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Comment by sandworm101 | Hacker News Reader

This is nothing new. You are just now hearing more about it because of how journalism is being done online. There have always been lots of revolutionary things happening in labs. They are rarely ever practical, or if they are it will take decades to bring to market. How many dozens of new battery techs are announced as being "better than lithium ion" only to disappear once everyone realized how impractical they are. Such announcements were once confined to scientific journals and trade mags. Now the great algorithm makes them daily news bulletins right beside the Kardashian latest puppy video.

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Your point clearly has merit in many cases, but paint seems almost the epitome of practicality. Assuming that it could be mass producible at a price similar to premium house paints I can't see the problem in bringing this to market.

And from the article: > In the US, New York has recently coated more than 10 million sq ft of rooftops white. The state of California has already updated building codes to promote cool roofs.

> Assuming that it could be mass producible at a price similar to premium house paints I can't see the problem in bringing this to market.

Unfortunately, that's the whole point of this little discussion, right? GP is saying how many things like this, yes, seem like they have merit, but at the end of the day can't be produced practically outside of a lab.

There are a lot of practicality/implementation concerns to paint other than what color it is. Just as many if not more than there are for battery technologies.

Does the paint stick to the surface you want to paint, how is it applied, what is the coverage, is it durable, does it repel contaminants, can it withstand the environmental conditions, is it chemically compatible with the surface, it is chemically a concern for the other items/humans/animals that may come in contact with, can it be produced at scale, does it (and it's vehicle for application) meet regulatory standards? etc...

They used standard acrylic paint manufacture techniques, just substituting barium sulfate for the usually-used white pigment titanium dioxide. So most such questions should be answered simply by looking at previous experience with existing white acrylic paint.

So, in about 10 years we're going to have yet another source of trillions of particles of microplastic?

Titanium dioxide and barium sulfate is not plastic. They are anorganic compounds.

The other ingredient of acrylic paint is an acrylic polymer.

That will not increase plastic in the environment unless the new paint is less durable or incentivizes painting previously unpainted surfaces.

Other factors include how it ages, w.r.t. thermal emittance (emissivity) and solar reflectance (SRI). See the "3 years" columns here: https://coolroofs.org/directory

Many products drop by several % after a few years.

one thing i’ve learned from doing little home improvement projects over the past few years is that paint is a 2-part product, primer and topcoat, and neither should be skipped if you want good results. generally speaking, primer sticks and seals while topcoat colors and protects. this isn’t made obvious in any way to the novice, and big box store workers seem as ignorant about it as anyone.

Depending on the application, the primer coats can fulfill a couple other requirements as well:

If you want a really smooth topcoat, you usually want to sand past what you can reasonably/economically/effectively do on the substrate. Some primers are formulated to sand nicely to a powder (as opposed to balling up in clumps on the paper). You'll see this spraying higher quality paint grade work. You have to have a decent surface before you prime, but the primer can really smooth it out for the topcoat.

If you're finishing pine with knots in it, you'll want a primer that will seal the knots, otherwise the pitch will eventually bleed through and discolor the topcoat. Shellac excels at this.

Shellac is also outstanding as a sanding sealer. You can use that in a couple of ways: to fill the pores in the wood so they don't get full of sanding dust (which can be key if you have inlay of strongly contrasting woods), or to stiffen the fibers of softer woods so you can get a better/smoother sanded surface for the next steps in the finishing schedule.

Shellac is also often used as a barrier coat between otherwise incompatible finishes or when you have a relatively fragile stain layer. If you're putting an oil based finish over an oil based stain, you run the risk of picking up the stain as you apply the topcoat, especially if you're brushing or wiping the topcoat. Because the solvent in shellac is alcohol, you can pretty freely brush it over oil or water based stains without risking a disaster.

And yes, I do use primers other than shellac from time to time if I have a specific need, but dewaxed shellac is compatible with basically everything, so I always have a can around.

N.B. I'm not a professional finisher. Don't take my word on any of this; test your prep and finishing schedule on scrap!

> “If you're finishing pine with knots in it, you'll want a primer that will seal the knots, otherwise the pitch will eventually bleed through and discolor the topcoat. Shellac excels at this.”

yes, i learned this the hard way, albeit on a simple set of wall shelves as cat stairs that i can easily fix eventually with shellac and another topcoat (when i get around to it).

And that's just for home improvement store paint. More sophisticated painting processes, like for automobiles, can be 5+ different types of coatings.

i.e. electroplate > primer > base > mid pearl > clear

The big box stores employees at the paint counter seem as ignorant as a novice about the vagaries of application most likely because they themselves are novices. They may know quite a bit about colors and matching and how to work the mixing machines, but they probably don't have much more experience painting than the average homeowner. That knowledge comes more from doing, whether its a handful of projects as a homeowner, or regularly as a professional.

IMO, the stores could do better about offering basic information about this, about when one would need a primer, or just a topcoat, what kinds of paint bases are appropriate for what applications, what kinds of application methods are appropriate, etc. Instead, the response of the big box stores seems to be to skip the question entirely with combined products, e.g. "paint and primer in one".

yes, there's no experience or incentive for better knowledge in big box stores unfortunately. i've moved on to buying from a local paint specialty store, which is owned by a family that i believe is/was in the construction/painting business. they cater mainly to contractors but also sell to the wider public.

oh, and yeah, paint and primer in one does neither job very well.

As someone who's painted professionally, I can confirm the truth of this.

Yep, been there too: paint is really something where you want to avoid the big shop and goes to speciality stores instead (paint peeling from the wall? Color changing after a year? Done and done --> switched to a dedicated paint store == no more issues, the paint itself is more expensive sure but the result is stable)

Paint peeling could also be a humidity issue. I had paint peeling on my ceiling due to water problem in the basement.

Actually that last bit there seems to be more important to me than the actual tech here. So without this tech people are painting rooftops white. And I'm guessing that's already like a 90% reflectivity? -- So there's really nothing to wait for if you want to cool your house. Just buy... exterior white paint.

If you wanted to wait for this specific product, that's fine, but that's almost like waiting for 26% efficient solar panels instead of ~23% we already have (even though most production panels are 18% - 22%)...

And actually this is also one of those things that also helps beat Tesla Solar roof - get a white paint - THEN add bifacial solar panels. So the Tesla roof panels is actually worse for your overall cooling than regular panels now.

The whole point of the discussed paper and of their patent applications is that normal white paint is not good enough to cool something exposed to solar light.

The white-painted object will heat less than when painted in another color, but it will heat anyway.

The white paints described in the paper and in the patent applications, which use either barium sulfate or calcium carbonate instead of the normal titanium white pigment, actually cool the painted object, even in strong solar light.

oh yes, there was a sort of 3d memory lasered into scotch tape(german tesa) rolls. They just could not make it durable.

I researched this a few weeks ago and commented here[1]. I got a reply from someone with firsthand knowledge of the work. I love HN for that kind of stuff!

[1] https://news.ycombinator.com/item?id=26040009

I understand that there are scientific discoveries which are worth the investment money or otherwise. But I would prefer the great algo to pick these up for me rather than which star admires who.

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