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What's the deal with humidity and spray painting?
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  1. #1
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    What's the deal with humidity and spray painting?

    So, I just sprayed a couple rockets. One with yellow lacquer (Lustrekote) and one with Rustoleum crystal clear enamel.

    Both sprayed fine and looked glossy initially but when I went back out to check on them both had turned matte almost chalky; both had a whitish cast to them. The enamel situation was the worst because it was over black paint so stands out. But basically the same situation on both rockets.

    Both cans have been previously used with great results.

    I'm presuming it's due to the humidity; it's ~70 degrees now and 80%+ humidity. OK, I'm an idiot for painting in high humidity and I'm regretting rushing things.

    But, what is it about the high humidity that makes paint that initially appears to go on fine and lay down nicely suddenly go all frosty on me?

    And, will a coat of Future cure it?

    Marc
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  2. #2
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    I can't answer your question but I can make a suggestion. What I did here in Michigan yesterday was spray in the garage, then immediately take them inside where it's air conditioned to dry.

  3. #3
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    Good idea; I actually considered this when I hit the enamel rocket with a second coat in hopes of curing it. But, the wife is sensitive to solvent smells and I have to keep things in the garage until they de-stink (generally, 2 days minimum for enamel and 1 day for lacquer).

    Sigh!
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  4. #4
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    You have a little more time to get enamel inside in the dry air than lacquer. I like lacquer better overall, but I have had to resort to enamels most of the time due to humidity. I can't spray and dash quick enough with the lacquer, even if I'm standing at the door. I can take my time with enamel, using the spray and stroll method instead of spray and dash.

  5. #5
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    I wait for dry days, paint in the afternoon or early evening (when the humidity is usually lower) and bring the model indoors afterward and set it up in a closed room. This works even though I don't usually have air conditioning and I don't have a garage. (Humidity is typically highest in the morning and then steadily decreases throughout the day - unless a storm front moves in.) In the absence of a garage, I think that it can also help to spray while standing on a paved slab (such as a dry driveway or the street) as opposed to out in your yard over the lawn or near large stands of shrubbery. Plants are living things and as such, they respire. One of the main things that they exhale is water vapor. Blades of grass are tiny, but when a few million of them are all together in an expanse of lawn, all of those minuscule respirations add up. And grass isn't the only living thing in lawns, either.
    Mark S. Kulka NAR 86134 L1, ASTRE 471, Adirondack Mtns., NY
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  6. #6
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    That's called blushing. The evaporation of the paint solvents causes cooling below the dew point which in turn causes condensation of water on your new paint job. If you would have a source of warmth in your garage (??? Box with hair dryer ??? portable heater???) somehow warm dry air, placing your rocket in that should prevent blushing. Best not to paint in high humidity.
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  7. #7
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    Ah! This blushing phenomenon sounds exactly like what I'm seeing then.

    Rather annoying, as I've spen two weeks gradually building and painting the model then I go and screw it up on the last step due to haste.

    It's a surface phenomenon... right? so a coat of future might cure it? Or a light wetsand?
    Thou shalt not violate causality within my historic light cone. Or Else.
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  8. #8
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    I really can't help you with this problem, I'm just inserting a link to my personal weather station here:
    http://www.wunderground.com/weathers...p?ID=KAZGOODY9

    Currently 107* and 8% humidity. Yeah, that's a single digit humidity and the sensor is over my little lawn.... We finally announced Summer this week, yesterday it was 112*. Like I said on the other paint thread, Lacquer dries really fast here.
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  9. #9
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    Quote Originally Posted by Marc_G View Post
    Ah! This blushing phenomenon sounds exactly like what I'm seeing then.

    Rather annoying, as I've spen two weeks gradually building and painting the model then I go and screw it up on the last step due to haste.

    It's a surface phenomenon... right? so a coat of future might cure it? Or a light wetsand?


    I've never used Future or wet sanded a finish coat, so I don't know either. I don't believe a coat of Future is going to help. Letting it dry and a recoat will solve the problem. The blush could be through out the thickness of the coat of paint.
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  10. #10
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    So, did I mention I'm impatient?

