620.11 Guidelines for Using Water-Borne Traffic Paint
From Engineering Policy Guide
Support. Special care must be taken when using water-borne (sometimes referred to as water based) paint in your equipment.
620.11.2 Handling Paint
Guidance. During loading procedures, special care must be exercised to prevent air from entering the material system. A water source should be at the loading facility to flush the area with water before loading and then flush any spillage after loading.
Thermostats on the bulk storage tanks should heat the paint from 40° F to 50° F with a safety device to prevent paint from being heated beyond this temperature range.
Standard. The manufacturer's maximum paint temperature of 160° F shall not be exceeded. Brass and copper will cause a chemical reaction with the heated water-borne paint. All heat exchangers and ball valves shall be stainless steel.
620.11.3 Daily Maintenance
Standard. The tanks shall not be run dry. An empty tank allows air into the system causing a "tree ring effect" and, after this happens several times, the system shall be completely torn down and cleaned. After each daily use, gun shrouds and fan atomizing assemblies from paint guns shall be removed, and cleaned with water and a soft brush. The fluid tip of the guns shall be cleaned with a wet rag or brush.
For overnight storage, the paint tanks shall be completely filled with paint. If it is necessary to prevent paint surface drying (skins) by pouring some water (1 pint) on top of the paint after the truck has been parked, the amount added shall not exceed that small amount because more water will change the paint formulation and affect drying time and durability.
Water shall be injected into heat exchangers only during cleaning, this is important. Exchangers shall be left full of paint. It is necessary to turn off glycol to the heat exchanger prior to daily shutdown to allow paint to cool in the exchanger.
Guidance. You should check for skins on paint in tanks before starting each day.
620.11.4 Weekly Maintenance
Standard. Water shall be flushed through the heated hoses and out of the paint guns for weekend storage. The strainer shall be cleaned at discharge of heat exchangers.
620.11.5 Periodic Cleaning
Standard. The paint strainer shall be removed at discharge of paint tank, cleaned and replaced, and filled with paint to remove trapped air after flushing entire system with water. Also, the heat exchanger shall be cleaned at this time.
Guidance. This should be done every two weeks of operation, or more often if needed.
620.11.6 End of Season Cleaning
Support. Over a period of several months of normal operation, paint will gradually settle in the heat exchangers. It may harden or remain a putty-like condition which will plug the tubes and interfere with normal paint flow. The heat exchanger cover can be easily removed and the ends unbolted.
It might be necessary to scrape off the paint build-up on the tanks and agitators.
Standard. The complete paint system shall be flushed thoroughly with water. All drain plugs shall be removed to prevent settling of solvent and paint in low spots.
The ends of the heat exchanger shall be removed and inspected to determine if additional cleaning is necessary. The exchanger ends shall be removed by pulling them directly away from the body not by sliding them.
After inspection, the heater shall be blown out, washed in water and reassembled using new gaskets.
Guidance. Some heat exchangers have small reinforcing pins and the tube sheet dividers which are designed to help hold the gasket in place and these can be bent or broken. The tubes should be individually routed clean.
The exchanger should be pressure tested (100 psi) for damaged tubes. Any tubes that leak air should be silver soldered shut at both ends.
If possible, the bulk storage tanks should be emptied with no winter carry-over of paint. The entire system should be flushed with water and the entire paint residue scraped off, if necessary.
620.11.7 Hazardous Waste
Support. Water-borne traffic paints currently used by the Missouri Department of Transportation do not contain lead, chromium, cadmium or barium and are, therefore, not considered hazardous waste material.
Standard. While water-borne paint is not a hazardous waste, it can cause environmental concerns when spilled. Care shall be taken to assure that any spilled paint does not leave MoDOT property. This includes water that may be mixed with the paint during clean up and becomes colored.
Support. Water-borne paints used by the Missouri Department of Transportation are not flammable. Therefore, sprinklers are not required for inside storage, nor do we need warning plaques on the striper.
