Hi Andy. Welcome to the madness lol.

Some of the bodywork guys will be able to advise you on that I'd say. Has the paint cracked along the repair lines?

Cooks

Sent from my D6603 using Tapatalk

 

Possibly too much paint applied too quickly.
As it dries the layers shrink at different rates and effectively pull the paint apart.

 

We don't know your process of repair. If you've just filled cracks in the plastic that simply won't make it strong enough, it needs to be reinforced from behind with a good 2 part plastic glue

 

Micro cracks opened up?

 

Thanks for the replies, I used fibreglass resin & matting on the back of the crack to give the strength back to the bumper, then flexible bumper filler. The bumper has not cracked again, but all of the newly painted area has gone as shown in the pictures, including the area when where I blended in to the existing paint. I think it is either the clear coat or the paint which has cracked, was hoping some one had seen this effect before!

 

is it a plastic bumper ?

if so fibre glass wasnt the right product for the back of it , and have you V'eed out the cracks before filling them

regardless sand it all off and start again...ideal with some pics when bare and you might get some advice

 

Too much paint and not allowing it to cure/dry enough between layers.

I had exactly this when I was painting some hard plastic RC body shells.

Only way to fix it is sand it right back and start again using much less and letting it dry properly.

 

Looks like paint too thick, and / or not enough drying time between layers. It looks like the paint itself has shrunk and cracked rather than the repair underneath failing.

 

Iam sorry to say mates, its the wrong idea blaming the paint.
If i understand correctly he sanded down he "repaired" the back with FG? And bondo the front ?


You cant slip with this you mist make a repair on both sides (in and out). Get you bumper sanded and tou can fiberglass it with a thin layer dont go mad! The thicker the harder and less flexibility there is, i wiuld however recommend a plastic repair or even weld the bumper with plastic rods. Anything else would get you in the same place you are now it wont hold the crack from one side only.

Yiu say its not cracked but pull it to the outside from in and. Watch its the same crack patterns.

Sent from my LG-H815 using Tapatalk

 

You can see the edges of the paint have sunk and rounded as its shrunk down.

Sure, the repair technique might not be ideal, but if it had been the repair underneath failing the cracks would have a sharp, hard edge to the where the filler had broken off the bumper, and would usually appear around the edge of the repair first.

 

Not when the backing repair is so hard and not flexible you see it moves but barely and paint is too thin to handle any movement at all.

Sent from my LG-H815 using Tapatalk

 

Trust me the effect in the photos was exactly the same as I had on the RC shells i mentioned in my post.

Its too much paint and not enough drying time simple as that.

 

I see this in my line of work all the time, it is called Alligatoring, it's caused by one of two things like has been mentioned, paint coat too thick or not allowing sufficient time for to cure between coats, pictures look more likely to point to paint applied to thick.

 

Once again thanks to all who have replied. If this does seem the most likely reason , my question would be how to avoid this happening again, just that I have read to leave no more that 20 mins between coats for the layers to bond chemically. I should mention that the primer was left for several days to dry

 

If that's the correct recommendations from the paint manufacturer then stick to the timing but thinner coats and should be fine.