Greetings to all! I have rejoined the world of the living, chemo keeps getting in the way of my hobbies. Thanks again to 7TRoadster for asking where I was!
Speaking of 7TRoadster, I have been following his excellent guide for refinishing with one exception which I shall explain. The car had original paint, and upon stripping I observed that first was the finish, then a light grey primer that was probably some kind of polyester based primer, then a hard, black primer that I believe was an epoxy based primer, and finally the bare SMC panels. The black primer was noticeably harder than the SMC.
So, the deviation is that I intend to spray the bare SMC with Southern Polyurethane black epoxy primer. I called the nice folks at SPI and they informed me that the epoxy primer was 100% compatible with SMC and it would make the perfect surface for the FeatherFill. In addition, they tell me that it also is an excellent choice for the urethane bumper covers and did not require any flex additive or adhesion promoter.
The main reason I'm doing this is that there is the possibility of unforseen interruptions due to health concerns. I want to get that naked SMC sealed up and durable in case I have another delay. Naked SMC will soak up just about anything that touches it, sometimes irreparably. So that's the deal.
Speaking of bumper covers, that brings me to the next topic in this build thread. The bumper covers are original. The rear is flawless but the front has an impact hole in the lower passenger side. The bumper covers are the yellow PUR stuff common to early 80's GM vehicles. Since there is no damage other than the hole/tear, I believe it's a good candidate for repair. I have refinished several bumper covers in my day, but this is my first foray into actual repair. I'll document it in real time as much as possible, so if I screw something up you'll get to see it first hand!
First, here's the products I'll be using. As always, READ AND HEED THE SAFETY WARNINGS AND PRECAUTIONS!
Here's some pics of the damage on the outside of the cover. To complicate the repair, at some point in the past someone had attempted an amateur repair using what I believe to be super glue, lacquer based spot putty, and rattle can paint. It was a mess. Anyway, in these pics I have prepped the crack lines, drilled relief holes, and smoothed out the crack surfaces so that there are no sharp edges anywhere.
Now for the inside repair on the cover. According to 3M, you want the inside to be absolutely clean and smooth. Any overspray should be removed so that the patch is applied only to clean, bare urethane. Again, no sharp edges.
To temporarily hold the cracked segments of the bumper cover in place I used foil tape on the outside of the cover. For this picture, I haven't applied the third piece of tape so that you can see the prepared cracks and relief holes.
Now we get to the part where I applied the 3M 05888 bumper patch kit. Using paper for a template, I cut out a patch that would cover the entire cracked area in one piece. That turned out to be a mistake. I'll tell you why in a minute. By the way, 3M says that if your repair area is bigger than the patch then you should probably consider replacement rather than repair.
Here's where I got into trouble. I was a little too confident that I could push the patch down into a confined area with several compound curves. My plan was to heat the patch with a heat gun to make it more flexible.
But here's the deal. The patch kit comes with a packet of adhesion promoter. It's a small sponge impregnated with the promoter. You wipe it on the bumper cover and wait 5 minutes. Then you peel the backing off of the patch material. I'm here to tell you this is the most aggressive adhesive I've ever seen. It's almost like a magnet pulling the patch toward the cover. When the patch touches the cover it instantly becomes one with the cover and the universe! You WILL NOT be able to reposition the patch AT ALL! So, I wound up missing one small area where a crack needed to be bonded. After consulting with 3M, they recommended cutting another small patch that would cover up the exposed crack. They also said the patch material can be stacked, sort of a patch on a patch. What you don't want is a crack that follows along the edge of the patch. In retrospect, careful placement of multiple patches would probably have been better, but as it is all the cracks are bonded under the patches so I think I'm good to go.
Finally, on the outside, I bonded the cracks with 3M 05887 flexible bumper repair adhesive. I used 3M 05907 adhesion promoter on the bare urethane anywhere the adhesive would go. The 05887 is a 2 part mix, and has a very fast cure time. Accordingly, I used one of the 3M mixing nozzles so that I wouldn't have to screw around mixing while the stuff cures. This is good for repair shops because it can be sanded after about 15 minutes. But the working time is only around 3 minutes, so have all your materials at hand and have a plan for what you are going to do, and don't go to sleep while working with it. Squirt enough out to thoroughly bond the cracks/damage with a little extra for smoothing with a squeegee, like Bondo. But it will not squeegee into a smooth feather edge like Bondo or Dolphin Skin. At least not for me. And when it starts to set up, STOP IMMEDIATELY! Don't try to force it around, it will only get worse. Just walk away for 20 min or so.
After it's cured, you will be surprised how it sands if you've never used it before. Even though the stuff is very flexible, and the sanding effort is almost identical to the urethane material, it will not clog your sandpaper at all. Even though I've always been a wet sanding fan, this stuff seems to work better dry. In the pics below you can see what it looks like cured but unsanded, then what it looks like with a quick few minutes from the sanding block. Still have a few low places that need more material but all in all I think it will be a success.
Next up: I plan to spray the black epoxy primer in the morning unless the humidity is wacko. I'll be using my newly built fresh, filtered air supply system that emulates a downdraft spray booth. I'm confident it's going to work quite well but if it doesn't, you will find out about it right here!!
And it's great to be back!!