Spray Ultra High Build (UHB) Coatings Easier

There are several Ultra-High Build (UHB) Coatings that are applied today

UHB coatings are typically Amine epoxies, have a 2:1, 3:1, or 4:1 mix ratio, are 95% to 100% volume solids, have a pot life of 20-45 minutes at 25°C, and are applied to a coating thickness gauge (DFT) of 500 - 3000 microns.

These coatings are often applied as tank linings, or on marine structures, structural steel and as various other protective coatings, with a long (10+ years) service life requirement. It is these coatings we are discussing today.

Ultimately, the best solution for spraying Ultra High Build coatings is a plural component sprayer. Should, however, UHB coatings have to be sprayed with standard single-leg machines.

12 tips to help ensure a successful job

Graco Merkur Unit
  1. Select the right size pump.

    We recommend a minimum 56:1 sprayer. High pump ratios (68:1 and 80:1) provide high pump output pressure which is valuable if the airless hose lengths are long, however, the higher output is at the expense of flow.

  2. Gravity feed material.

    Feeding viscous coatings by gravity from a hopper rather than relying on suction to pick them up is always more successful in getting the pump to prime. Use ½" fittings and hose for best results. If a hopper isn’t available immerse the pump directly into the paint pail.

  3. Use the correct size filter.

    Some filled coatings (eg, glass flake) should be sprayed with no filter at all. For all other UHB coatings use a 30# pump filter without a gun filter.

  4. Pump coating within the correct temperature range.

    This would normally be between 20°C and 30°C. Low temperature causes viscosity problems. During cold weather keep coating in warm room before use. High coating temperature can cause reduced pot life and coating may set in the spray lines. (Reference tip 8)

  5. Use correct size airless hose.

    For optimum results use the largest diameter possible hose and keep length short. For most UHB coatings use 1 x 15m 3/8" ID material hose and a ¼" ID whip hose. For extremely high viscosity coatings or multiple hose lengths use a ½" hose, N.B. a ½" hose has one quarter of the pressure loss of a 3/8” hose.

  6. Use the correct gun.

    Recommended guns are high-flowing pressure guns that can be recommended by Blast-One, depending upon pressure used. Filled coatings may require the use of the gun that has no fluid tube, the paint hose connects directly to the front of the gun.

  7. Use the correct size tip.

    When spraying UHBs, the use of large tips with a high flow rate causes pressure drops and can give poor atomization. A 21–25 thou tip will give the best atomization for most UHB coatings. Certain very sticky coatings may need heavy duty tips.

  8. Heat coating with extreme care.

    While heating a coating will increase spray-ability, it is fraught with danger. If unavoidable, use the lowest possible temperature. Check the manual to ensure correct heater set-up and flush lines immediately after spraying with flush, cool material or solvent. Blast-One can advise you on how to make all the difference to a spraying job, by using heat correctly.

  9. Use a high ‘cut’ solvent.

    Do not use ‘gun wash’ thinners for clean-out. Use a solvent with a powerful ‘cut’ such as Graco Mekur. Consult with your coating supplier to select the correct clean-up solvent.

  10. Clean the entire system thoroughly at the end of your shift.

    At the end of the shift, some of the UHB material may have partially cured inside the hopper and suction elbow. To clean these out either dissemble and push a rag through the hose or attach a hopper clean-out assembly (available from Blast-One) to the gun, set the pump to low pressure, pull the gun trigger and feed the hose down the hopper through to the intake valve. Note also that larger diameter hoses are harder to clean than smaller hoses. To overcome this, flush hoses at the highest possible pump speed (40+ double strokes/minute) with the tip removed from the gun.

  11. Clean hopper of previous batch of material before filling with new batch.

    Before adding fresh mixed material to hopper, scrape or brush the sides to push down to the inlet any of the previous batch. If you are using suction feed, change supply pail every second batch.

  12. Flush pump throughout shift.

    As UHB coatings do not contain solvent, they do not ‘self flush’. If the pump is not flushed throughout the shift, some of the first mix may remain. To prevent this flush the pump at least once every two hours, more frequently for short pot life materials - ‘push’ the last few litres of coatings through the line with solvent, when solvent appears at the gun, recirculate and flush.

There are four key advantages to these types of systems:

  1. No pot life problems.

  2. Product heating for reduced viscosity.

    By reducing viscosity 'sprayability' is increase and in turn, less solvent is required.

  3. Reduction in material waste.

    By mixing material as it is applied, the only waste at the end is what's left between mixer and gun, not 1/4 to 1/2 a kit as is commonplace when 'hot potting'.

  4. Elimination of off-ratio mixing.

    One of the most common causes of coating failure and waste is incorrect mixing ratios. The electronic controls in plural component sprayers ensures material is always dispensed at the correct ratio. Should it start to go off-ratio, the machine will either shutdown or alert you.

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