A test of wood surface temperatures related to paint
NOTE: This is not research quality experiment, but a simple test to point me towards others tests and experiments. IR thermometers have limited resolution and are subject to calibration errors. The real experiment is being conducted on 3 identical Stevenson Screens with an NIST calibrated data logger and the results will be published in a couple of months.
You may recall a blog entry where I talked about
Bad Paint Job = Rising Surface Temperatures? The premise is that the early
weather station temperature shelters called Stevenson Screens originally have
been specified to be painted with whitewash when the were designed and
comissioned in the 1890’s
|Stevenson Screen at the NWS office in Monterey – good
paint but right next to asphalt parking lot and concrete walk – a
Lately they have been repainted with lead, oil, and
latex based paints which have significantly different infra-red properties
(Pigment: Titanium Dioxide) than the Calcium Carbonbate based whitewash.
Curious to follow where the evidence leads, I decided to do a test today.
Preliminary spot test of the temperatures of bare wood, latex paint, and
lime based whitewash (CACO3)
5/17/06 by Anthony Watts, Chico, CA
Click thumbnail pictures for larger ones
Test setup in full sun. Three slats of 1×4 pine, 2 feet long each, bare wood
in the center as a control, latex on the left, whitewash on the right.
Methodology: Whitewash was mixed after conferring with Chemist Richard
Godbey of the Chemical Lime Company in Henderson NV and after reading a paper he
authored on the history and home creation of whitewash which you can read here
Pictures: Materials, Mixing Whitewash, applying whitewash coat
1, coat 4 after 24 hour curing
Slats were all cut from same plank, chosen to be as knot free as possible,
cut to exact same size, 2 ‘ long, and spaced equidistant on the frame.
Measurements were taken 3 times with IR thermometer shown below, at1:50 PM,
2:10PM, and 2:20 PM PST to be sure results were repeatable. What you see below
is the 2:20PM spot test.
Device used to measure surface Temperature, A Fluke model 561 HVAC Pro IR
thermometer, handheld with laser dot sighting of measurement target
Temperature of bare wood, this represented average of several scans. The
temperature was 102.6 degrees F
Temperature of Latex Painted wood, the leftmost slat temperature 88.2F
Temperature of Whitewashed wood, the rightmost slat temperature 82.5F
Temperature difference between bare wood and Latex painted wood was about 14
Temperature difference between bare wood and whitewash painted wood was 20
Temperature difference between latex painted wood and whitewash painted wood
was 5 degrees F
Next Test: time series temperature over several days measured by NIST
calibrated data logging thermometers compared to ambient aspirated air