Support. The shelf life of currently approved material is nine months. Water-borne paint consists of acrylic vehicle suspended in a water emulsion. As a result, the materials can freeze in cold weather. When the paint looks like cottage cheese, it is out of condition. If water-borne paints go out of condition, it is not recoverable.
Standard. Materials shall be stored where they will not freeze (40 degrees Fahrenheit maintained). If the paint freezes, it is not usable or recoverable and shall be disposed of properly.
620.11.10 Cleaning Solvents
Support. When wet, water-borne paints can be cleaned with plain water; therefore, the main cleanup solvent is clean water. When the paint is too dry for water to work, general household cleaners such as "Fantastic" can be used.
620.11.11 Application Temperatures and Dry Times
Support. Water-borne traffic paints, both normal and high-build, cure by a two-stage process. In the first stage, the water evaporates and the acrylic emulsion coalesces. This evaporation is dependent on temperature and humidity. Low temperature and high humidity gives longer dry times. In the second stage, the acrylic polymer cross-links to provide a durable film. This reaction is dependent on the air and surface temperature. 50° Fahrenheit is the recommended minimum application temperature on minor roads. Below 50° Fahrenheit, the polymer will cross-link (down to 35° Fahrenheit) but the durability of the film will be severely reduced, i.e. 2 to 3 months instead of 9 to 12 months. On major roads, the recommended minimum application temperature is 60° Fahrenheit. Cold weather paint traffic paint is also dependent on the air and surface temperature. However, due to the formulation of the paint, it is capable of being applied at air and surface temperatures of 35° (and climbing).
Dry times are dependent on temperature and humidity. Under conditions of 75° Fahrenheit, sunny and light wind, this material will dry to no-track in less than two minutes.
If materials are applied below 50° F, extended dry times might be a problem
Thick applications retard dry times.
Standard. Material temperatures shall not be increased in an attempt to get faster dry times.
Support. Water-borne traffic paints are sensitive to wet pavements and rain. Best results are obtained when pavements are dry (24 hours since measurable rain) and no rain occurs for 4 hours after application. As we cannot control the weather, here are some reasonable rules of thumb:
- A. Do not stripe on visibly wet pavements even though it has not rained recently.
- B. Lines need an hour to dry before any rain. If it looks threatening, don't chance it. You may have to repaint.
- C. If it does rain a significant amount, wait until the next day before trying again.
- D. Salt and other deicing chemicals need to be washed off prior to applying water-borne traffic paints. Additional time is typically needed to remove all the chemicals from the rumble strips.
620.11.13 Material Temperatures
Option. For best results, water-borne paints may be heated to 100° F + 10° F.
Support. Viscosity is very dependent on material temperatures as is ease of spraying. Excess temperatures will jell the paint with disastrous results; you might have to replace the heat exchangers.
Standard. The paint system shall not exceed 160° F anywhere.
620.11.14 Existing Markings
Support. Water-borne paints have not exhibited problems when applied over old markings.
620.11.15 Wash Water
Support. As discussed above in Hazardous Waste, the water-borne paint used by MoDOT is itself not considered a hazardous material. However, any paint or water that is colored by paint can be an environmental concern. Care must be taken to assure that any spilled paint or paint wash water does not flow off the surface of any MoDOT property.
Guidance. Bulk paint facilities should have a containment system for controlling paint spills and wash water. These systems consist of a hard surface at the bulk facility that drains to a settling tank and a separating tank. These tanks are used to allow the wash water to settle out the solids from the paint before discharging to the city sewer system.
Standard. The settling tank and separating tanks shall be monitored and cleaned when needed. At a minimum, a properly licensed company should clean these tanks on an annual basis. Keeping these tanks properly maintained is of utmost importance to be able to discharge into a city sewer system.
Guidance. Care should be taken to minimize the infiltration of rainwater into these systems to reduce the volume of material.
Option. If discharging into a city sewer system becomes a problem, arrangements can be made for other disposal of wash water. If this happens contact the Traffic Division for further assistance.