Thermoplastic Bumper Cover, 1997 Bounder

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Shuttersparks

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Jul 4, 2018
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Can anyone identify the type of thermoplastic used in the 1997 Bounder front bumper cover and end caps?

There was a brush fire near the front of the coach and the thermal radiation softened and distorted some of the plastics.

There's a heavy textured coating to make the bumpers look more substantial. Underneath is a shiny hard yellowish plastic that is easily softened and reshaped. My first guess was ABS but I tried a solvent plumbing cement for ABS and it seemed to have no effect. (This was a cursory test). That made me think it might be a urethane.

Rather than fool around with experiments, I thought to ask here in case someone knows the right answer.

I need to know so I know what kind of adhesives and fillers will bond to this stuff.

Thank you in advance!
 

Frank B

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Apr 23, 2005
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Calgary, Alberta
Is this on a Dodge chassis? If so, forget about trying to fix it.


You can sometimes use a heat gun and a blunt instrument like the back of a screwdriver handle to push out some distortion from the back side of the bumper. After that, standard flexible body filler will do the job. Just rough up the surface really well and blow it clean before you apply the filler.  However, if the distortion is severe, it won't be very pretty.

I ran a small Auto touch up business for many years, and found that Dodge used what appeared to be a polypropylene foam in their bumper covers. ABS can be melted together with a soldering gun. Polypropylene foam just evaporates. We never found anything that would really fix it. ABS is black, but what I think is a polypropylene foam was yellow. However, I cannot say for certain what that plastic really is.


Do you have comprehensive insurance on your Bounder? If so, your Insurance may cover that. Often, there is zero deductible on comprehensive. If the original parts are no longer available, then perhaps an aftermarket aluminum bumper?  Failing that, then perhaps you are looking at an RV wrecking yard of some description.
 

Shuttersparks

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Hi Frank,

Thank you very much for the reply. The chassis is Chevy 454 gas. The bumper parts were rotomolded, almost surely from ABS. It's solid, not foam and no fibers or fillers that I can detect. Replacement fiberglass ones cost $5,600 just for the center section and I need to end caps too, so double that. Hah. Fleetwood has no records from before 2009 so they have no idea what they've made of.

I'm not messing with insurance because they would total it and I don't want that. I have way to much time and money invested in customization and improvements to the coach.

I've been stripping the outer textured coating. After that comes the heat gun to reshape what I can and reduce the amount of filler needed.

I have a segment I can experiment on. I plan to try something I've never done before, which is to make filler from dissolved ABS. I have five pounds of ABS pellets coming. I plan to dissolve them in acetone over a couple of days to make a paste that I can spread onto areas that have been stripped and hit with adpro. It ought to make a solid bond.  If not, I'll try something else.

Thank you again,
Phil
 

Frank B

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Apr 23, 2005
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Calgary, Alberta
Phil:


If you are going to try to reshape the bumper, something that will allow you to work on a wider area at a time is a heat lamp.  The largest one can get on a typical house circuit is a 1500 watt unit like this:


https://www.ebay.com/itm/Infratech-14-1000-Portable-Infrared-Curing-Lamp-1500-Watt-/142267080872


Do be aware that a heat lamp like the one I linked is capable of melting the bumper skin even worse if left on unattended.  I've done it.  :-(


It can be placed a couple of feet away from the bumper until the plastic skin gets pliable all the way through, then use whatever blunt device you wish on either the front or the back side of the bumper skin to 'massage' the bumper skin back into shape.  If it won't 'hold' where you want it, try pushing it to where it should be and hold it there while you spray it with water to cool it off.  This will cause it to 'set' in that shape.  (At least until the next time it gets really hot.)  We used a 1 litre plastic bottle of tap water with a hand pump adjusted to provide a fine spray.


As to your idea of solvent and ABS plastic beads to create a paste, I've never tried that.  I do know, however, that solvent can cause plastic to swell.  When it dries, it will shrink, and may crack.


Flexible body filler (Bondo) is made for this purpose, and even it will shrink to some degree.  FLEXIBLE lightweight filler works best. Put it on in layers, and let it set a day or so after each layer is applied.  Sand a bit between applications so you don't cover over air bubbles.  Blow the surface clean with an air jet before applying the next layer. Body filler needs a relatively smooth surface to bond to.  Don't try to fill a deep depression all in one big gob.  It will eventually crack or split when it shrinks.



You can use some fiberglass mesh drywall tape to strengthen thicker areas in the same way it is made to be used with drywall.  Just 'paste' it into the repair.  Cover it over again with another thin skim of flexible filler once you have sanded down to the shape you want.  You don't want fiberglass 'hairs' from the drywall tape sticking out of the surface, as it may 'wick' up into the primer and ruin the base for the paint.


100 grit dry paper on a random orbital hand sander will make short work of shaping the filler.  It is too coarse for the final finishing before primer (220 for that), but it is fast and does not fill quickly like a finer paper.  Finish the primer with 400 grit wet paper, or even 600 grit if the paint will be metallic.  Metallic paint shows underlying scratches more than a monochrome paint.


Have fun!  Do let us know how it works out for you.  And, there is still the possibility of finding a used part in a wrecking yard, and saving you a lot of time.


Frank.
 

72cougarxr7

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Location
Watertown NY
Is the bumper flexible or rigid plastic.
ABS tends to be more rigid and urethane bumpers tend to be more soft and flexible.

I would be weary of trying to make a plastic patch, remember the acetone you are trying to dissolve the plastic pellets into will also start dissolving the bumper when you apply it.
I work in parts at a body shop, 3M makes a few different products designed to repair plastic bumpers.
Many of them are 2 part products that come in a "double barrel" caulk tube and mix in a special nozzle when dispensed.
They also have instructions on their website on how to properly do the repairs.
https://www.3m.com/3M/en_US/collision-repair-us/applications/bumper-and-plastic-repair/

Standard plastic body filler (Bondo, etc) can be used on most plastic bumpers , but must be kept thin or you will risk having it crack or separate.
So get the plastic as close to the proper shape you can.

An electric heat gun should be all you need. Available  at Harbor freight for around $20, they are like a blow dryer on steroids, and get quite hot.
Get it hot, work from the back side with a body dolly or screw driver handle.
You may have to cool it with a wet rag while holding the shape from the backside.
May take several cycles of this to get the shape you need.

Don't be tempted to take a propane torch to it! This will get the plastic to hot and can damage it. Overheat the plastic and it may become brittle and crack.
Even the heat gun can overheat the plastic eventually, but much harder to do.

Good luck with your repair!
Post some pics if you can so we can see what you are working with.

 

Shuttersparks

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Jul 4, 2018
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Wow, thanks for all the tips. I'll put them all to use.

Good point about the swelling ABS and subsequent shrinkage. I hadn't thought about that. Maybe making my own isn't such a hot idea.

Good point about preheating. I happen to have two 1500 watt quartz radiant heaters that would do the job. They work really well for defrosting frozen pipes.

The plastic is hard and tough, averaging 0.2 to 0.25 inches thick.

I'll post photos. Picture is worth a thousand words.

I should mention that my goal is not to restore the exact original shape, but create something that looks good and doesn't fall apart. So, unlike a body shop, I'm free to do whatever. This is a good learning experience.

I also plan to experiment with plastic welding using the ABS pellets.

I had read that ordinary Bondo isn't great for my problem, but Bondo Putty is. So, I have a quart of that coming to see how well it sticks.

I'll post photos etc when time permits.

Thank you, again.
 
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