Just finished re-assembling the engine in garage last week. The engine had no rust before, but I ground off all the black paint to repaint the block cast-iron gray. Ground down to shiny metal, wiped clean & dry with brake cleaner and then several coats of paint--2 cans of Plasti-kote spray paint on the block. That was 3 weeks ago.

It has been raining every day this past week..humidity close to 80%. I opened the garage door yesterday during a downpour and it immediately turned all my polished aluminum parts in the garage foggy white, so I quickly closed the door and opened the door into the house to air out the garage.

Today I went to look at the engine and was shocked to see the engine block all freckled with rust spots right through the fresh paint because of yesterday. I couldn't beleive it. How could this happen so fast, through the new paint, sitting in a garage, all in 12 hours? My nice new painted engine now looks like crap.

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1973 RS Z28: Littlefield race series 6-71 supercharger on a 355 w/ AFR 195 heads, 12-14 lbs boost, 7.6:1 static compression, CompCams hydraulic roller (276/288 advertised, 224/236 @.050 duration, .510/.527 lift w/ 1.52 rockers on a 113 lobe separation), AFR Hydra-Rev kit, Eagle 4340 Forged Steel crankshaft, ARP studded bottom end, Eagle ESP H-beam rods, TRW forged reverse dome pistons, Comp Pro-Magnum 1.52 roller rockers with 7/16 studs, twin 750 Edelbrock carbs, 1&3/4 inch Hooker Super Comps, 3" dual exhaust with cross over pipe. MSD 6AL ignition & Pro-billet distributor, Tremec TKO-500 5-speed, Moser 12 bolt with Eaton posi, 33 spline axles & 3.42 gears.

Was the block hot tanked? If so I have never seen a problem like that.

Yes it was hot-tanked before it was painted the first time..engine is being rebuilt just 800 miles later.

I have never seen anything like this either..and not so happy that I might have to disassemble the engine a bit to re-paint it right, but dont want it to happen again

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1973 RS Z28: Littlefield race series 6-71 supercharger on a 355 w/ AFR 195 heads, 12-14 lbs boost, 7.6:1 static compression, CompCams hydraulic roller (276/288 advertised, 224/236 @.050 duration, .510/.527 lift w/ 1.52 rockers on a 113 lobe separation), AFR Hydra-Rev kit, Eagle 4340 Forged Steel crankshaft, ARP studded bottom end, Eagle ESP H-beam rods, TRW forged reverse dome pistons, Comp Pro-Magnum 1.52 roller rockers with 7/16 studs, twin 750 Edelbrock carbs, 1&3/4 inch Hooker Super Comps, 3" dual exhaust with cross over pipe. MSD 6AL ignition & Pro-billet distributor, Tremec TKO-500 5-speed, Moser 12 bolt with Eaton posi, 33 spline axles & 3.42 gears.

Perhaps more than one issue: A) if it was extremely humid when you cleaned the block initially to paint it- corrosion may have started before any paint was put down (not visible brown rust- but the start of oxidation), and B) your plasti-kote paint may be worthless- it wasn't a primer of some-sort was it? Primer will absorb moisture and suck it straight through to the metal underneath.

Did you paint with high humidity? If so that could be part of the cause, dry air is your friend, Im willing to bet water got under the paint before it even dried. My fahter inlaw does autobody painting and when its raining outside or the humidity is higher then normal it takes many more hours for a painted car to dry, even with heat lamps going 100%.

It must suck where you are, I was once in Chicago during the summer and it was so humid that I swore I saw water just floating in the air and that is why I live in CA, 50% humidity is considered high here. 80% and I would probably die.

Edit: Just re-read your first post, I noticed that you said you ground down to shiney metal, read the back of the paint can, most paints need a certian amount of ruff-ness to beable to provide a good seal. The paint actually needs something to grab hold of and smooth shiney surfaces are very poor surfaces for paint to adhear to. Primers provide this ruff surface for auto paints (steel bodys are smooth) where as a primer is like a sponge and that lets the paint grab hold. A cast piece like an engine block is already ruff enough so primer is not required unless of course you smooth it out.

[This message has been edited by Joekool (edited June 13, 2005).]

You need primer on the block first then the
top coat and then the clear to seal it all up.

A read through past posts on painting blocks and most said that primer is not necessary on engine blocks and I do not think it is common to put clear over the paint on engine block, so I do not think that is the problem.

Ugly is better. Trust me. How many pretty engines make mind-bending power? None of mine ever do. My engines look like partially rusty old frankensteins by the time they're really belting out serious levels of power.

But I don't recall ever having block paint rust through in 3 weeks and one rainstorm. And I paint with a rattle-can (high temp gloss black engine enamel from Pep Boys) and no real effort to prep it, either. That's odd.

I have painted a few blocks and heads, and have never used primer or clearcoat. I just think plasti-cote is not that good of a paint. I think I used the other cheap stuff, dupli-color or something like that.

This block has never been wet..never been out of garage...it was the humidity. paint must be too porous.

Ugly or beautiful is not related to power. I have the power, so I will make it beautiful, too. It certainly wont slow the car down.

I just read an engine building book and they say to never use a primer on the engine block or heads because it will just burn off.

I noticed the rust spots will wipe off with a damp rag, which I will immediately dry. My game plan is I will remove the front blower pulleys and tape everything off, then paint again really heavy this time and then use a high-temp clear coat (which I didn't use the first time because it darkens the color).

A couple weeks a go another user on this site gave me a great tip. He told me that Vermelion orange, 1 shot, sign painters paint was was a near perfect match to chevy orange. You can get this stuff from Eastwood or any automotive paint supply store. I recently bought some myself, and the hardener, and painted all of my cast iron parts with a foam brush from home depot and it looks great. It was a very cool and dry night here in AZ when I painted; about 80 degrees F and 5% humidity. Good luck

Greeny, I am the guy that turned you on to the Eastwood Vermillion orange. I'm glad it worked out for you. I love the way mine turned out. You can see it on my web page and by going to specs. I would highly recommend this stuff to anyone wanting to dress up without tearing down all the way.