painting plastic grill, paint cracking and peels

[pow3rslave]

pulled my car off the road for a bit to respray the parts that were looking average. the lower lip had bits cracking off it so i sanded those bits back, cleaned it with k+h wax and grease remover then sprayed k+h plastic prime down before painting, it's come up sweet, just needs more red and a clear coat

also started work on the letterbox grill. cos after ages of neglect it had weird, long cracks appear in the top coat of paint, with the original red showing through them. here's what i did.

1) sanded it back in some bits right through to the plastic, others just leveled out the cracked bits.
2) cleaned it with the K+h wax and grease stuff, wiped it off afterwards
3) put down a couple of coats of K+h grey plastic primer

after this the primer dried and some bits of it had a lizzard scale look of cracks, so i sanded those bits and redid them.

came back later and tried to sand same bits, only to find that if i put my thumb on them with pressure and rub slightly, it all comes off, like primer and the red under it. leaving sticky bit.

what do you guys reckon? is this from the wax and grease remover? have i ****ed something up. will these sticky areas dry eventually so i can start over?

 

[Ozzie]

First of all this is the wrong section. ( you should know that by now)

but it sounds like the surface either wasnt cleaned properly, sanded properly or if there was moisture in the air it can do it too.

You need to prep it properly if you want it to turn out mint

 

[kart_racer]

Did you add flexi-add to the paint? If you don't do this the paint will crack as soon as the plastic flexes.

 

[pow3rslave]

nah it's a solid plastic grille, so there's no flex to it. or reason for it to bend at all

 

[Calaber]

The grille isn't a very big component. Your paint may be reacting with the old paint, so it would be worthwhile removing all of it and starting with a nice clean panel.

1. Wet rub all paint off - take it back to bare plastic all over. Don't use coarse wet and dry.
2. Wash down with wax and grease remover to remove all fingerprints/body oil from handling. Wear latex gloves if you need to when handling the grille after rubbing it back.
3. Prime with plastic primer to ensure adhesion with the undercoat
4. Spray two or three undercoats and let dry thoroughly
5. Wet rub undercoat and let dry (1200)
6. Spray top coats (2 to 3 coats, wet rubbing between coats but not final coat(1200 - 1500)
7. Spray with two or three coats of clear.
8. Polish with light abrasive polish when paint has fully cured. (Give it a week or so)

 

[Zeussy]

^^^^ Agreed IMO,

itl most likely be the new paint reacting with the old paint, mixing enamel with acrylic, or vice versa..
causing crows feet...