Help…I can’t seem to paint my engine cover without it cracking

[TIE FIGHTR]

Originally Posted by caverman

The can says "No Primer Needed" right on the front. So...no....didn't primer it.

I've got to go get a hose clamp for my CAI so I'll look over in the paint section while I'm there and see what they have.

Pick up some 1000 and 2000 grit wet/dry sandpaper while your there...they're like $2.50 a pack...make sure it's the sandable plastic primer...that's how I did my bowties and they are slick and polishable.

[chef-beavis]

The key here is that the first time came out almost perfect. Dish soap will not cause problems if the part is rinsed well afterwards. What I suspect is happening is that most bomb cans are enamel. Enamel skins over but never really dries 100% thru. The can should give min and max time between coats. If you sand thru the skin and re-spray, you need to leave it dry for the max time again, at the least. I am fortunate enough to not have to mess with uncatalyzed paints than come in bomb cans but back in the day when we repaired cars painted with uncatalyzed enamels we had entire cars blow up like this. The only fix was to strip them.

Your best bet is to strip it and respray, doing all desired coats in one application while sticking to the recoat times on the can.

Good luck!

[johncaye]

Looks like an adhesion or cohesion problem. The thicker it gets, the worse it gets? Did you try to take it all off and start fresh? A light sanding and then cleaning with a denatured alchohol. Where are you paint guys?

[vuduman67]

Chef beavis is right on the money on this one. The soap is not the problem although it is definatly not a good idea for painting anything. What your are experiencing is a reaction with the paint itself. Spray cans do not normally contain a catalyst for hardening. Basically they rely on air to cure. When you atempted to refinish a second time the fresh paint created a chemical reaction and lifted and curdled the first paint. You have two choices to fix A:your best choice and also a big pain in the butt is to remove all the paint and start over, or B: sand the surface smooth and apply a water base primer which will create a barrier between the old and new paint. Once you have the primer on and dry sand it smooth and apply the new paint in light coats. Do not sand through on the primer anywhere though, if any of that old paint is exposed it could lift that area again.
Good Luck!
Ps: A new cover is only $85.92 list so if it turns out it is not salvagable there not to expensive to replace.

[Rcamaro]

Ahh I know what you did. I did this back in highschool painting my valve covers on my maro before. FIrst off your friend is right you probably should have sanded it lightly with a scotchbright pad first, but thats not why the paint is reacting, that has to do with adhesion. Spray your base and read the label to see the that you apply the clearcoat within the right time frame it states on the can. There are too timeframes you need to know about when shooting clear. You have the time to spray clear right after the base so it bonds together ( granted you have a base and clear that are supposed to be used together like this) and you have the time frame of waiting till the base coat fully cures and then going back and lightly sanding the base and applying the clear. Those specific time frames and temps are on the back of the spray can. Read the directions on the can when spraying and follow them and you will have better results like Chef-beavis and vuduman67 also stated.

good luck with it, its good to see people doing this on their own instead of paying a body shop.

[Mr_Draco]

Originally Posted by caverman

I need help with figuring out what I’m doing wrong with painting my engine cover and how I can now fix it.

I taped off my engine cover and then wiped it down with a wet paper towel that had a couple drops of Dawn dish soap and then let it dry. I picked up a can of Rustoleum for Plastic at Home Depot.

The first time I sprayed it came out almost perfect. There were a couple minor specks/dirt in it. So my friend talked me into lightly sanding and re-spraying. I sanded a couple pieces out and let it sit overnight. In the morning I re-sprayed and it did this cracking you see in a couple spots. So, I sanded out most of the cracking and let is sit over night again. Spayed it the next afternoon when it was about 65 outside. I got some cracking again. Re-sanded....waited overnight....resprayed. This time it didn't crack. Waited several hours or so and sprayed some clear over it. On one side it immediately cracked. Other side is fine. I re-sand (can't get all the cracking out but got most of it)....re-spray....all is good. I let it sit overnight and then this morning I let it sit out in the sun for a good 3+ hrs. Bring it in let it cool down for about 30 mins. Re-spray the clear and it freakin starts immediately cracking. I'm done now....I've lost the battle. Have no idea what to do.

