Paints & Coatings Resource Center

Ask the Expert Question-and-Answer Archive

by Ron Joseph

June, 2003

Airless Paint Sprayer Problems

Q. I am having problems painting a home that I just built. I'm using an airless paint setup (red dog??) which I borrowed from a friend. It is a large commercial unit. It has a Graco gun, which I have replaced the filter in the gun's handle (I believe the filter was a fine screen mesh) and the nozzle and orifice. I'm applying a oil based primer and a water based finish coat. I'm painting the exterior trim of the house which consist of natural cedar soffits, a pre-primed pine material for the gutter boards and gable rakes and a hardi-plank (cement-board) siding material for the dormer walls. The problem is :

  1. The gun keeps clogging up on me and I have to keep inverting the nozzle to clean it out. It will even clog when the tip is inverted! The finsh paint clogs more than the primer but they're both bad. I have experimented with thinning the water based paint down with water to various viscosotys with no luck. I've also played with the pressure (from 500-3000psi) the 3000 setting slows the clogging down but man does the paint go in thick!
  2. I'm getting a thick stream of paint along the edge of the fan pattern as well. I also borrowed a Wagner airless set-up and it seems to be doing the same thing.
Any suggestions would be appreciated.

A. It sounds like you really have got your hands full. Replacing the filter in the gun is always a good start, however I suspect there should be a filter near the fluid section on the pump. I am not familiar with "RED DOG" brand but I would expect to find another filter in this area, check it and be sure that it is clean. I also would expect to find a screen type filter on the end of the fluid stinger, or material pick up tube. If you do not find a mesh screen here, you can fashion a filter from window screen material, and clamp it on the stinger tube, and be sure that it is clean.

The paint you are using is typically very thick, and anything finer in filter material will not allow good flow of the paint, and may cause excessive clogging.

Next, lets look at the "reverse a clean" type tip that you are using. You didn't mention the size of the tip, this too will have an effect on the proper atomization of the paint, if the tip is too large, you will have heavy "tails" on either end of the spray pattern.

With paint that is heavy in viscosity, be sure to increase the fluid pressure to a good high pressure, such as 3000 psi. A tip in the range of .0015 to .0017 thousands should get the job done.

Now that we have all of the finer things out of the way, you state that you are using an oil based primer coat, and a water based top coat. These two materials are... just as they sound, (oil and water) they don't mix. The solvent in the oil based paint will turn the latex into something that resembles cottage cheese.

Be sure to clean the pump of all, and I mean all paint material prior to switching from one type of paint to the next. Without insuring the cleanliness of the pump, these materials will clog even the best of filters

As a rule of thumb, I always like to flush an oil based product with the proper thinner, and then I will use either isopropyl alcohol (IPA), or acetone to chase out any residual materials, these solvents will absorb infinite amounts of water and will prepare the system to be flushed with water, and yes you guessed it, then flush the system with water.

To reverse the process, then do just that. Flush the system with water, then alcohol, or acetone, then, and only then will the system be ready to switch between chemistries.

Please be aware that coatings and solvents are chemicals and therefore you should always pay attention to proper handling procedures and be prepared to wear protective clothing, such as respirators, gloves, coveralls, etc. For further information on the health and safety requirements for the coatings and solvents you wish to use we strongly advised you to contact your local coating supplier. If possible, go the extra step and look for this information on the website of the product vendor.


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