc the gun.
- Hold gun six to eight inches away from the surface to be sprayed.
- Use a 50% overlap for each pass, feathering the gun's trigger at the beginning and end of each stroke. This technique may not work with all types of paints such as high metallic, high solids basecoats.
- Use a comfortable speed for each stoke, especially with larger panels.
- Spray the border edges of the piece to be painted first to assure all edges are covered without extending the spray pattern beyond the borders of the piece.
- Make each pass the full length of the panel when spraying small and medium sized panels (Auto Body Surface Coating: A Practical Guide to Reducing Air Emissions, 1994).
Paint-contaminated wastes include shop towels, masking paper, and mixing cups. To prevent these wastes from becoming hazardous waste, avoid using paints that contain heavy metals (such as lead and chromium) and potentially hazardous solvents (such as chlorinated solvents). To reduce the amount of non-hazardous and hazardous paint-contaminated wastes produced in your shop:
- Use reusable (launderable) cloth towels if feasible.
- Instead of using paper masking material, switch to a liquid mask that can be washed off with water
- Use reusable mixing cups and sticks, washing them in an automatic gun washer.
- Remix paint for undercoats and base coats if feasible.
- Give leftover paint to customer for touch-ups.
- Keep track of your inventory so that paint and thinners do not exceed their expiration date.
Special Note: Hazardous air emissions from the paint application process can also be controlled by installing air filters in your spray booths and a tall ventilation stack. Stacks help to disperse escaped particles over a wider area, instead of concentrating them around your shop. For more information, contact your state Small Business Ombudsman.
|Pollution Prevention In Action|
Collision Pro Auto Body Repair of Montana switched to HVLP spray guns in their paint booths. With the HVLP spray guns, the technicians use about 35% to 50% less paint. Collision Pro also mixes base coats and primers in small batches to control usage and prevent waste.
Humes Collision Center, Inc. of Minnesota replaced their old microfiche system for mixing paint with a $7,000 computerized system. Humes uses less paint with the new system, reducing the average paint cost for each car from about $36 to $16, and reduced the amount of paint waste produced. Based on painting 10 cars per week, the shop is saving about $10,000 a year on reduced paint purchase costs.
Humes also switched from plastic car bags to a masking liquid. This liquid can be applied with the same spraying equipment used for painting cars. The liquid is removed with water (no detergents needed) and then disposed of with the shop's wastewater. Humes has saved almost $2,000 a year in reduced plastic bag purchasing costs and reduced the amount of solid waste generated (Auto body Repair Shop Waste Reduction Measures, 1993).
Clean Air Act Amendments
To help protect our air, the U.S. Environmental Protection Agency (EPA) passed the Clean Air Act Amendments of 1990 (CAAA). These amendments strengthen existing federal and state controls on major sources of air pollution. They also contain new requirements for smaller sources of air pollution, which are most often small businesses. The CAAA requirements include measures to:
These questions can help you develop ways of preventing pollution in your shop.
|Paint Preparation And Application||YES||NO|
|1) Do you use good housekeeping practices? Instituting simple housekeeping practices (such as mixing only as much paint as you need, using easy-to-clean paint cups, and keeping lids closed) will help reduce wastes, HAP and VOC emissions, and increase worker safety.|
|2) Do you check the MSDS for a product prior to purchasing it? It is important to check the MSDS in order to avoid chemicals that contain hazardous materials, chlorinated compounds, or contain VOCs or HAPs.|
|3) Do you use a broom or vacuum to cleanup around sanding jobs? Use a broom or vacuum with proper dust-collecting filters instead of using water and solvents to clean to help prevent wastewater from becoming contaminated (and possibly hazardous). Before disposing of sand and dust, determine whether the waste is hazardous.|
|4) Is a respirator worn when sanding? To protect your respiratory system when sanding, use either an air purifying or air supplying respirator.|
|5) Do you use a vacuum sanding system? To contain all sanding and paint debris, use a vacuum sanding system. This could greatly improve indoor air quality and extend the life of your sandpaper.|
|6) Do you do any wet sanding? When wet sanding, allow the wastes to dry, then sweep them up and dispose of them. Prior to disposal, you must determine whether the waste is hazardous.|
|7) Do you buy products in aerosol containers? If possible, avoid purchasing any material in aerosol spray cans. This type of delivery system is very wasteful compared to other methods.|
|8) Do you use solvent stripping in your shop? To help reduce waste disposal costs, use more efficient paint stripping methods, such as media blasting with glass beads or carbon dioxide pellets. Depending on what you use, the only waste produced may be the paint itself.|
|9) Do you require your operators to be trained in paint application techniques? Transfer efficiency is also a function of operator skill and training. Operators should be trained on how to apply paint most efficiently, for example, by not arcing the spray gun and not blowing paint into the air.|
|10) Are you concerned about the application efficiency of your paint guns? Overspraying can waste your paint as well as ruin paint booth filters. Select the most efficient spray gun system you can afford that does what you want it to do.|
|11) Do you mix up just enough paint to complete a job? Varying paint cup sizes could be an effective means of source reduction by limiting over-mixing of paint and decreasing the amount of solvent needed for equipment cleanup.|
|12) Do you remix leftover paint for use as a base coat or undercoat? Instead of having to dispose of leftover paint, use it as a base coat or undercoat, or give to the car owner for touch ups.|