General Tech Questions About Painting

Can I be reasonably comfortable that using a good auto paint from a can on the shelf will result in a good paint job--assuming I prep correctly?

I'm only painting my engine compartment. For my primer, I'm using an etch primer because I've got lots of bare metal. My question, though is this: Why not always use an etch primer? If it adheres better, isn't that always better?

Finally, some of the existing paint that I must paint over (it's right where the bad stuff is) is a really good hard acrylic. Do I just buff it up a little bit with 320 before priming that area, too? I assume the etch primer will help adhere to the existing acrylic without taking that down to bare steel, correct? Otherwise, I'm really in for a lot work over not much--the problem is mainly the typical corrosion on the battery box, hydraulic plate, etc.

Thanks all.

I had the same questions a year or so ago on my MGB and I got mixed answers on the self etching primer. I'm lucky that I have a close relative who has a body shop and he advised me to go with a good quality primer vs the self etching since I had lots of good original paint. I used 320 grit to degloss and it came out looking good. One thing that I would not repeat is the enamel paint the paint supply co loaded in the spray cans...it's very sensitive to gas and other under bonnet contaminants, just not very durable. A body shop can mix a good quality 2 stage that will last a lot longer and I think I paid $40 for the paint, reducer, and clear coat (pint).
Rut

I'm just a shade tree painter but If I understand you question, you mean a can that you have on your shelf. If that's correct then it does have a shelf life, particularly if it's been opened. Considering how much work goes into painting, even just the engine compartment, I would use a fresh mix from the paint supplies.
I have, however, used old once opened paint, well strained, with little trouble but I think it's harder to get it reduced properly, and that of course affects the final finish.
Etching primer etches the metal and improves the bond between the primer and the metal. IMO, there is no need to prime well adhered paint, unless you are looking for a more uniform base, e.g. a surfacer coat.
Tom

I too, am a little confused by " can off the shelf "... If your talking about a rattle can like you get at the autoparts stores...like Duplicolor, you'll have trouble keeping it wet enough while you paint an entire engine compartment to get a even coat. As far as the etching primer: That is generally for use on bare metal surfaces in a very light coat to help the surfacing primer adhere,as Tom said. Different types of paint react differently to existing paint so it's best to use "same brand" products when painting. If you are going to use either a single stage or two stage system, you should prime the entire area to be painted with two part primer surfacer on a clean sanded surface, including over the existing paint. 320 would be fine. By "clean" I mean, using a degreaser to wipe down all the surface and nooks and crannies. Then scuff the primer. I used a single stage urethane paint on the engine bay from Dupont. I had it mixed to match the two stage finish color that is on the exterior. It requires three part mixing before use. (paint, reducer and hardener) And it requires a spray gun and compressor. A lot depends on what you are trying to accomplish and how near perfect you want the finished product to be and how far "torn down" you have the engine compartment. Hope this helps a little.

Sorry, I meant "off the shelf" by just buying a standard spray can at my local auto paint shop. It's Dupli-Color, and the top on the can is a virtual match to my car. I'm verifying that on a part I removed. However, the shop assures me that for painting an engine compartment it should look fine. The areas are: battery box, both flat platforms under TR4 hood (tool rest, hydraulic plat), around the bell housing folds, parts of the visible firewall around the battery box, and a little toward the wheel wells. Sounds like I should avoid getting etch primer overspray on the good paint base areas, and for those areas just buff the paint up a bit, keeping the primer to areas truly approaching bare metal.

Sounds like you're just interested in doing a clean up/touch up. I'd just use the duplicolor primer too then. If you have any openings in the area, tape them off so overspray doesn't get where you don't want it. Not sure how you will avoid getting overspray on things that aren't painted though, i.e. hoses, wires, fuse block,etc.

Are you supposed to wet sand between paint coats? My first coat in the engine compartment, using matched Dupli-Color after sanding and priming, and following the primer with 600 sandpaper, went on quite grainy and rough. I can't imagine putting a second coat on that. I realize the clear coat supposedly adds the gloss, but shouldn't I smooth down that first base paint coat?