    Before starting my kids' baths, I decided to do a future experiment. The top coat of clear enamel had dried for an hour and a half, and since the clear dries much more quickly and less stinky than the color coats, it was actually dry to handle and not too smelly now.

    I grabbed the nose cone, figuring that if I REALLY screwed something up, I could sand down the thing fairly easily. No way I was risking the main model. Here's a pic of the model in question, BTW:

    Click image for larger version. 

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    Here's a pic of the dark fin areas shortly after the blush appeared:
    Click image for larger version. 

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    Note, it now is very "matte" but not so milky at all. Just dull.

    Here's the nose cone before my experiment with Future:

    Click image for larger version. 

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    So, I took this semi-dry blushy milky nose cone with a big sag mark that is extra milky, and coated it with Future. Left it for not quite two hours, then brought it up from the basement (the wife doesn't mind Future smell, by the way).

    It was a beautiful gloss black except for the milkiness around the sag/run in the paint. The whitish stuff you see on the left side is actually a mirror reflection kind of thing. It's deep black, just like black+crystal clear+future usually gives me.

    Click image for larger version. 

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    So, I'm going to leave the model until tomorrow night. There are two sag marks on it (harder to see, on yellow) and if they are still prominent I may slice them down with a very sharp xacto knife to reduce the thickness and thus the visible milkiness. Otherwise I'm just going to Future coat the model and call her done.

    As for the still visible issue with the nose cone sag, I'm gonna call that a learning experience. It may fade with time. I may lose the rocket (a two stager) on it's first flight... we may get taken out by an asteroid strike. If it still bugs me a month from now I'll sand the whole thing down to primer and recoat properly. Probably be bone dry, by then... no humidity to worry about (and probably burn bans, so no launching either!).

    Thanks to all for your support on this. I learned some things today.

    Marc
    Last edited by Marc_G; 24th June 2011 at 02:37 AM.
    Thou shalt not violate causality within my historic light cone. Or Else.
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  11. #11
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    Quite correct about the blushing...

    If you're in THAT big a hurry, I'd suggest you make a box out of plywood or something like that with a light bulb inside-- sort of a poor-man's drying oven... especially since your wife is sensitive to solvent odors... you can set that up in the garage, turn the light on a couple hours before you paint to warm the box up, paint the rockets and then set them in the box. The light bulb will heat up the air in the box somewhat and drive off the humidity, which should be just enough to prevent blushing (unless you're painting in the garage in a pouring rain). It doesn't take a WHOLE lot to prevent it, just either raising the temp or lowering the humidity.

    We used to keep an old refrigerator that didn't work anymore with a light bulb in it turned on all the time to keep our welding rods dry for the same reason-- it doesn't have to have a heat lamp bulb or anything like that; in fact that would probably be very counterproductive by producing too much infrared heat-- a standard 60 watt or 80 watt bulb is plenty.

    Good luck! OL JR
    The X-87B Cruise Basselope- THE ultimate weapon in the arsenal of homeland defense and only $52 million per round!

  12. #12
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    Quote Originally Posted by Marc_G View Post
    So, did I mention I'm impatient?

    Before starting my kids' baths, I decided to do a future experiment. The top coat of clear enamel had dried for an hour and a half, and since the clear dries much more quickly and less stinky than the color coats, it was actually dry to handle and not too smelly now.

    I grabbed the nose cone, figuring that if I REALLY screwed something up, I could sand down the thing fairly easily. No way I was risking the main model. Here's a pic of the model in question, BTW:

    Click image for larger version. 

Name:	Blush00001.jpg 
Views:	205 
Size:	221.9 KB 
ID:	51504

    Here's a pic of the dark fin areas shortly after the blush appeared:
    Click image for larger version. 

Name:	Blush00002.jpg 
Views:	247 
Size:	156.3 KB 
ID:	51505
    Note, it now is very "matte" but not so milky at all. Just dull.

