What's a good aluminum roof coating?

Ahh ya, forgot about emissivity - good thing I'm not a rocket surgeon :)

maybe we should try painting those electronics heat sinks with Snow Roof, might help 'em work even better somehow!?

yankee camper wrote:
I have a 1992 Coachman 5th wheel with an aluminum roof. It was not painted for the 1st 2 years I owned it. I too figured that "this thing is like a mirror" and would reflect most if not all the heat off the roof. Well the 3rd year I painted it white with elastomeric roof paint and the indoor temps in the summer went down a good 10 degrees. Not going to get into a physics debate or try to convince anyone of anything,just posting MY results for anyone interested.

Your results follow the laws, no physics agents will be interrogating you, lol.
I'll expand on emissivity: the radiant reflection is not the only factor in the thermal equation. The bare metal has good reflection but poor emissivity, it doesn't give up the collected heat fast. White paint has close to the same reflection but has excellent emissivity, it transfers heat back out fast, hence less heat build up. I noticed a 10f reduction in heat inside the cabin, too.

Now, will anyone explain to me why a black electronic heat sink transfers heat better than a brushed aluminum one?

I have a 1992 Coachman 5th wheel with an aluminum roof. It was not painted for the 1st 2 years I owned it. I too figured that "this thing is like a mirror" and would reflect most if not all the heat off the roof. Well the 3rd year I painted it white with elastomeric roof paint and the indoor temps in the summer went down a good 10 degrees. Not going to get into a physics debate or try to convince anyone of anything,just posting MY results for anyone interested.

GordonThree wrote:
I guess somehow that product has bent the laws of physics, and I stand corrected. I thought the 85%+ reflectivity of aluminum was pretty good, guess there's always something better!

No laws broken, thank goodness! There is also emissivity of the material to consider and flat white paint lends the surface excellent emissivity.

Results are tested here.

I guess somehow that product has bent the laws of physics, and I stand corrected. I thought the 85%+ reflectivity of aluminum was pretty good, guess there's always something better!

Snow Roof

Brings the benefits of our professional-grade elastomeric roof coatings to your mobile home or RV. Chase pesky leaks and shrink cooling costs in style.

High quality, 400% elastomeric roof coating, acrylic, white liquid
Used to waterproof and maintain Mobile Home and RV roofs
Reflects 85% of the sun's heat rays. Keeps mobile homes cool inside during the summer
Cures to form a highly elastic, long lasting, tough seamless membrane that outlasts other petroleum based and latex acrylic products
Renews, seals, protects and prolongs life of roof
Durable and flexible over wide range of temperatures, to resist cracking and peeling
Protects against damaging effects of the sun, wind, snow, rain and ice
Dramatically lowers roof and interior temperatures
Soap and water clean up, immediately after use

I used a cheap white latex elastomeric roof coating--Cool Seal, IIRC. It lowered the temps considerably in the Summer. If you're trying to paint clean, polished aluminum, I'd suggest to use an antioxidant or etching primer.
FYI, these roof coatings will not seal the roof to protect against water leakage.

Aluminum is one of the best reflectors there is, see here:

I have know idea how many trailers you have had with aluminum roofs but I can tell you I have had a slew of them,infact, my current RV is the very first not to have it.They get hot,I mean really hot unlike the mobile home coating I used for 20 years.Aluminum trailers with aluminum roofs and siding are ovens in the sun.The roof coating reduces that.

When working I had to park in the sun at the shop for free rent and we had to hose down the roof and siding for it to even be livable and by adding the roof coating,it was much much better besides protecting the seams.

Actual experience with and without!

What's the thought behind "protecting" aluminum?

The natural oxide that forms on aluminum is pretty good, it's self healing and non porous (blocks oxygen and water) - unlike a paint or some other membrane that could hold water (and oxygen) close to the metal.

For keeping the insides cool, paint is working against you. Aluminum is one of the best reflectors there is, see here:

http://en.wikipedia.org/wiki/Reflectivity

White paint looks "brighter" to the eye because chemicals in the paint convert blue and violet light into yellow-green light, but it's actually absorbing more sunlight than bare aluminum, and that means more heat.

I use Snow Roof on my '70's trailers as well as on my Lance Pickup camper I had.It's a Mobile Home coating that works well on RV's.White and reflective keeping the inside cooler in the heat.