Best practices in the mixing room

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In painting, there are numerous variables that painters can’t control. To compensate, they must pay strict attention to the areas they can control, such as the painting room. There are many variables that must be controlled, but are often overlooked. Painters spend so much time engrained in the routine of working in the mixing room — mixing formulas, cleaning equipment and recycling solvent — that things they know should be checked or maintained are sometimes pushed aside in order to get the job finished. Too often, the paint job suffers as a result. Some of the more difficult-to-correct and costly mistakes, such as a corrupt bank, can happen when even slight errors are made, and the consequences may not be apparent until long after.

As with many items in the collision repair industry, if a plan is made and a standard operating procedure (SOP) is developed to routinely check the mixing room and all its variables, consistent formulas and color match can be maintained. Paint shop SOPs are critical. Paint shop margins are very lean, so maintaining a strong profit margin takes work. Processes must be effective and take up as little production time as possible. As with a routine for changing oil, it is often “Pay now, or pay more later.”

Regulatory requirements
Depending on your shop’s location, paint mixing rooms may have mandated requirements, and you should check state and local requirements to comply with your area. The Environmental Protection Agency (EPA) publishes a document for best practices in the mixing room (Fig 1) with topics including storage guidelines, personal protection equipment suggestions, ventilation requirements and equipment maintenance.

The EPA warns against open containers. All containers must be sealed when not in use. Not only do open containers waste money, but they also allow Volatile Organic Compounds (VOCs) to vent to the atmosphere. Even waterborne paint has co-solvents — agreeably much less — but it too contains solvents.

Whether your shop mixing room is a manufactured one attached to the booth or not, its ventilation should be maintained. The filters, both intake and exhaust, should be checked and changed regularly. Solvent vapors are generally heavier than air, so they will lie at the bottom of the mixing room. The ventilation should be drawn off from the floor and brought in from the top or at the upper end of the wall.

Paint vapors are generated in the mixing room; and though we may not notice them as much as in the booth, an air-purifying respirator with an organic vapor cartridge should be worn at all times (Fig 2).

Keep the mixing room free of dirt, spills and clutter. Dirt in the room will find its way into the mixed paint, so to avoid that, the room should be cleaned on a regular basis (Fig 3). The toner mixing rack should be maintained as well. The machine and all other potential spark-producing objects should be bonded with ground straps. Even static charges from plastic containers could be catastrophic. Empty containers should be disposed of as they accumulate, as mixing rooms can quickly become cluttered, leading to potential mishaps. Spills should be cleaned up, according to local requirements, immediately.

As toners or other supplies are used, a tracking system for restocking should be established. Toners should be kept in a logical order on the mixing machine, and as soon as they are used, the spout should be cleaned and placed back on the mixing bank. If all the toners for a formula are taken off the mixing bank, or if a toner is not replaced as it is used, grabbing the incorrect one is more likely. Paint materials are costly, and if a partly mixed formula must be discarded, it severely impacts profits. Toner lid fit should be checked regularly, as should the mixing bank for proper operation.

Scales should be kept clean (Fig 4), level and calibrated at all times. Some scales have leveling feet that can be adjusted. If the scale does not have a level on it, it should be adjusted with a small torpedo level, both with pan off and on, to ensure the pan supports are not holding it at level. Some scales will indicate a fault code such as “L” when the scale is not level.

The pan and paint table should be kept clean. Though a scale will zero out the weight of a spill, if the paint is not in the can, it is not in the mix. The scale should be calibrated according to the manufacturer’s recommendations, and if you do not have tools or knowledge to do so, your jobber can likely do it for you. If the scales pan has dried paint on it, it could be either out of level or calibration. The accuracy of a scale, especially when mixing small amounts of paint, is critical to the color match.

Personal protection equipment
Wear chemical-resistant gloves, clothing and eye protection. Skin and eyes are vulnerable to absorption of toxic chemicals present in many products in the mixing room. Many of these chemicals, which may be an irritant to the skin and eyes, also can be absorbed into the body and cause damage to internal organs.

Remember that nitrile or butyl rubber (Fig 5) will protect you; latex does not. Eye protection should consist of either a full-face protector over safety glasses (Fig 6) or goggles. Splashes can get past safety glasses alone.

Handling waste
Practicing waste reduction in the shop not only helps the environment, but also reduces business material and waste disposal costs.

By mixing only the amount needed for a job and using an HVLP spray gun, which has higher transfer efficiency, you will cut down on materials used. Most paint companies offer a calculation program on their computerized systems so the correct amount for the job can be mixed. If your shop doesn’t have this program, most paint companies can tell you the average amount of ounces needed to paint a panel. The painter can then do the math and not mix up excess amounts of materials.

Automated gun cleaner
Gun cleaning machines save both the environment and money. Designed to reuse cleaning solvents, they have covers to prevent evaporation and provide a clean gun with less hands-on work, allowing the painter to multitask.  Guns should be pre-rinsed before they are put into the machine.