    Here's the nose cone before my experiment with Future:

    Click image for larger version. 

Name:	Blush00003.jpg 
Views:	225 
Size:	178.7 KB 
ID:	51506

    So, I took this semi-dry blushy milky nose cone with a big sag mark that is extra milky, and coated it with Future. Left it for not quite two hours, then brought it up from the basement (the wife doesn't mind Future smell, by the way).

    It was a beautiful gloss black except for the milkiness around the sag/run in the paint. The whitish stuff you see on the left side is actually a mirror reflection kind of thing. It's deep black, just like black+crystal clear+future usually gives me.

    Click image for larger version. 

Name:	Blush00004.jpg 
Views:	226 
Size:	281.5 KB 
ID:	51507

    So, I'm going to leave the model until tomorrow night. There are two sag marks on it (harder to see, on yellow) and if they are still prominent I may slice them down with a very sharp xacto knife to reduce the thickness and thus the visible milkiness. Otherwise I'm just going to Future coat the model and call her done.

    As for the still visible issue with the nose cone sag, I'm gonna call that a learning experience. It may fade with time. I may lose the rocket (a two stager) on it's first flight... we may get taken out by an asteroid strike. If it still bugs me a month from now I'll sand the whole thing down to primer and recoat properly. Probably be bone dry, by then... no humidity to worry about (and probably burn bans, so no launching either!).

    Thanks to all for your support on this. I learned some things today.

    Marc
    Looks pretty good.

    Couple points...

    1) if the paint still smells, even if it's dry to the touch, it's not "dry" yet-- meaning it hasn't cured. The 'paint smell' is solvents still escaping from the coat-- they need to be able to outgas or you may get blisters or peeling paint or other such problems. Hence the recoat time limitations and "fully cured in X days" warnings on the back of the paint can.

    2) When spray painting, put on 3-4 light coats instead of 1-2 heavy ones, and you will eliminate those runs before they happen.

    3) Practice your spray painting technique-- keep the can moving at all times, and try to keep it an even distance and perpendicular to the surface, and moving at the same speed during the entire paint stroke-- start spraying before getting to the rocket, and continue on past it a bit before reversing for the next stroke. Remember, you can't hardly move the can "too fast" but you can DEFINITELY move it TOO SLOW, which causes runs, sags, and drips, and other such unsightly problems that ruin paintjobs.

    4) Don't get in TOO big a hurry-- there are places and ways to cut corners and save time-- spray painting isn't one of them if you want a nice finish. (Neither is prep work-- the better your prep, the better the final paint job will be, so long as you DON'T RUSH THE PAINT APPLICATION and ruin your hard prep work!)

    Good luck and that's a nice looking Vigilante-- I've got one on top of the cabinet in the other room that needs a rebuild-- flew it during my pre-BAR days back in the late 80's and the poor thing was a victim of a high-schooler's lack of building skills and rush to get it painted and flying...

    Later and have a good one! OL JR
    The X-87B Cruise Basselope- THE ultimate weapon in the arsenal of homeland defense and only $52 million per round!

  13. #13
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    Quote Originally Posted by luke strawwalker View Post
    3) Practice your spray painting technique-- keep the can moving at all times, and try to keep it an even distance and perpendicular to the surface, and moving at the same speed during the entire paint stroke-- start spraying before getting to the rocket, and continue on past it a bit before reversing for the next stroke. Remember, you can't hardly move the can "too fast" but you can DEFINITELY move it TOO SLOW, which causes runs, sags, and drips, and other such unsightly problems that ruin paintjobs.
    Can't move the spray can too fast? Sure you can - it causes the nozzle to "spit" paint and any spray mist that does come out has a tendency to produce "gritty" coats. Use a steady, moderately-paced speed, keep the nozzle the same distance from the model's surface throughout, spray the surface at a 90° angle (not tilted up or down the rocket) and make spray passes in one direction only. (Don't reverse direction and come back the other way during a single pass. If you want to make a spray pass in the opposite direction -- rarely needed, by the way -- do it in a completely separate pass.) Otherwise, excellent advice.

