How to Spray Inorganic Zinc Primers

It's more about how you handle the material, than what pump you use. Mixed primers weigh 20-30 lb/gal. Inorganic zinc is basically powdered zinc metal mixed into a base fluid that has no organic resins to keep it in suspension. This is done because the goal is to apply the zinc in such a way that it is laid down touching all the other zinc and the substrate metal.

The great corrosion protection is achieved only if the sacrificial zinc is conductive to the metal substrate. Epoxy or polymer binders significantly reduce that conductivity from happening. That's the difference between the inorganic and the organic zinc coatings.

From a fluid handling standpoint, the material must be fully conditioned into suspension, and then kept in suspension throughout the time it is in the pail, pump, hose, and gun. If it is allowed to settle, or get strained across a ball and seat, it won't matter what equipment you are using, you will have problems. 

1. Don't mix the zinc in until you are ready to spray
2. Be ready to spray the enitre batch without stopping
   
3. Avoid having the gun too much below or above the pail, as gravity will settle the zinc in the hose
4. Use a 3/8" ID hose x 50' max length and a short whip
   
5. Avoid sharp elbows on siphon or outlet fluid lines
6. Use a 30-60 mesh max filtration on pump or gun

1. Use a powerful mixer - at least 3/4 HP drive with a 5" Jiffy-type mixer
   
2. Slowly add the powder and continue mixing for 5 minutes after the powder is in
3. Strain the mixed fluid through a 30 mesh screen
4. Mix it for another 5 minutes
5. Keep the mixed fluid under agitation until you are done spraying and ready to flush

1. Start with the spray gun off of the hose
   
2. Load and circulate fluid through the hose and back to the supply pail at low pressure
3. Connect the gun and add enough pressure for a pattern
4. Spray

If you have to stop spraying, relieve the fluid pressure on the pump, hose, and gun. When a pump ball is holding pressure across the seat, there will be zinc particles trapped between the ball and seat. The difference in fluid pressure across the ball and seat will strain the solvent out, collecting many zinc particles at that point. This causes two failures:

1.     Packed out particles plug the passage and restrict ball movement.

2.     Some particles keep the ball from fully seating resulting in high velocity "wire draw" failure of the ball and/or seat.

This applies to any valves in the system, pump checks, any ball valves, and the spray gun. Even for short stoppages, relieving fluid pressure and/or low pressure circulating, goes a long way toward keeping things working well. Flush as soon as you are done spraying.

Flushing tends to wash the zinc out of suspension even more. Don't let it sit in the pump. Flush at a fairly high velocity to clean out the dead areas. Remember, velocity cleans, not pressure.

1. Circulate the flush back into the pail with the agitator off, and the siphon pick-up tube up off the bottom
2. Finally, dismantle and clean the lower to get any packed zinc off of the checks and packings
   

Graco Xtreme lowers are the best to use for these materials, mainly because they are easier to knock down and clean or service than the competitors' pumps. None of the our competitors offer pump lowers with better balls, seats, or rod and cylinder coatings than Graco offers, but some of those models are much harder to service.

If the balls are the failure point for particular inorganic zincs, we do offer ceramic balls that will hold up somewhat better. The seats are already carbide and are extremely hard. Seats and balls should always be replaced together. The balls may look much worse, but the smallest wear on the seat will allow some leakage, and quickly start tearing into a new ball. The image above shows an example of a heavily damaged inlet ball check.