Solvent recyclers
Though not mentioned in the EPA publication, a solvent recycler will take old solvent and remove the majority of the non-solvents in the material, leaving two products: reusable cleaning solvent and 'still bottoms" to dispose of, which is significantly less the what was put into the machine.

Mixing
The mixing of a formula should be done with care. Each manufacturer has recommendations for how and when their paint should be agitated.  However, there are some coatings that should not be overmixed. Some brands of waterborne paint only require a slight rocking of the container before pouring into a formula, for example. Each painter should know and follow the recommendations of the manufacturer for their shop’s specific product.

Toner bank
As stated earlier, the toners should all be turning when being agitated. Some mixing machines have a yellow plastic piece that bounces as the paddle turns in the toner can, making it easy to see when it is not turning; others must be checked more closely. Dented cans or incorrectly fitting lids may also keep the toner paddle from mixing. Most mixing banks have room behind the toner that is used to store spares of a color. Those spare cans should be stored upside down to minimize pigment settling; when a can stored in this manner is turned upright and the agitating lid attached, it is easier to suspend the components than if they remained stuck to the bottom.

Shelf life
Though shelf is not an issue with most solvent-borne paints, which can last for years if they are kept from drying out, waterborne toners will go bad if not used in time. Painters should check with their jobber or manufacturer for their brand’s time recommendation.

Corrupt bank
A corrupt bank occurs when a toner is poured off without being agitated, or before it is in correct suspension. A toner poured off in this corrupt state will cause a formula mix that does not match. But more importantly, the colors mixed with that corrupt toner are likely to not match either. This mishap can occur without being noticed, and the painter may look for other possibilities before discovering that the bank has one or more corrupt toners. Even if a painter suspects a corrupt bank, finding the culprit toner is difficult. The painter must correlate the common toners to the mismatch formulas in order to replace them. This is a difficult and tedious process that can be avoided by proper agitation. Some paint manufacturers recommend that new toners be placed in a shaker for as long as 30 minutes before attaching an agitation lid and placing it on the mixing bank.

Pouring the toner
Though there are computerized (Fig 7) pouring machines for precisely mixing formulas, most of us still do it manually. Formulas, especially small ones, must be mixed precisely. Every number must hit correctly. Even if the computer will re-calculate the pour, there may not be enough room in the container, and if the correct amount of paint was calculated, the recalculation will overmix the amount needed.

The toner should be held so the pour hits the center of the container (Fig 8), and the can should not be rocked back and forth to control the amount of paint that comes out. It should be held so the paint will freely flow out when the gate is opened with the thumb or finger (Fig 9). The pour can start at a fast rate and be slowed down by partially closing the gate as the amount reaches the correct weight. Some scales may need to catch up with a fast pour, so be careful as you near the desired amount.  Pour precisely. If you believe that + or –1 is OK, you may get away with it sometimes; but the times you don’t will be costly.

Labeling
If the paint is mixed just before it is used and the precise amount calculated and used, there may not be a need for labeling. But if it is mixed on one day and used on another, the container must be labeled. If there is more than one painter or if painters’ helpers edge in some parts with paint, waiting for the job to be completed, the mixed paint must be labeled. Silver is a common color, for example, and though silvers may each appear to be quite different on the vehicles, they may be hard to distinguish as liquids. Labeling is not only required by law, but it is a wise practice.

EPA 6H RULE
A federal Environmental Protection Agency (EPA) regulation has mandated that all facility painters follow the EPA Rule 40 CFR Part 63 Subpart HHHHHH (EPA 6H Rule). On Jan. 9, 2008, the EPA accepted a new standard known as the HAPS 6H Rule to reduce the public’s health exposure to hazardous air pollutants (HAPs). The agency’s main objective is to significantly lessen the amount of HAPs released into the environment during paint stripping or surface coating operations. During such work practices, the most dangerous chemicals, namely, methylene chloride (MECL), cadmium, chromium, lead, manganese and nickel compounds, represent significant risk to employee health if proper engineering and administrative controls are not in place.

Because the requirements are extensive, the EPA is allowing existing facilities until Jan. 9, 2011 to reach compliance. Body shops should review EPA’s 6H checklist to ensure that their paint spray operations are compliant with the EPA 6H rule. Here are some helpful links or contact your paint supplier:

http://www.epa.gov/airtoxics/6h/6hpg.html

http://www.kpaonline.com/authorizedFiles/6H_Checklist.pdf

http://www.ppg.com/coatings/matthewspaint/forfabricators/epa6hrule/Pages/eparule.aspx

http://www.sherwin-automotive.com/sign-manufacturers/products-reference/reference/6h-requirements/

It may seem that all of these procedures, if done as recommended, could hinder productivity. However, making an SOP, attaching the appropriate time intervals and carrying them out as designed will save valuable time. Mixing room routines make a paint department more efficient and profitable by reducing the chance of color mismatches. With a well thought-out process, the variables that can be controlled will be.

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