I have a bumper i want to add drl lights to. The bumper doesn't conform perfectly to the lights. how should i go about contouring it to make it sit flush? i know i can't use putty cause i would need to build it too high and on such a flexible bumper it would def crack. how should i go about it? the bumper is ppu material. look forward to your advice. thanks
[url]http://i1322.photobucket.com/albums/u569/Sonatabadass/20150527_221035_zps6zjgoblf.jpg/[url]
[url]http://i1322.photobucket.com/albums/u569/Sonatabadass/20150527_220220_zpsgo53tqs3.jpg/[url]

Uhh, take a crack at those pictures again. Your links are not active.

Whoa.... that's a tall order there. I don't think molding anything into a Polypropylene like that is going to be practical for that size. It's more complicated but you'd be better off to take a mold off the whole bumper (can be done with even simple plaster), cast that in fiberglass, then you could easily glass in the lights. Trying to get anything to "stick" to that poly is going to require more poly material to be "welded"into it. Not saying it can't be done but molding is a lot easier.

DarrelK wrote:Whoa.... that's a tall order there. I don't think molding anything into a Polypropylene like that is going to be practical for that size. It's more complicated but you'd be better off to take a mold off the whole bumper (can be done with even simple plaster), cast that in fiberglass, then you could easily glass in the lights. Trying to get anything to "stick" to that poly is going to require more poly material to be "welded"into it. Not saying it can't be done but molding is a lot easier.

Thanks for the response. So your saying just remake the entire bumper out of fiberglass then I can build those areas with fiberglass. Wouldn't the welding be a lot cheaper? Someone suggested 3m plastic adhesive would that even work? Would that stick and then be sanded down?

The only reason I bring up remolding the entire bumper is most people are kind of "scared" of plastic welding. Combine that with the fact that "el cheapo" welders don't work very good and you've got a recipe for a messed up original bumper. Doing a mold lets you keep your original bumper but gives you a quality new bumper made of one strong, durable material. Most of the adhesives show great promise "up front" but usually start failing when the materials go through a few heat and cold cycles. It's that same old story.... different materials, different rates of expansion/contraction.

DarrelK wrote:The only reason I bring up remolding the entire bumper is most people are kind of "scared" of plastic welding. Combine that with the fact that "el cheapo" welders don't work very good and you've got a recipe for a messed up original bumper. Doing a mold lets you keep your original bumper but gives you a quality new bumper made of one strong, durable material. Most of the adhesives show great promise "up front" but usually start failing when the materials go through a few heat and cold cycles. It's that same old story.... different materials, different rates of expansion/contraction.

Gotcha. If I make the mold out of plaster how would I go about that? Could I cover the bumper with plastic or aluminum foil and lay the fiberglass directly over it instead of making a mold?

Easiest thing to do is look up "moldmaking" on YouTube. You'll see a lot of different ways that they are done. You could do what your are talking about there with laying the fiberglass directly over a "barrier" which would be on the bumper but the downside is it will be a somewhat "dirty" replica of the bumper. If you kept that outer layup "thin" it would be more accurate and you could always add more resin/mat from the inside to give it body and strength. I have seen this done a few times, but it does require a lot of time spent "shaping" to get a more accurate surface. Molded surfaces require very little surfacing.

DarrelK wrote:Easiest thing to do is look up "moldmaking" on YouTube. You'll see a lot of different ways that they are done. You could do what your are talking about there with laying the fiberglass directly over a "barrier" which would be on the bumper but the downside is it will be a somewhat "dirty" replica of the bumper. If you kept that outer layup "thin" it would be more accurate and you could always add more resin/mat from the inside to give it body and strength. I have seen this done a few times, but it does require a lot of time spent "shaping" to get a more accurate surface. Molded surfaces require very little surfacing.

Ok I'm all about doing things properly so how would you go about it? After you initially told me about the plaster approach I looked up a couple videos but I was just confused about doing it on a larger scale. Could you refer me to a specific video? If I know the right steps to take I can get it done

There used to be one specific video with a guy using both plaster of paris and just plain old drywall mud for casting on Youtube but it looks like it isn't on there anymore. It's been about 7 years back or so that 80-Grit Guy on this forum was describing how he used drywall mud to make his larger molds. Try and look up posts by him on here. I do mostly fiberglass molding of parts and don't get into these large molds too often. Most of my stuff is "lost foam" casting of original parts that I make, entirely different than what you need to do to replicate a bumper cover.