Painting plywood black -- too hot?

[kimballa]

Hi all, I'm building my first art project for the burn and could use some advice from veterans here.

The art is LED-based and will only operate at night (so operating temperatures aren't an issue). However, it needs to survive the days before it can hit showtime all week. The LED systems will be mounted on a plywood board like a billboard. Having tested different options, the lighting system looks better if the background is painted black vs left as bare wood, so I'd like to do that if I can.

I'm a bit concerned though; will the whole thing get much hotter in the daytime if painted black? And if so, how much?

I found a study that suggested that the roofs of cars (which are metal and conduct heat better than wood) would get up to 20 degrees hotter in Sacramento if black vs white. 20 degrees, I think the electronics (and acrylic plastic housings on the lighting) could handle. Much more than that (~35--40 degrees) and I think the acrylic might start to deform.

Most wooden structures I've seen are unpainted -- but I don't know whether that was because of effort/cost, aesthetic discretion, or thermal concerns.

• How hot does plywood get in the day vs. the ambient air temperature?

• Would black paint raise that, and does anyone know by how much?

(Related, does paint lead to moop issues greater than general moop risks related to bare plywood? Would a coat of varnish mitigate that, or just make it worse?)

[kimballa]

If folks do have playa-specific wisdom to add I would definitely appreciate it.

That said, today I was able to find some academic literature on the subject of temperature ranges experienced by wood as used in home construction though, which is helpful. Passing it on here in case others find it useful:

"Study of temperature in wood parts of houses throughout the united states" (https://www.fpl.fs.fed.us/documnts/fplrn/fplrn012.pdf) describes max temperatures (by month) reached by various parts of walls and ceilings in homes in six cities across the US, including one in Tucson AZ and another one in Texas. The max wall temperature was ~130 F and max rooftop temperature was ~170 F.

"Temperature histories of plywood roof sheathing and roof rafters as used in North American light-framed construction" (https://www.fpl.fs.fed.us/documnts/pdf2002/winan02b.pdf) further concludes, "Black-shingled roof systems tended to be 5° to 10°C warmer on sunny afternoons than did white-shingled systems" -- so regardless of whether a house in Tucson gets as hot as plywood on the playa, I think this means the temperature difference between dark paint / unpainted is going to be roughly 5--10 C. I think that's unlikely to be the deciding factor in whether the acrylic plastic on my project melts...

[Skuzzy61]

I'll toss this out there. Most acrylic plastics have a deformation temperature of around 200F. There are a few variables involved which can alter that, such as the load on the acrylic, the thickness, any finish on it, and so on.

[HarryN]

Part of the reason that some structures are unpainted might be that some get burned and paint isn't a good mix for that arrangement.

It is pretty easy to test a piece of wood painted black. Just buy a quart and paint it on.

I have stained some wood black for some home projects and the difference in my yard on a hot day was that the plywood without stain I could touch and the stuff with black stain I could not. Not exactly an engineering answer but maybe useful.

I have been fairly unimpressed with the black paint that I could buy (scratched easily) vs the stain seemed to mostly soak in. The stain we can buy locally seems to never completely cure - but it is easy to touch up.

[Jordancc]

The dust will turn all black surfaces a medium gray color within a day or two.