“Roof coating (at 5-mil thickness):
K-value of 0.454, R-value 22”
“Surpasses R-19 heat gain testing”
There are coating manufacturers who claim that their ceramic microsphere or hollow glass sphere modified roof and wall coating/ paint can “insulate” a roof or wall. In some cases, the manufacturer actually assigns an “R-value” or “K-value” to their product. Some coating manufacturers go as far as to tout the ceramic material they use as “the same ceramics used by NASA on the Space Shuttle” and even use the image of the Space Shuttle in their literature. How can they make the claim of an “R-value” or “K-value”, it is simple…
The manufacturer will expose two samples to a heat lamp. One of the samples is coated with their ceramic modified coating/ paint, the other sample is not. After a period of time, a heat reading is taken from the back of both samples. Invariably the coated sample shows a lower heat gain than the non-coated sample. Here’s where they make their claim… The question is then asked, how much insulation would be required to reduce the heat gain through the un-coated sample to register the heat reduction of the coated sample. The answer given is an assumption as to what the “R-value” or “K-value” is.
Ask yourself this question, “if ceramics are such good insulators, why is there a handle on a coffee cup?”
The answer, “they are not good heat insulators.”
One may argue, if there are not good heat insulators why are they used on the NASA Space Shuttle?
Ceramics are used on the shuttle because they absorb heat and evenly distribute it, not because they are a good insulator. What keeps the interior of the shuttle from becoming an oven during reentry is a blanket made of Nomex fibers between ceramic tile and the interior of the shuttle. The Nomex fibered blanket is the actual insulation, not the ceramic tiles. This was never more apparent than with the Columbia shuttle disaster.
When Columbia shuttle lifted off, a piece of foam from the external fuel tank broke off and damaged a protective ceramic tile on the leading edge of the left wing. When the shuttle reentered Earth’s atmosphere the heat was not evenly distributed over the ceramic tile surface of the shuttle. This heat imbalance caused reentry plasma (super heated gas) to penetrate the protective ceramic tile and caused the explosion.
When it comes to roofing, the darker the surfaces color the more resistance to solar radiation, the more the resistance the greater the heat gain. The only “magic” in an energy efficient “cool roof” coating/ paint is the color, period! A white colored surface reflects maximum amount of solar radiation, second to a gold mirror.
What makes a roof coating/ paint different from a standard latex paint is the resin. Elastomeric resins are designed to be extremely flexible. This flexibility is very important on a roof because the coating/ paint must expand and contract with the roof surface. If it did not expand and contract with the roof, it would crack and eventually peel off.
The only “magic” in an energy efficient “cool roof” coating/ paint is the color, period! A white surface reflects a very large amount of solar radiation. Ceramics offer very little if any insulative value.
Still not convinced? Here what the experts have to say:
Do ceramic modified roof and or wall coating offer any additional “insulative” value to a paint or coating?
Sr. Research Engineer
Oak Ridge National Laboratories
Consultant with Artek, Inc.
“A coatings thermal resistance is negligible.”
Dr. Ray Taylor
“In side-by-side tests of white coatings with and without ceramic beads, where the coatings were roller applied on smooth surfaces, we have not seen any significant differences in performance of the two types.”
Ceramic Coatings Installed on Federal Buildings at Tyndall Air Force Base