If you have sprayed flat top coat on a cold or rainy day, you probably have seen a layer of frost appearing, as shown in these heart breaking pictures:
This is called BLUSHING: A milky appearance of a topcoat caused by high humidity where water condenses on or in the wet coating. This can be eliminated by use of heat or a slower solvent or retarder. (http://www.sharpe1.com/sharpe/sharpe.nsf/Page/Paint+Terminology)
It appears that temperature (<13°C) and humidity (>90%) are the two major contributing factors. I have done several things in the past and try to solve this issue.
It appears that temperature (<13°C) and humidity (>90%) are the two major contributing factors. I have done several things in the past and try to solve this issue.
Addressing Temperature Factor: Keep It Warm
Addressing Humidity Factor Method 1: Using Semi-Gloss / Gloss Top Coat
Spray a thin layer of semi-gloss or gloss should do the trick. Note this is just a quick fix. In my experience, applying another coat of flat afterwards will unfortunately bring back all blushing.
So, flat no more.
So, flat no more.
Addressing Humidity Factor Method 2: Using Mr Retarder Mild
This method works particularly well with Mr Color 182 (flat coat) and Mr Retarder Mild (retarder). Simply prepare 182 for airbrushing as usual, and add a few drops of retarder to the solution. Spray a thin layer should do the trick, and you should see any blushing gradually disappear while it is drying.
Now take a look at the result using Method 2 in this delightful picture:
I developed Method 2 not only to fix blushing, but it also prevent the very issue from happening.
NOTE: As much as I want to brat about Method 2 being the perfect solutions, it is not. If in doubt, then for the love of Gunpla, FLAT COAT AT ANOTHER TIME.
[original posted: 2015.02.22]
[2nd version: 2016.11.23]
[this version: 2018.12.02]
[2nd version: 2016.11.23]
[this version: 2018.12.02]