BS: acrylic enamel paint

Subject: BS: acrylic enamel paint
From: GUEST,J
Date: 29 Oct 05 - 01:23 PM

What, if any is the difference between acrylic enamel house or auto paint? Just painted my truck and want to paint the cap, bumpers and trim a different color than they are now. Am thinking of using acrylic enamel satin black with enough reducer and thinner to make it the right consistancy for the sprayer. Indoor/outdoor house paint is MUCH cheaper than auto paint. Anyone have experience trying something like this? Thank you!

Subject: RE: BS: acrylic enamel paint
From: John MacKenzie
Date: 29 Oct 05 - 02:42 PM

Auto paint has longer polymers as the body work etc flexes in use, they also contain stabilisers to deal with the fading effects of sunlight, and road salt etc.Even Hammerite is too brittle and will chip off mudguards etc when hit by grit etc thrown up from the road.
Giok

Subject: RE: BS: acrylic enamel paint
From: JohnInKansas
Date: 29 Oct 05 - 02:48 PM

J -

Out here in "Billy Bob" land we probably have seen just about everything there is used for auto paint. Unfortunately they don't drive around with labels to tell you which fender/door is what paint.

Original "factory" automotive finishes generally require baking at relatively high temperatures, to fuse the enamel.

Since the ham sandwich the kid left under the seat, and a few other things that might have once been functional parts, don't stand baking very well, and automotive sized ovens aren't cheap, aftermarket paints have to rely on chemical cross-linking to get the hardness and gloss expected on autos.

At least some of the common re-do automotive paints require addition of catalysts to complete the mix, either immediately before or during the actual process of spraying. This allows a pretty good simulation of the factory baked enamel finishes.

Other automotive paints have all the ingredients, but a volatile "inhibitor" is mixed in to prevent the hardening chemistry from proceeding until the inhibitor evaporates during drying. (A bit like cyanoacrylate super-glue.)

While some acrylic and latex-acrylic house paints are similar to this last kind, the automotive enamels are expected to be used on non-porous surfaces, and form a non-permeable layer. The principal use of house paints is on porous and permeable surfaces, and they're usually meant to remain at least partially permeable to moisture. (The permeability helps to keep the wood from warping.) While some of them work pretty well on metal/plastic non-permeable materials, in general they don't adhere quite as well as the automotive kinds.

Either kind of the "inhibited cure" materials usually has pretty restrictive mixing/dilution limits, so you'd need to read the can carefully.

If you only want very basic colors, you might see if your local farm supply has some "implement enamel." Tractor Supply Co. in my area stocks it in Black, "John-Deere Green," and "Allis Chalmers Orange," at least. This is the old-fashioned solvent based enamel that they used to use before the fancy chemical-cure stuff became popular.

I still occasionally see small cans of RustOleum brand solvent based enamel, and it may be available in bulk quantities by special order, but they've gone largely to a water (latex or latex-acrylic) formulation due to emissions regulations, and most of that is sold in aerosol cans. The older solvent based stuff used to be the "enamel of choice" for metals when good "sticking" and protection was needed; and I have known vehicles (or multiple parts of them) to be painted with it. It seemed quite durable at least.

As Giok notes, a substitute material probably will have lesser performance than a "real automotive" enamel; but if you really need to do it cheaper, one might be cheaper (at least long enough to decide what colors to use when you re-paint).

John

Subject: RE: BS: acrylic enamel paint
From: GUEST,J
Date: 29 Oct 05 - 03:10 PM

JohninKansas and Giok,

Thank you for your informed responses. Called around to some DIY friends and have been encouraged to NOT use housepaint for the reasons both of you have pointed out. Medium grade acrylic enamel auto paint is around $75.00 per gallon. Tried to do it on the cheap...backyard style. I'll be on my way to the auto-paint store when I log off. Thanks again.

Subject: RE: BS: acrylic enamel paint
From: GUEST,mack/misophist
Date: 29 Oct 05 - 09:16 PM

Many still think the old fashioned automotive laquer was the best ever. Unfortunately, it needed nitro cellulose. When the last plant in the US (Hercules Powder Co; Hercules, Cal) decided nitro was too dangerous to continue producing, automotive laquer was no longer made.

Subject: RE: BS: acrylic enamel paint
From: JohnInKansas
Date: 30 Oct 05 - 01:49 AM

The automotive industry doesn't even call it paint or enamel. Now its "a vehicle coating system."

Most automakers now claim to use multi-layer finishes, but they're secretive about how they're actually put on. Often there's a "subcoat" that is basically a surface preparation to make the rest of the stuff stick, followed perhaps by a "primer coat" (strangely sometimes still called that) that's supposed to provide a "barrier corrosion protection," maybe followed by a "sub-coatin" to provide adhesion to the anticorrosion layer, then an "undercoat" that often appears to do little except set a neutral color, then a "color coat" of course, followed by one or more layers of "clearcoat" to make everything shiny. Some claim a "hardcoat" between color and clearcoat.

In Automotive Engineering magazine (SAE International) one maker not too long ago was claiming a "17 layer finish" but I think they must have been counting the "do-overs."

John

Subject: RE: BS: acrylic enamel paint
From: John MacKenzie
Date: 30 Oct 05 - 06:37 PM

I did hear that VW put a negative charge into the body shell, and a positive charge into the paint, when they painted their cars. In theory all they have to do is fill the spray booth with a fine mist of paint and magnetism does the rest.
G..

Subject: RE: BS: acrylic enamel paint
From: GUEST,J
Date: 30 Oct 05 - 07:53 PM

G,
Our teacher showed us a film in 7th grade shop class about VW Beetles. The paint was magnetized. The bodies and parts were dipped and allowed to drip dry then baked. I remember being very impressed.

Subject: RE: BS: acrylic enamel paint
From: The Fooles Troupe
Date: 30 Oct 05 - 08:32 PM

It's not magnetism, it's static electricity!

Subject: RE: BS: acrylic enamel paint
From: Bobert
Date: 30 Oct 05 - 08:56 PM

Firget acrylic paints fir cars....

Use Centuri enamal (oil based) and put in a little hardner and it's gonna be just fine...

Water based paints and cars don't mix...

Bobert

Subject: RE: BS: acrylic enamel paint
From: JohnInKansas
Date: 30 Oct 05 - 09:24 PM

Bobert - not all acrylics are water based, although most of the ones you'll find at the hardware store are.


The main reason for using the static charge method isn't really to improve the paint job. It's to minimize the amount of paint that gets suspended and dries out in the air. The "static" method not only minimizes the amount of air filtering needed to meet workplace air quality rules, it can, if properly used, give a very substantial reduction in the amount of paint sprayed to get a given amount of it stuck to the car.

It's also a lot safer for people working on the paint line, although that's maybe secondary to the $$$$$$ saved on paint. And almost everybody in the industry does it now, not just VW.

They looked at it in the aircraft business a while back, but when you put enough voltage on something as large as most airplanes it becomes sort of a hazard to anyone working in the area; and most aircraft painting is still "hand sprayed." No big conveyer systems and robot nozzles.

There's a fair amount of "powder coating" done as well, although not so far as I know on complete body assemblies. Heat the part, and dip it in powder or blow powder agin' it, and the powder melts and sticks where it hits something hot. Even when sprayed, what doesn't hit something hot enough to stick can be swept up and used again, so it's a "low loss" process - sort of.

With solvent based sprays, once it comes out of the spray nozzle it's used up, whether it goes where you want it or somewhere else. There's some "recovery" to keep the air semi-clean, but what's recovered usually isn't very useful.

John