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  #1  
Old 05-30-2011, 04:41 PM
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brockrwood brockrwood is offline
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Default Spray paint goes on "dusty" or "sandy"

OK, what am I missing?

When I paint a rocket, the paint tends to go on so that the finish seems like it has paint "dust" or "sand" on it, rather than a nice smooth finish.

What am I doing wrong? Not putting on enough primer? Using too much primer? Not sanding enough? Spraying from too far away? I am using standard Krylon white primer and Krylon flourescent yellow on top of that.

Any help appreciated. My 9 year old daughter, who used to think I knew everything about rockets, has now lost faith in my rocket painting ability.

Help! My "street cred" with my offspring is at stake!

- Brock
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  #2  
Old 05-30-2011, 05:15 PM
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The most common cause of a rough finish with rattle can spray paint is either being too far away or crazy low humidity. If the surface is well prepared and smooth (a very big if) then the issue with a spray is paint partially drying in the aerosol; small droplets dry prior to hitting the surface to be painted.

When the manufacturer provides the "hold can" distance it is usually appropriate for a well shaken/mixed product in the optimal temperature and humidity as referenced on the can. Check the painting conditions on most paints and there is a temperature range and a maximum humidity - Krylon and Rustoleum want it below 85%. If it is very, very dry then you will see little globules of paint drying on the surface as opposed to forming a paint layer.

Also make sure that the paint is really well shaken from a rattle can. As a resolution to this model try taking a 400 - 600 grit paper to the model and re-apply a coat when it is a little cooler and perhaps a little less dry.
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  #3  
Old 05-30-2011, 05:33 PM
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Red face

Thanks for the tips!

Yes, it is really dry here in Denver on most days but, oddly, it has been sort of rainy lately. I will try shaking it *really* well and holding it a bit closer. That is sort of what it seems like - the paint actually drying before it hits the rocket and then adhering as little dust particles.

I am starting to appreciate the "almost ready to fly" rockets with the pre-colored parts more and more as I sand and sand and re-paint and re-paint.

This is the free rocket my daughter got from Quest for joining the NAR. Maybe I should just slap the decals on it, stick a C6-5 in it, and push the button! No, my "do it right or don't do it at all" superego is taking over...

- Brock




Quote:
Originally Posted by jharding58
The most common cause of a rough finish with rattle can spray paint is
either being too far away or crazy low humidity. If the surface is well prepared and smooth (a very big if) then the issue with a spray is paint partially drying in the aerosol; small droplets dry prior to hitting the surface to be painted.

When the manufacturer provides the "hold can" distance it is usually appropriate for a well shaken/mixed product in the optimal temperature and humidity as referenced on the can. Check the painting conditions on most paints and there is a temperature range and a maximum humidity - Krylon and Rustoleum want it below 85%. If it is very, very dry then you will see little globules of paint drying on the surface as opposed to forming a paint layer.

Also make sure that the paint is really well shaken from a rattle can. As a resolution to this model try taking a 400 - 600 grit paper to the model and re-apply a coat when it is a little cooler and perhaps a little less dry.
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  #4  
Old 05-30-2011, 09:28 PM
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I find that I do most of my spraying from 4" to 8" away, not the 12" usually recommended. But low humidity is rarely a problem here...
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Old 05-31-2011, 08:38 PM
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If, like me, you do your spray painting outdoors, beware of breezes. Aside from the obvious, another problem they can cause is the one that you reported. My area always has variable winds that swirl around from random directions, so I have learned to wait for moments of calm when I paint. Early on though, I didn't always stop soon enough after the wind picked up again, and I got gritty paint coats as a result.

Another thing: apply the paint in one smooth steady stroke from end to end in one direction only, keeping the pace moderate and constant from beginning to end, and maintaining the same distance throughout. It often helps to start the spraying just ahead of the rocket and stop it after you have gone past the other end. Then rotate the rocket a quarter turn or so and repeat the process. Continue until the rocket is fully covered with an even coat. Jerking or jiggling the can around as you spray is another way to obtain a gritty coat and spattering of paint. Sudden movements cause momentary surges and ebbs in the amount of paint that is delivered to the nozzle. To lay down an even coat, you need to have a constant, even fan or cone of spray from the nozzle, and to deliver it the nozzle requires a steady flow of paint from the can.
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  #6  
Old 05-31-2011, 08:58 PM
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I'm right handed (when painting, at least) and I always try to stand with the breeze at my right elbow. That way, the paint goes toward the rocket (held in my left hand).
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  #7  
Old 05-30-2011, 06:39 PM
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...it obstructs my view of Venus...
 
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OK, I just re-painted with the can held about 1/2 the distance I normally use and it worked *much* better. No more dusty, powdery stuff! I think I was mis-judging the distance between the paint can nozzle and the rocket previously.

Paint problem solved by actually getting the paint onto the rocket before it dries in the air. Doh!

Thank you!

- Brock


Quote:
Originally Posted by jharding58
The most common cause of a rough finish with rattle can spray paint is either being too far away or crazy low humidity. If the surface is well prepared and smooth (a very big if) then the issue with a spray is paint partially drying in the aerosol; small droplets dry prior to hitting the surface to be painted.

When the manufacturer provides the "hold can" distance it is usually appropriate for a well shaken/mixed product in the optimal temperature and humidity as referenced on the can. Check the painting conditions on most paints and there is a temperature range and a maximum humidity - Krylon and Rustoleum want it below 85%. If it is very, very dry then you will see little globules of paint drying on the surface as opposed to forming a paint layer.

Also make sure that the paint is really well shaken from a rattle can. As a resolution to this model try taking a 400 - 600 grit paper to the model and re-apply a coat when it is a little cooler and perhaps a little less dry.
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  #8  
Old 05-30-2011, 06:37 PM
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Quote:
Originally Posted by brockrwood
OK, what am I missing?

When I paint a rocket, the paint tends to go on so that the finish seems like it has paint "dust" or "sand" on it, rather than a nice smooth finish.

What am I doing wrong?
Yes, as noted, you ain't getting it wet enough. You're shooting from too far away, and you're not putting enough paint on. It's gotta get it wet if it's gonna look good.

Trying hold the can closer and apply more paint. You don't want to dwell with the can - keep it moving. But come back over the same area with multiple passes to get it wet.

To avoid runs, apply a tack coat first. This is a light, sorta dry coat. Let sit for 10 minutes. Then apply a heavier second coat wherein you lay it on thick. The first coat, having partially dried, will help hold the second, thicker coat and prevent runs.

Then wait 10 more minutes. If it still needs paint - if it has some poorly covered areas - then apply a 3rd coat using the same techniques as the second.

HTH.

Doug

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  #9  
Old 05-30-2011, 06:43 PM
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...it obstructs my view of Venus...
 
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The people in this forum rock. You are all very helpful. Thank you!

My "street cred" with my daughter is saved!

- Brock
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