Here's a pic showing where the cracks are (this is not my car, owner of this car please don't mind):



I tried to talk to the shop which painted it, but they just insist fiberglass cracks anyways...Is this the nature of fiberglass or the body shop just sucks?

Please help!

 

Well its not the bodyshop. Did you buy a knock off rear bumper?

 

It's a replica.

 

I have a small hairline crack in that area too and my rear bumper is an authentic kenstyle. I assuming that you're talking about the area where the corner of the rear bumper meets the car. The crack is half an inch long and so small you'd think it's a strand of hair on the bumper. The bodyshop probably applied too much pressure to that corner when installing the bumper.

 

I have the real deal. My car rolled out of my driveway and into a light pole a couple weeks ago. It SMASHED the passanger side of the bumper really good. Bumper was in two pieces. That area didnt crack at all. The real bumper has a nut serts molded into it. The fake one doesnt. So who knows if your body shop was able to attach the bumper right. Lack of support could cause the cracks.

 

Anything the body shop can do to prevent the cracking on that spot?

 

Yes add fiberglass to the inside.

 

This is a good example why most of us don't want
body kits made of fiberglass! The problem I've had
with fiberglass is in the painting....the primer and
paint must have a flexing agent added to them. If
not the paint starts to crack and if you get hit the
paint will litterally shatter.

 

But rear bumper rarely comes in polyurethane...

 

This is just the wrong info. Ive been doing autobody work for years now and have never had a problem. Its all about what you buy. If you buy a REAL kit you wont have probelms if its installed correct. I have a poly bumper on my Z and its a pain in the ****. The bumper sags in spots and I had to go through a lot more to prep it for paint. Until someone comes out with a ABS bumper like OEM Ill always buy glass.

 

if urethane were the best material, then why would the top aero part manufacturers in japan who sell products as dealer optional parts choose fiberglass?

do you have a pic of this that you can send me? i'd like to show it to kenstyle. that is very odd, unless you think it was caused by some kind of abnormal force or pressure.

 

Any fiberglass part can crack,if impacted in the right spot.Even my authentic Kenstyle bumpers have been subjected to enough impact to crack.I am really amazed though how well they stood up to the impacts with just minor damage.Both have been repaired sucessfully without any indication of damage.

 

[quote=BPAUTO]if urethane were the best material, then why would the top aero part manufacturers in japan who sell products as dealer optional parts choose fiberglass?

uhm Its a lot cheaper to produce Fiberglass or FRP, easier to work with and less environmental restrictions,

 

I always thought it was the other way around because the flexibility of polyurethane, you need the flexing agent in the paint so it can flex with the polyurethane. Guess I was wrong.