Paint temperature test.

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pictsidhe

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Joined
Jul 15, 2014
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7,531
Location
North Carolina
I want to paint my plastic aircraft project in dark colours. I am concerned about it wilting in summer sun. I recently came across Sherwin Williams 'Vinylsafe' paint. It is designed to be safe on vinyl siding. It is exterior Sherwin Williams latex paint tinted with only certain pigments. Pigments that don't absorb as much light energy as others. Benjamin Moore also markets an equivalent paint. BM told me that siding paint needs to have a LRV (light reflectance value) of 55% or above. Or, be cunningly tinted.

Last week, I bought two cans of Vinylsafe paint in SW3770 and SW9177. Those are the closest Sherwin Williams matches that www.easyrgb.com found to BS381C 241 RAF dark green and BS381C 105 Oxford Blue. The blue is for the roundels and it probably the darkest paint I will use on Coroplast other than serial numbers. Both paints are slightly lighter than the BS ones. Oh well. The LRV of the SW3770 is 8, that of SW9177, 5.

Today I have been painting a political sign for long term testing and 5"x5" pieces of flashing for temperature testing.
So far:
SW3770 'vinylsafe' in Sherwin Williams 'Emerald' exterior acrylic Latex. This looked like it would give best coverage.
SW3770 Sherwin Williams HGTV interior latex sample.
SW9177 'Vinylsafe' in Sherwin Williams 'Resilience' Exterior acrylic latex. This is the only exterior Sherwin paint available in quarts. I don't want to be buying trim paint by the gallon
SW9177 HGTV interior sample
White Valspar 'stormcoat' acrylic exterior latex. I had a tin.
Black Rust-Oleum 'High heat' rattle can paint. I had a can.

I wasn't going to start a thread here until I actually test and get results in a few weeks. But, I thought others may be interested in sending me coupons to include in my test. If you want to include something in the test, paint a 5"x5" piece of flashing or thin aluminium and mail it to me. PM me for my address.

As you can see from the image below, we can only see less than half of the sunshine that reaches us. Pigments that reflect invisible portions are going to be cooler than ones that absorb it. When testing a CCTV camera with infrared illumination, I was a little surprised to find that by far the lightest thing in the picture was my black fleece jacket!

 

FritzW

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Log Member
Joined
Jan 30, 2011
Messages
3,896
Location
Las Cruces, NM
Interesting stuff. I haven't finished my coffee yet so I can be forgiven if I missed the obvious point of the test...

Are you testing how much heat (IR) is reflected vs. how much is absorbed per type of paint?
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
7,531
Location
North Carolina
I'll be testing how warm my test coupons get in bright sunshine. Since I have two types of paint of the same colour, it will be measure of the absorbtion/reflection of invisible radiation between them. My test gear amounts to thermometers and thermocouples rather than a spectrograph, so it'll be an indirect measurement. But that's fine for our purposes. A quick preliminary test today with some cloud and a breeze shows the Vinylsafe does run cooler than the regular paint. I'll wait for a clear and windless day to test properly. I'll put them on a scale between Valspar white and Rust-Oleum black. Unless I come across other whites and blacks that are more extreme in temperature.
 
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