Airbrushing & Conditions

[Dave G.]

10 hours ago, TransAmMike said:

Phew, you guys sure have my old head swimming with all this.  My rule of thumb, and I paint in my garage, is humidity in the 60's and temps around 85 and below in the garage. Can't say my paint jobs are substantially affected tho. BTW, I use Createx and craft paint.    Interesting but somewhat confusing info....at least for me.

If you're using my thinner I mentioned to you for craft paint in that more humid weather you can cut back on the retarder to 4 drops for 3 oz of thinner. You may still want a hair dryer handy as the paint flashes off very slowly in humid conditions. I still can't speak for Createx, never used the stuff personally.

The problem in high humidity is generally speaking with lacquers Mike.

Edited September 7, 2021 by Dave G.

[TransAmMike]

4 hours ago, Dave G. said:

If you're using my thinner I mentioned to you for craft paint in that more humid weather you can cut back on the retarder to 4 drops for 3 oz of thinner. You may still want a hair dryer handy as the paint flashes off very slowly in humid conditions. I still can't speak for Createx, never used the stuff personally

Yes Dave, I do use your concoction with the craft paint, but the Createx thinner with the Createx.  Thanks Dave

[Pete J.]

15 hours ago, peteski said:

I have to disagree with you Pete about just "some moisture".  Any air-conditioning unit (windows or central AC at home, or a car AC) remove quite a bit of moisture from the air.  That is why the older windows AC units dripped water on the outside, and a car AC drips water onto the street.  Newer window AC units don't drip because the moisture condensed on the evaporator side gets splashed on the condenser side (evaporative cooling) to make the AC units more efficient. 

Further proof is that dehumidifiers are basically same construction as a window AC unit, except the evaporator and condenser coils are placed back-to-back.  When the ambient air is first forced to travel through the cold evaporator, the moisture condenses on it. Then the cooled (but dry) air travels through the warm condenser coils, warming it to slightly above room temperature.   While you are correct that AC does not remove all the moisture, it removes much more than just some moisture.

I have a window AC in my bedroom and also a hygrometer.  In my area summers can get quite muggy (dew point in the mid-70s).  When the AC compressor cycles on and off, I can see the swing in relative humidity.  Of course for the AC to remove moisture out of the air, that moisture has to be there in the first place.  In a desert climate, where the air is hot and dry, the dew point is low, and there is very little moisture to be removed.  So in that climate, AC does mostly just cool the air.  But in areas where the ambient air is hot and very humid (like the summers where I live), the dew point is high, and AC sucks a lot of moisture from the air.

Pete, the purpose of my remarks was not to get into a protracted discussion about how a/c works.  I was only making the point that relative humidity is a direct function of the moisture in the air and that airs temperature.  High relative humidity directly relates to the likelihood of blushing and relative humidity is a direct function of temperature and the moisture in the air.  Given two identical masses of air  and identical amounts of water in suspension in the air,  the one with the lower temperature will have a higher relative humidity and is more likely to blush lacquer.  

  Having said that temperature is directly related to a plethora of issues with paint.  The moisture in the air causing blushing is only one of them.  I am only advocating for the use of a hygrometer to measure relative humidity as opposed to using dew point as a hard figure for go/no go for spraying lacquer.  

  The factors involved in painting have lead many to suggest that good painting is a black art.  There are more than a dozen factors that I can think of that will impact the outcome of painting.  You can adjust for two of the major ones by using a hygrometer/thermometer.

For most beginning users of airbrush's I have always been a big advocate  for using a journal.  Each time you paint, record the type and brand of paint and thinner, the rate of thinning, which airbrush you are using if you have more than one, the pressure you set your compressor at, temperature and humidity and the outcome of the job.  If you do this over time, you will start to see the effects of these factors on your outcome.  From that you can determine what adjustment you need to make for different conditions. 

Edited September 7, 2021 by Pete J.

[70 Sting]

@Pete J. That’s pretty much what I’ve been doing. Testing paints, thinners, ratios, pressures, distances, speed and taking notes. I’m just starting to get a handle on temperature and humidity. 

[Pete J.]

4 hours ago, 70 Sting said:

@Pete J. That’s pretty much what I’ve been doing. Testing paints, thinners, ratios, pressures, distances, speed and taking notes. I’m just starting to get a handle on temperature and humidity. 

Good deal.  You are well on your way to being a skilled painter. 

 One piece of advise. Scientific methodology suggests that you never change more than one variable at a time.  If you understand temp and humidity, then the next would be thinner ratios.  Understand that all thinners are not created equally.

  Many years ago when they still painted cars with lacquers, the paint stores sold different "temperatures" of thinner to allow you adjust for the temperature of the paint booth.  If you switch from one manufacture to another you really don't know what you are getting. 

Stick with the thinner by the manufacture until you are sure what thinning rate works in what temperature.  Also, you may be tempted to buy a gallon from one the hardware store.  That is great for cleaning the brush but it is not formulated for the paints we use. 

I know this will sound crazy to some, but I have several gallons of PPG automotive thinner that cost about $100 a gallon.  I bought it when I ran out of DuPont thinner.  I use it exclusively to thin paint and now have a very good idea of thinning rates for a given paint, temperature and humidity.  It is also very consistent in formulation. If you look at the MSD for Kleen Strip you will find that it can vary from pure acetone to who what knows.  As I said great airbrush cleaner but in my world, not useful for anything else. 

Good luck!