    (As I said, I have a lot of opinions about even the finer points of spray paint technique. ) Use these suggestions as a starting point, though, Marc_G; eventually you will probably develop your own style, if you haven't done so already. And then you'll come back and give me tips on improving my painting technique (I hope).
    Mark S. Kulka NAR 86134 L1, ASTRE 471, Adirondack Mtns., NY
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  14. #14
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    I'm pretty embarrassed about the sags and runs.

    I rarely get them these days, but then again I've mostly been using lacquers and have kind of gotten the hang of those fast-flash-off paints. The sags I got yesterday were in areas I had recoated assuming a certain amount of drying had occurred, which would have been the case on lacquers but not enamels.

    My painting hand is much steadier these days but sometimes I still screw up.

    On the bright side, overnight the sag on the nose cone became much less milky as the curing progressed. I'm letting the rest of the model sit in the garage today and tonight will Future coat it. All signs point to a launch window tomorrow morning!

    Marc
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  15. #15
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    Quote Originally Posted by MarkII View Post
    Can't move the spray can too fast? Sure you can - it causes the nozzle to "spit" paint and any spray mist that does come out has a tendency to produce "gritty" coats.

    I said "Can't HARDLY move the spray can too fast"... thanks for the misquote Mark...

    The biggest mistake starting painters using rattlecans or other spray paints/equipment is moving the can/gun TOO SLOWLY, which puts too much paint too thick in one spot. OBVIOUSLY if you whip the can all over the place so fast that it's blowing propellant gas out of the nozzle instead of paint you're moving it too fast (only way I can think of to get blobs and dry spray from "moving too fast"). Better to move the can a little faster than someone might think "optimum" than move it too slow. Better to put a little bit lighter coat on than one might think than put too heavy a coat on. Better to put an extra coat or two on than a heavy one that runs or sags.

    If you get TOO far away from the rocket, you'll start getting a pebbly surface from paint that won't flow out (dry spray) or only get the larger droplets hitting the surface-- the smaller ones will swirl off uselessly as overspray... the heavier droplets that can better 'penetrate the wind' will be the only thing hitting the rocket. Both conditions lead to "orange peel" finishes, which is not good. BUT, if you get the can/gun TOO CLOSE to the rocket, you're MUCH more likely to get runs and sags too, because the paint is TOO CONCENTRATED in one spot.

    That's all I was getting at...

    Have a good one! OL JR
    The X-87B Cruise Basselope- THE ultimate weapon in the arsenal of homeland defense and only $52 million per round!

  16. #16
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    Im Sooooooooo glad that I live in the west where there is no Humidity. A medium coat will usually dry in about 5-10min.
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  17. #17
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    So, the worst of the cloudy/milkiness went away over night, and the relatively matte surface was cured by a good coat of Future.

    Picture and maiden launch video are in this thread.

    Thanks for all your help folks!
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  18. #18
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    Quote Originally Posted by luke strawwalker View Post

    I said "Can't HARDLY move the spray can too fast"... thanks for the misquote Mark...

    That's all I was getting at...

    Have a good one! OL JR

    The X-87B Cruise Beagelope- THE ultimate weapon in the arsenal of homeland defense and only $52 million per round!
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  19. #19
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    Quote Originally Posted by bradycros View Post
    The X-87B Cruise Beagelope- THE ultimate weapon in the arsenal of homeland defense and only $52 million per round!
    Now that's funny right there-- I don't care who ya are... LOL

    Later! OL JR

    PS... Homeland SECURITY... another form of pernicious gov't waste more interested in harassing it's own citizens than those seeking to come here illegally (and do us harm).
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  20. #20
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    I have a question. I had some carbon tubeing that I just wanted to clear coat. When first sprayed it looked great. Than a day or 2 later the nice clear finish would just start to cloud up. I even sanded it off and started over the same thing happened.
    Thanks

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