Combination of coverage, dry time, finish and durability.

Except for dry time, Mercury Marine Phantom Black is pretty good, probably about $15-20 a can. I painted an aluminum small outboard propellor with it and it stayed on well. Also impressive is a some silver PleasureCraft Marine engine paint made by Krylon I think.

I've been spraying old truck parts with Rustoleum and Krylon gloss black, the Rustoleum probably covers better, but is slow drying.

What is different about a paint that takes hours to dry vs one that is dry to touch in minutes?

Is primer really a magical super adhesion base coat, or really comparable to using two layers of finish coating paint?

Primer basically has one purpose. To stick to something, as well as other properties, rust prevention, galvanizing, etc, so different blends of polymers are used

Spray paint on its own is designed to be a decorative protective coating primarily.

Dry time is connected with what attributes the product has. Probably find higher sheen products take longer to dry so the flow and leveling has time for a smoother finish. Temperature and humidity also play a huge aspect in dry time. Time to full cure is a whole different aspect

You will definitely find the cheapest sprays sag easily, have more over spray, aren’t as high in pigments so it can take 3+ cans to accomplish what 1.5 will of a higher quality product

Depends on what you're doing.

Repainting faded garage door trim, painting plastic to prevent UV degradation, and other low dollar items just use Rustoleum from ACE or Big Box store. Been using Rustoleum 2x. They advertise as no primer needed but do sell a primer.

I bought a fairing for my motorcycle that arrives black, and needs to be painted to match. I put the same fairing on my old Honda, and on my current Indian. I grew up with a Dad in autobody and in my younger days bought cars that needed repainting so I helped him quite a bit. Felt like the fairing was within my skillset to prepare and paint. Colorrite nailed the paint color both times. Additionally, their primer, paint, and clear sprayed well for a spray can (good, but not great like Dad's HVLP professional spray gun). Colorrite sells a 3rd party adhesion promoter so I ended up spraying that first on the fairing, then their primer, then multiple layers of their color coat, and then multiple layers of their clear coat. My skills improved and the Indian came out even better than the Honda. I don't know if the specific adhesion promoter was needed for the fairing or if their primer was sufficient, but my first car had one of the first plastic bumpers and remembered Dad using an adhesion promoter on it.

At work, I've spent quite a bit of my career with carbon steel equipment in a corrosive environment (e.g. Gulf Coast TX & LA, or offshore). Getting the steel to a near white preparation and then properly applying a zinc-rich primer is the key to longevity. We tend to do a multi-layer paint system over the primer to further increase the longevity. There is a fire and explosion risk to repaint in the future so it's best to do a great job at original construction when there are no hydrocarbons present.

quote:

Originally posted by pbslinger:
Combination of coverage, dry time, finish and durability.

Except for dry time, Mercury Marine Phantom Black is pretty good, probably about $15-20 a can. I painted an aluminum small outboard propellor with it and it stayed on well. Also impressive is a some silver PleasureCraft Marine engine paint made by Krylon I think.

I've been spraying old truck parts with Rustoleum and Krylon gloss black, the Rustoleum probably covers better, but is slow drying.

What is different about a paint that takes hours to dry vs one that is dry to touch in minutes?

This mostly (but not always) has to do with the resin system, for the most part, these types of coatings fall into four categories of alkyd resin, Chain-Stopped, Short-Oil, Medium-Oil and Long-Oil alkyd resins. The "chain, short, medium and long" oil refers to the polyol molecule chain, to simplify, the longer the chain, the longer the dry time, but also the better the performance. Chain-stopped alkyds are usually seen in the cheap aerosol or bulk enamels you find at Wally World, or the big box hardware chains, they dry quick and have good color and gloss, but will oxidize quickly when exposed outside. You typically don't see any of the other, longer-chain alkyd resin based coatings in large retail (Krylon, Rustoleum, etc.), you see these in lesser-known coatings manufactured by smaller paint grinders (think POR-15 or Zero Rust).


Is primer really a magical super adhesion base coat, or really comparable to using two layers of finish coating paint?

A primer is desinged to do a few things, establish a level surface for successive coats, create a uniform base color to aid in color development of successive coats and provide a level of corrosion protection. Some primers do more (adhesion promotion as an example), some do less, but these properties are the most typipcal. Are primers necessary? That depends on your definition of a "good paint job", if you are just painting a wheel barrow, then no, primer is probably not needed but if you are working on a street rod, then taking the extra steps ensures a finished appearance that gives you the look you need.

I'm no chemist, but I've been in the paint business 30+ years and have picked up a few things along the way.....

My preference for primer is SEM.

https://semproducts.com/products/refinish/primers

The topcoat preference varies with the task requirements.

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Originally posted by tatortodd:

Depends on what you're doing.

quote:

Spray paint on its own is designed to be a decorative protective coating primarily.

I built a catwalk for my boathouse from angle iron about 35 years ago and painted it with $1 a can WalMart spray cans. Black over red primer. Some of the black is gone showing the primer, but no rust on it. Thats impressive performance in a wet outdoors environment.

W0w-learning a few things here - thanks. Cheers!