basic spray gun help needed

erich weaver · #1 08-27-2007, 11:06 PM

I have no experience using paint spray guns, but thought I would give it a try applying primer on my fiberglass parts after tediously filling pin holes and sanding for what seems like forever. I followed the directions that came with the spray gun, which is a siphon cup type unit that I hooked up to my cheapo Craftsman air compressor. I practiced by spraying water on the hangar wall until I thought I had the hang of it, then disassembled the gun and dried it out. The next morning I mixed up the two-part primer (Eurofill from Evercoat) and gave it a shot.

Everything went great at first. I was amazed how smooth the first coat went on my wheel pants and I actually started having thoughts that I could eventually paint my own plane. But somewhere in the middle of my second coat things went to heck - not smooth at all. It looked like I had sprayed the dust from a pencil eraser all over. I stopped, dissassembled the gun and cleaned it all out. Started again on some new parts and got the same result - worked great for awhile and then got the eraser dust affect.

Nothing too tramatic here because the primer sands down really easily and nicely, but I dont want to do more until I understand whats going on. My guess is something pretty simple, and I dont think its the primer product - the part I got right was really nice.

Whats the deal?

thanks

Erich

Rivethead · #2 08-27-2007, 11:16 PM

So many things could be going on, but it sounds to me as if your primer is going off. How old is the mix you're using? Or is there water getting into the spray?

RV7Factory · #3 08-27-2007, 11:16 PM

Erich,

Since I seem to so much help to you on other things, why not try here as well.

I don't know if it will be of value, but I have a few links to spray gun set-up info on my Tips & Resources page. Look at the Priming & Painting section.

Good luck! BTW... no more info on our coversation of the other day - sorry.

K?hler · #4 08-28-2007, 07:00 AM

1. Clogged cup vent.
2. Too small gun nozzle & heavy primer build up.
3. Too small compressor / can't keep up / drops below set pressure.

Good luck.
-KK

Tbone · #5 08-28-2007, 07:26 AM

to me that your primer, which is an activated primer, has started to set up in the cup. Most modern primers are a two part or even some a three part. Make sure that you are using the correct temp reducer or correct ratio. I have some high performance primers and clears that are great to spray the first coat and then subsequent coats the product starts gelling in your cup. Hope this helps.

Regards,
Tbone

az_gila · #6 08-28-2007, 08:30 AM

Was the temperature increasing during the time in question? gil A

Guy Prevost · #7 08-28-2007, 09:13 AM

Here's my two cents.

I don't think your primer is drying in the cup.

Most spray guns come with a tip that is too small for spraying filling primers. I've had similar issues trying to spray PPG K38 without changing to a larger spray tip. The heavy fill primer begins to build on the needle and in the tip as you spray. Pretty soon, you get the spattering that comes along with a dirty tip. You might get away with thinning the primer more if the manufacturer says it's ok. If not, you'll need a bigger tip for your spray gun. If Sears doesn't make one, you'll have to get a gun that does have a range of tips available.

Most good paints and primers will recommend a tip size on their data sheet. Different sizes are required for conventional vs. HVLP setups.

Hope this helps.

Guy

erich weaver · #8 08-28-2007, 09:57 AM

Thanks for the tips guys.

I started spraying early in the morning, so the temperature was definitely rising as I worked, but judging on what I saw upon dissassembling the gun, I dont think the primer was setting up inside the gun or the siphon gup. Tip size might be the ticket, but Im not sure I have any options there.

Did a quick look at Brad Olivers tips from the website posted above and saw the reference to the Harbor Freight 43430 HVLP sprayer. Checked at HF site and its on sale for $30! - might have to give it a try.

Whats the difference between hooking up that HVLP gun to my compressor and using a "turbine" HVLP system like what was being offered for sale on VAF the other day (see http://www.vansairforce.com/communit...highlight=hvlp ) ? I assume they work differently, but not really sure what the difference is.

erich

RV8N · #9 08-28-2007, 11:36 AM

What temperature rating is your reducer? If your using reducer for 65 F and it warms up to 85 F, the reducer could be evaporating too fast.

Just a thought...

Karl

Steve · #10 08-28-2007, 12:03 PM

I had a similar experience when I was learning to use Variprime. It turned out I had the fluid adjustment set too rich. I was using a suction DeVilbiss freebee gun that came with my Delta compressor. It looked like I was applying flocking to a Christmas tree. I "leaned" out the mixture and lowered the air pressure a bit and all went well.

Steve