Repairing/Modifying the Bumper Fascia

information. I am in no way a professional and make no claims as such. I have used the methods I describe to good effect but I take no responsibility for any failure on your part in following these procedures. I am well aware that there are people who post to this board that are professionals at body repair and that any 'skills' that I possess are strictly of a DIY nature, learned from books and by doing and therefore subject to improvement and any input from the aforementioned professionals would be appreciated.

I not responsible for either damages to your car or to yourself if you follow these guidelines in an attempt to repair/modify your car. I have tried to note the precautions that need to be taken.

Every so often, someone will post up asking either how to repair or modify their stock bumper. In most instances, the answer is basically the same for either question. The 350Z’s bumper Fascia is made from TPO. That is Thermoplastic olefin.

Because of it’s properties it can prove difficult to repair/and or modify. It can be done though. It will simply require time to 'do it right' .. and if you are paying someone to do the repair then simply the labor cost involved will probably make it 'cheaper' to replace. If you are a DIY kinda guy/gal .. then read on.

TPO (a.k.a. TEO ~ Thermoplastic elastomer olefinic) is a blend of a polyolefin, usually polypropylene (PP) and an elastomer (usually a synthetic rubber, like EPDM). Because it is a polyolefin (or ‘oily’ plastic) many adhesives have a hard time with TPO. Because of the diversity of formulations in TPO, fusion welding procedures are difficult to perform because of incompatibility between the welding rod and base materials. Hot-melt adhesives work particularly well on TPOs due to their highly compatible formulation.

The process of repairing, refinishing, modification can be described with five steps: Identify, Clean, Align, Repair and Refinish.

(Fig 1) Fascia Markings

The bumper on the 350Z is made from TPO. The back of my bumper has the following inscribed in it- labeled >PP+EPM-T15< (Fig 1). The 'PP' stands for Polypropylene and the 'EPM' stands for an elastomer; a synthetic rubber. There are other labels identifying different plastics on other cars and on other parts of the Z but I am concentrating on the Z's bumper Fascia here, so I am only going to talk about TPO.

This is possibly the most important step in the process whatever the reason- repair or modification.

The bumper Fascia is exposed to many elements. On the outer surface you may have wax, dirt, tar, road salt, squished bugs and who knows what. Remains of various and assorted animals that failed to get out of the way in time. The inner surface may have mud, oil and transmission fluid splattered on it.

Therefore, in order for the repair materials/and or modification adhesives and primers to adhere to the plastic, it needs to first be cleaned.

Steps:

1) Clean with soap and water. If you have a fancy plastic cleaning prep soap, use that. If not, just use dish washing liquid. Using the prep soap is an advantage since they contain (usually) pumice/or fine grit blended in which will put a fine sand-scratch into the surface. This will aid in the adhesion of the first primer coat. It is also (for the same reason) a good idea to scrub the part with a scuff pad such as a 3M red Scotch-Brite pad. When finished, clean the part very thoroughly with clean water to remove the soap and grit. Let the part air dry thoroughly.

2) Some surface contaminants such as wax and grease will resist cleaning with just soap and water. For this second step, use a solvent-based plastic cleaning solution. Speaking in generalities, the procedure is basically the same- still read the instructions on the specific product you use. You work in a small area- six inch circle or so … spray on cleaner, let set for a few seconds and wipe off with a clean cloth.

Important: Wipe off the surface in one direction only. Wiping in a back and forth motion will simply recontaminate the surface. Again, wipe in one direction. Rotate the surface of the cloth so you are wiping using a clean surface of the cloth in one direction only. Continue doing this until the cloth is virtually unsoiled.

Congratulations. You have a clean surface.

When aligning the parts to be repaired be aware that TPO will not only tear after impact damage but also distort. TPO is a thermoplastic. Therefore you can use a heat gun to reshape the distorted area.

Using the high heat setting, heat only one side of the part. Move the gun around- don’t remain over one area too long or hold the gun too close to the surface. When the part becomes too uncomfortable to touch on the other side the plastic has been heated all the way through.

When the part is thoroughly heated use the handle of a screwdriver, a wooden block or your hands (wear gloves) to push the distortion back into place. You have to work quickly as the plastic cools rapidly. Once everything is aligned use a wet cloth to quickly quench it.

(Fig 2) Damage

(Fig 3) Gouge

Someone backed into me in a parking lot and gashed my front bumper (Fig 2 and Fig 3). From the damage .. they seem to have climbed up the bumper and onto the headlight, leaving a very deep gash in the bumper (and scratches on the headlight). I pushed the resulting deformation from the inside but still had a very 'nice' gash in the bumper. I didn't take a photo of the gouge before that but you could put your entire hand in it. Quite sad.

Note: I pushed the buckled in area back from the inside with my hand. If I had followed my own advice given earlier, I should have used a heat gun to soften the damaged area which would have allowed tear to be aligned better. Hey .. you learn. At the time I was just pissed ...

(Fig 4) Blue Tape

I outlined the area that needed repairing with blue painter's tape (Fig 4) in an attempt to keep any excess damage at a minimum. I was attempting to keep any sanding, welding and so on confined to the area to be repaired.

(Fig 5) Sanding

I used an orbital sander and a single edge razor blade to scrape away paint from the gouge. The use of the razor blade was simply because I had one. The portions of the gouge that were still below the 'surface' of the bumper could have been sanded by hand. In any case ... you are removing any paint so you have a working surface that is just plastic (Fig 5).

(Fig 6) Welding

I welded the gouge. People that do this for a living use a heat gun and a fusion welding rod. The problem there is that TPO comes in thousands of blends and finding a fusion welding rod that is close to the substrate you are repairing is difficult.

I simply melted the edges of the gouge, laid the strip of plastic down the gouge and then melted that into the substrate and used the single edge razor blade to blend it together.

I used my orbital sander then, to grind down the surface for the next step.

(Fig 9) Plastic Putty

The structural repair completed I used Evercoat's Poly-Flex Glazing Putty. This filler is made for”filling sand scratches, nicks, dings and gouges on flexible bumpers” (that's from the Poly-Flex sales flyer. It is flexible up to a 77° according to the flyer. In the flyer it mentions that”.. when repairing thermo plastics such as; TPO .. surfaces need to be oxidized by a flame treatment process prior to the application of Poly-Flex</I”. Ha. Done during my 'welding'.

(Fig 10) Mask

(Fig 11) More putty

(Fig 12) Primer

Normal finishing now. Sand. Prime. Sand. Prime. Until happy. Started with 320 grit wet/dry down to 1000 grit.

(Fig 13) Paint

Paint. I used spray paint in a can that I ordered from Automotive Touchup and it matches perfectly (at least for my CS). I have also found that some NAPA stores can mix paint that they will charge a spray can right there in the store. The paint is not IMO, as good a match as that from Automotive Touchup, but it is cheaper and I used it for the 'base coat' and used the more expensive Automotive Touchup for the final coat.

In any case, I masked off the hood, lights, emblem and grill. When I painted the repaired area I faded the new paint into the old and it blended very nicely. The photo of the finished repair is the paint after I finished. It still needs to sit for a while to let the paint dry. I figure two weeks. Then, it can be wet sanded and covered with a clear coat.

(Fig 14) Six Months

Six months later still looks 'good-nuf'. I still haven't wet sanded or clear coated ... Winter happened.