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Primer by Don Hipskind
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Don Hipskind answers aircraft painting questions in the AXIS HVLP Paint Discussion Board.  He operates AXIS Products -  makers of HVLP Paint Sprayer and Fresh Air Breathing Systems.

For the kind of products you will be using and the kind of painting you will be doing, you won't need to change needles and nozzles. The 1.0 mm will do a nice job atomizing the products with an HVLP three stage turbine delivered to the spraygun through 40' of airline or less. So lets not complicate the process by changing needles and nozzles. You will need to keep the spraygun clean between sessions, however, and this is accomplished by pouring out the material from the paint cup and adding about 1/4 of the cup with lacquer thinner. Spray this thinner through the gun until the spray is clear - then remove the nozzle from the gun and clean in solvent and replace. Don't let paint dry in the spraygun! You will never get it all out if it dries and specs will continually come out of the gun in future paint applications.

Now that you have the wash primer on it's time to apply the primer. Various types are available but most prefer a good quality epoxy 2 part primer like DuPont DP 40 or similiar. It is easy to apply and provides an exceptional tooth for the base coat to grab onto.

What's the primer do? It has two primary purposes - it fills in minor defects in the surface to be painted and it acts as a magnet for holding on the base coats by absorbing some of the topcoat material into itself. This absorbtion quality doesn't just absorb paint, however, it will absorb dust, oil and other contaminants from the air so it is necessary to get the topcoat on to it in a short period of time - usually within 24 - 48 hours. Also, if you wait longer than that time, you will need to sand the surface of the primer because it hardens with time.

Every painter has his/her own techniques for spraying and the following recommendations are what I do - others will have their own opinions which they are free to discuss here but I select a good epoxy primer which is either dark green or gray in color. This is because the first base coat color I put on is white. I choose white because pastel colors look much more vibrant when they have a white undercoat. And when I use a dark primer I can easily see where I am going when apply the white material.

I mix the primer according to the directions on the paint can except that when using HVLP turbines I need to keep one feature of the turbine in mind - The turbine air gets hot!. This heat evaporates thinner which must be compensated for. This alone is the single most mis-understood fact about spraying with HVLP turbines. If not addressed you will get the dreaded orange peel - no doubt about it.

So we need to add more thinner to the paint to compensate for this loss and a good rule of thumb is 30% more!!! I recommend that after mixing test a sample of it on a test panel - then, when you have achieved an ideal mix get out your Zahn cup and time the mix. Future batches will be not require testing once this is achieved.

Now that you have a proper mix and you have all the necessary protective gear on and your mask is supplying a comfortable amount of fresh air to your lungs, you're ready to go. Stretch out the hoses to the work area so they won't kink around any obstructions and you're ready to begin. Remember - hold the gun about 8" from the surface and keep your wrist locked. Your shoulder will move the gun from side to side and up and down keeping it the same distance from the surface at all times.

We have already talked about adding more thinner to the paint which is the first all important requirement when spraying with HVLP and now the second requirement:

Spray on a mist coat first:

more later....don


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