plastic to plastic fiberglass????????

[parkinglottc]

hello, i have a 1993 honda civic, and i bought a rear lip to go on the back bumper and i have some questions!! i have read that the bondo will crack unless its just lightly applied to cover fiberglass or metal. i would like to fill in the seam that this lip leaves on the bumper. can you use fiberglass on plastic or urethane? i have a friend that says you cant but i dont see any other way!! i dont want to bondo it. unless its to just cover the fiberglass, what fiberglass would i use if its possible? also what would be the best wat to attach it with the screws that were given? thanks!!!

[lkailburn]

yep you can use fiberglass to mold/blend. i know from personal experience that fiberglass will stick to your bumper lol...don't ask about it haha

and yes you are correct in saying that large amounts of bondo will crack. so use as lil as possible. sand the fg smooth first before u use bondp

[eckoman_pdx]

Is the rear lip itself a urethane or fiberglass lip?

[Interlude]

Basically you want to mold the lip and the bumper together to get rid of the gap/seam right?

Most likely your bumper is ABS plastic, since most OEM bumpers are. If your lip is also ABS plastic, urethane or polyurethane then a good body shop will have no troubles molding them together using a flexible urethane filler. You cannot use "bondo" as it will definitely crack because of the flexibility the ABS plastic has.

If your lip is made out of fiberglass, then you are taking a big risk. Since you are miss-matching materials, there is a very high chance that it will crack regardless of what filler you use. The problem is that the bumper and the lip will have different levels of flexibility. If the bumper is stressed, (i.e. being installed on the car, getting hit, etc.) the bumper would flex slightly more than the fiberglass, and something is going to crack. If the fiberglass was made using a very flexible resin, then the chances of cracking will decrease, but will still be high.

So basically if your lip is plastic, go for it and use a urethane, flexible filler. If it is fiberglass, don't bother; you'll regret it.

[eckoman_pdx]

Originally Posted by Interlude

Basically you want to mold the lip and the bumper together to get rid of the gap/seam right?

Most likely your bumper is ABS plastic, since most OEM bumpers are. If your lip is also ABS plastic, urethane or polyurethane then a good body shop will have no troubles molding them together using a flexible urethane filler. You cannot use "bondo" as it will definitely crack because of the flexibility the ABS plastic has.

If your lip is made out of fiberglass, then you are taking a big risk. Since you are miss-matching materials, there is a very high chance that it will crack regardless of what filler you use. The problem is that the bumper and the lip will have different levels of flexibility. If the bumper is stressed, (i.e. being installed on the car, getting hit, etc.) the bumper would flex slightly more than the fiberglass, and something is going to crack. If the fiberglass was made using a very flexible resin, then the chances of cracking will decrease, but will still be high.

So basically of your lip is plastic, go for it and use a urethane, flexible filler. If it is fiberglass, don't bother; you'll regret it.

I asked the material for basicaly those very reasons. Trying to mold fiberglass to plastic or urethane will result in nasty cracks eventually among other things. Bondo always cracks. Crappiest product ever made.

[lkailburn]

i think if you used poly fg and cloth you could mold the fg to the bumper cover without any issues of cracking. especially if you use the right amount of resin. i've found it is very flexible. yes a bit less than a urethane bumper cover but still very flexible.

the more resin you use, the more stiff and brittle it will become. use just enough to saturate the cloth..key words are "just enough"

[integrawhat]

you can also use some expansion foam in any hollow non visible spaces under the area the two parts are joined to stiffen the lip and make the molded area less likely to flex and crack