BTW: in between coats I've been wiping it down with the stuff I use to clean my granite. It's a mix of 70% water, 30% alcohol, and a couple drops of dish soap. I wouldn't think this would cause the problem but maybe it is???

Last year I bought a bunch of model cars and was painting them using Krylon Fusion spray paint then covering them with Krylon Clear. They always did this exact same thing. Come to find out it's as chef-beavis said.

Though my testing I found out that if you are going to paint over something that was just spray painted you must leave the item in a room where it is constantly at least 70 degrees for 1 week before painting. If you don't, the first coat will not completely cure and will do what you are experiencing.

[caverman]

Sanded it down and re-sprayed the red. So far...no cracking. It seemed to take a good coat. I'm going to let the sit probably 24 hrs or so and then give the clear a try.

Thanks for all the comments. I'll keep everyone posted.

[Iron Lung Jimmy]

Yes, chef-beavis got it right.

Read the back of the can, it will say something like "recoat within [some sort time period] or allow to dry [a much longer time period] before recoating". You have already exceeded the short time period so wait at least the longer time period before spraying it again.

I'd let it sit for a couple of days just to be sure.

[Taz_FL]

There’s nothing wrong with using dish detergent (in water) to clean your parts, you just don’t want to leave it on there. On my Dodge Dakota that I had I painted a bunch of the underhood plastic. What I did was took the parts I wanted to paint and cleaned them with hot water with dawn dish detergent in it. That removes oils very well. Then I rinsed with clean water, let everything dry and then wiped it down with rubbing alcohol. After that I sprayed a few coats of “adhesion promoter” for plastic, after that I sprayed some primer and then the paint. I did not sand the plastic prior to painting and my parts looked as good the day I got rid of the truck as they did the day I painted, we’re talking about 3 years.
Here’s some pics….

[Alfieboy]

Originally Posted by VChula

You can't use any type of primer on plastic. You'll need one with a flex additive. Auto-zone has primers with "adhesion promoters" specifically for use on plastics.

seen it first hand


A very good idea......

[caverman]

I kinda read the can a little wrong. It said dry to touch in 1 hr (at 70 degrees) and complete dry in 24hrs. So I figured I'll have to wait till tomorrow to spray a second coat. Then after I had spent some time talking with neighbors and cleaning up the garage after installing my Halltech CAI I ended up re-reading the can down further. I then see where is says to put a second coat within an hour or wait 48 hrs. Guess I'll have to wait a couple days to put another coat on.

What I don't know is how long to wait until I can apply the clear? Should I do it within the hour like a second coat or wait 48 hrs. My guess is that it's going to be 48 hrs.

[Mr_Draco]

Originally Posted by caverman

I kinda read the can a little wrong. It said dry to touch in 1 hr (at 70 degrees) and complete dry in 24hrs. So I figured I'll have to wait till tomorrow to spray a second coat. Then after I had spent some time talking with neighbors and cleaning up the garage after installing my Halltech CAI I ended up re-reading the can down further. I then see where is says to put a second coat within an hour or wait 48 hrs. Guess I'll have to wait a couple days to put another coat on.

What I don't know is how long to wait until I can apply the clear? Should I do it within the hour like a second coat or wait 48 hrs. My guess is that it's going to be 48 hrs.

For a clear coat you are better off waiting the longest recoat time. If you do it within an hour, the colors will kinda blend together and I'm pretty sure that is not what you're going for.

[Axtion]

I just used the same stuff and did my cover and am working on the Fuse Box now. I used Dish Soap and a sponge. Once done I rinsed real good and let dry. I did 3 coats within about 40 minutes and then let stand, without primer and or clearcoat. It does say within the first hour or wait a while. I think the someone else used clear coat with this paint and got the same effect you did.

[chevy 3]

Buy a can of prep spray and a can of bonding spay