Don't spray paint/lacquer boxes in extreme hot weather!!!

[bluesdevil]

I live in South Florida (USA) and yesterday was 96 degrees with heat index well over a 100 and very sunny. Outside I was putting a clear lacquer coating over a bare aluminum enclosure that I sanded to a shine and the spray wasn't glossy smooth but rough powdery with what seemed like fibres!!!! I used the same can a few months ago in cooler weather and it was fine.  
   I should have known better because I BAKE enameled boxes in my oven around that temperature. This time of year I better do my finishing at night.
    Weird experience, just wanted to share.

[NaBo]

Yeah, I've been painting enamel on wood for the past ummm...  2 weeks?    With the heat and humidity here, its taking at LEAST 4 days for every coat to dry...  bluhhh.

[Paul Marossy]

Yeah, lacquer is pretty sensitive to humidity. Enamel takes a long time to dry even in very dry and climates, like where I live.  

[Paul Perry (Frostwave)]

Only a guess, but......... using a spray can, the propellant is pretty cold as it comes out, this might be condensing some of the (high) humidity in the air, giving tiny water droplets that mix in with the lacquer. This would match what you say it looks like.
Or, the lacquer could be so cold when it cots the surface, that moisture condenses straight onto it from the air.

You wouldn't have that problem in Melbourne Australia right now..

[Greybeard]

the spray wasn't glossy smooth but rough powdery with what seemed like fibres!!!!
   I should have known better because I BAKE enameled boxes in my oven around that temperature. This time of year I better do my finishing at night.
    Weird experience, just wanted to share.

    Yeah, this is what happens when the lacquer drys before it actually gets to the surface you are trying to spray. Happens with lacquer all the time in high heat. And never spray in direct sunlight. The other effect is called blushing, this is when humidity gets trapped in the finish, usually happens with acrylic enamels. Surface is usually nice and smooth but cloudy instead of clear.

    Years and years of painting first cars, and then guitars...... I've run into all the problems imaginable.

    Set up good lights and spray at night, as you said...... and leave any acrylic enamels for drier days..... Unless of course you are using spray gun and compressor, then you can mix and adjust you way to any situation.

Greybeard

[Ry]

I just noticed this last week as I was spraying primer on a box.  A fair percentage was drying before it hit the box.  I honestly wasn't too surprised, though, it was probably 113 or so on that Phoenix afternoon.

[Paul Marossy]

You wouldn't have that problem in Melbourne Australia right now..

Las Vegas, NV, too. In high heat, low humidity conditions, I find myself holding the spray can a little closer than I normally would to compensate for the quicker drying time. Things usually turn out well for me in the summer. I have a harder time in the winter when it takes longer for stuff to dry...  :?

EDIT: I was thinking. When I spray stuff in the summer (or winter), I am taking stuff from inside my house (~75 deg F) and then taking it outside just to spray and then hang to dry for a little while before taking it back inside. So, aside from a high ambient temperature (110 deg F or higher), the enclosure and paint/primer/lacquer/clearcoat are at room temperature. Maybe that helps to slow down the drying time enough to give me good results? With the average summertime relative humidity of less than 25%, humidity is not usually a problem for me.

[bluesdevil]

Thanks to all for posting comments. It was overcast today and a bit cooler so I gave it another try and went on wet and smooth..... also made sure I was in the shade this time!! Good luck to everybody finishing their boxes in  this hot as hell summer.

[Paul Marossy]

Good luck to everybody finishing their boxes in this hot as hell summer.

I sure hope this ain't that global warming thang deciding to stay for a while...  :shock:

[Greybeard]

I sure hope this ain't that global warming thang deciding to stay for a while...  :shock:

It is,...... but we have to learn to deal with it. :wink:

Greybeard

[brett]

Hi.
I use an infra-red thermometer to check the temperature of the surface that I'm painting.  (Got it from work at a good price :wink: ).  It's amazing how hot surfaces become if in sunlight, etc.  Not unusual to get 50C (x9/5+32=122F) under "normal" sunlit conditions.  Because your hand is 35C, the surface won't even feel hot (not until about 60C/140F !).

What you need to do is lose the radiative load (which will also greatly boost the local humidity, too).  Deep shade/at night works great, but make sure any lights you use have a glass front to reduce the infra-red (heating) component in the light.

Fortunately, the *absolute* humidy of the air usually stays about the same all the time (day and night, under lights, etc).  The *relative* (to saturated) humidity rises and falls quite strongly through the day and night.  In a lot of places, the relative humidity gets high enough at night to drop dew on your grass (about 100% humidity).  In any case, working at a surface temperature well above dew point (usually >15C/60F) and below 35C (100F) will usually do the trick unless the air is soggy wet or bone dry.

There's a simple test for humidity, too.  Take a bottle of soda out of the fridge (at about 5C/40F).  If no moisture condenses on it, there's bugger all moisture in the air.  If the bottle starts to dry off while it's still quite cool and pleasant to drink (15C/60F), that's good for painting.  If the bottle gets really warm (25C/85F) and it's still wet, the humidity might be too high for quick drying and a good finish.

cheers

[petemoore]

We have a weather dial, with temp, humidity, and barometric dial indicators on it.
 the laquer I have indicates the humidity must be below 60%, which seems accurate, if I spray when it's above the recommended H level for doing so, I get cloudy results.
 I haven't noticed that 'normal' heat [say below 150?] does anything but make the laquer dry faster.
 I preheat the box, spray, let dry, sand?...heat, respray.